diff --git a/.document b/.document
index ec2fa093261427..7c6d9967b1bbdf 100644
--- a/.document
+++ b/.document
@@ -23,6 +23,7 @@ nilclass.rb
 pack.rb
 ractor.rb
 string.rb
+symbol.rb
 timev.rb
 thread_sync.rb
 trace_point.rb
diff --git a/.github/workflows/mjit-bindgen.yml b/.github/workflows/mjit-bindgen.yml
index 1252d3b50987c6..7c1575634d8e74 100644
--- a/.github/workflows/mjit-bindgen.yml
+++ b/.github/workflows/mjit-bindgen.yml
@@ -28,8 +28,6 @@ jobs:
         include:
           - task: mjit-bindgen
       fail-fast: false
-    env:
-      SETARCH: ${{ matrix.arch && format('setarch {0}', matrix.arch) }}
     runs-on: ubuntu-20.04
     if: ${{ !contains(github.event.head_commit.message, '[DOC]') && !contains(github.event.pull_request.labels.*.name, 'Documentation') }}
     steps:
@@ -39,20 +37,20 @@ jobs:
         run: |
           echo "GNUMAKEFLAGS=-j$((1 + $(nproc --all)))" >> $GITHUB_ENV
       - name: Install libraries
-        env:
-          arch: ${{ matrix.arch }}
         run: |
           set -x
-          arch=${arch:+:${arch/i[3-6]86/i386}}
-          ${arch:+sudo dpkg --add-architecture ${arch#:}}
           sudo apt-get update -q || :
           sudo apt-get install --no-install-recommends -q -y \
-          ${arch:+cross}build-essential${arch/:/-} \
-          libssl-dev${arch} libyaml-dev${arch} libreadline6-dev${arch} \
-          zlib1g-dev${arch} libncurses5-dev${arch} libffi-dev${arch} \
-          libclang1-10${arch} \
-          bison autoconf ruby
-          sudo apt-get install -q -y pkg-config${arch} || :
+          build-essential \
+          libssl-dev libyaml-dev libreadline6-dev \
+          zlib1g-dev libncurses5-dev libffi-dev \
+          libclang1-10 \
+          bison autoconf
+          sudo apt-get install -q -y pkg-config || :
+      - name: Set up Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: '3.1'
       - name: git config
         run: |
           git config --global advice.detachedHead 0
@@ -72,15 +70,11 @@ jobs:
       - run: ./autogen.sh
         working-directory: src
       - name: Run configure
-        env:
-          arch: ${{ matrix.arch }}
-        run: >-
-          $SETARCH ../src/configure -C --disable-install-doc --prefix=$(pwd)/install --enable-yjit=dev_nodebug
-          ${arch:+--target=$arch-$OSTYPE --host=$arch-$OSTYPE}
-      - run: $SETARCH make incs
-      - run: $SETARCH make
-      - run: $SETARCH make install
-      - run: $SETARCH make ${{ matrix.task }}
+        run: ../src/configure -C --disable-install-doc --prefix=$(pwd)/install --enable-yjit=dev_nodebug
+      - run: make incs
+      - run: make
+      - run: make install
+      - run: make ${{ matrix.task }}
       - run: git diff --exit-code
         working-directory: src
       - uses: ruby/action-slack@v3.0.0
diff --git a/NEWS.md b/NEWS.md
index b4ecccc5c4e39b..bff9d1e7ab51b4 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -103,7 +103,8 @@ Note that each entry is kept to a minimum, see links for details.
 Note: We're only listing outstanding class updates.
 
 * Fiber::Scheduler
-    * Introduce `Fiber::Scheduler#io_select` for non-blocking `IO.select`. [[Feature #19060]]
+    * Introduce `Fiber::Scheduler#io_select` for non-blocking `IO.select`.
+    [[Feature #19060]]
 
 * IO
     * Introduce `IO#timeout=` and `IO#timeout` which can cause
@@ -115,6 +116,11 @@ Note: We're only listing outstanding class updates.
     STDIN.read # => Blocking operation timed out! (IO::TimeoutError)
     ```
 
+* UNIXSocket
+    * Add support for `UNIXSocket` on Windows. Emulate anonymous sockets. Add
+    support for `File.socket?` and `File::Stat#socket?` where possible.
+    [[Feature #19135]]
+
 * Class
     * `Class#attached_object`, which returns the object for which
       the receiver is the singleton class. Raises `TypeError` if the
@@ -239,7 +245,7 @@ Note: We're only listing outstanding class updates.
     * io-nonblock 0.1.1
     * io-wait 0.3.0.pre
     * ipaddr 1.2.4
-    * irb 1.4.2
+    * irb 1.4.3
     * json 2.6.2
     * logger 1.5.1
     * net-http 0.3.0
@@ -301,7 +307,22 @@ The following deprecated methods are removed.
 * `Psych` no longer bundles libyaml sources.
   And also `Fiddle` no longer bundles libffi sources.
   Users need to install the libyaml/libffi library themselves via the package
-  system. [[Feature #18571]]
+  manager like apt, yum, brew, etc.
+
+  Psych and fiddle supported the static build with specific version of libyaml
+  and libffi sources. You can build psych with libyaml-0.2.5 like this.
+
+  ```bash
+  $ ./configure --with-libyaml-source-dir=/path/to/libyaml-0.2.5
+  ```
+
+  And you can build fiddle with libffi-3.4.4 like this.
+
+  ```bash
+  $ ./configure --with-libffi-source-dir=/path/to/libffi-3.4.4
+  ```
+
+  [[Feature #18571]]
 
 ## C API updates
 
@@ -356,6 +377,7 @@ The following deprecated APIs are removed.
   doing it in a native thread called MJIT worker. [[Feature #18968]]
   * As a result, Microsoft Visual Studio (MSWIN) is no longer supported.
 * MinGW is no longer supported. [[Feature #18824]]
+* Rename `--mjit-min-calls` to `--mjit-call-threshold`.
 
 ## Static analysis
 
@@ -416,3 +438,4 @@ The following deprecated APIs are removed.
 [Feature #19026]: https://bugs.ruby-lang.org/issues/19026
 [Feature #19060]: https://bugs.ruby-lang.org/issues/19060
 [Bug #19100]:     https://bugs.ruby-lang.org/issues/19100
+[Feature #19135]: https://bugs.ruby-lang.org/issues/19135
diff --git a/README.md b/README.md
index 35ef2d9e8989bc..5b1f21abc90298 100644
--- a/README.md
+++ b/README.md
@@ -54,6 +54,50 @@ see [Building Ruby](doc/contributing/building_ruby.md)
 
 https://www.ruby-lang.org/
 
+## Commands
+
+The following commands are available on IRB.
+
+* `cwws`
+  * Show the current workspace.
+* `cb`, `cws`, `chws`
+  * Change the current workspace to an object.
+* `bindings`, `workspaces`
+  * Show workspaces.
+* `pushb`, `pushws`
+  * Push an object to the workspace stack.
+* `popb`, `popws`
+  * Pop a workspace from the workspace stack.
+* `load`
+  * Load a Ruby file.
+* `require`
+  * Require a Ruby file.
+* `source`
+  * Loads a given file in the current session.
+* `irb`
+  * Start a child IRB.
+* `jobs`
+  * List of current sessions.
+* `fg`
+  * Switches to the session of the given number.
+* `kill`
+  * Kills the session with the given number.
+* `help`
+  * Enter the mode to look up RI documents.
+* `irb_info`
+  * Show information about IRB.
+* `ls`
+  * Show methods, constants, and variables.
+    `-g [query]` or `-G [query]` allows you to filter out the output.
+* `measure`
+  * `measure` enables the mode to measure processing time. `measure :off` disables it.
+* `$`, `show_source`
+  * Show the source code of a given method or constant.
+* `@`, `whereami`
+  * Show the source code around binding.irb again.
+* `debug`
+  * Start the debugger of debug.gem.
+
 ## Documentation
 
 - [English](https://docs.ruby-lang.org/en/master/index.html)
diff --git a/array.c b/array.c
index 0b4998a47c0d1d..f242031b4fffb7 100644
--- a/array.c
+++ b/array.c
@@ -4555,7 +4555,7 @@ take_items(VALUE obj, long n)
     if (!NIL_P(result)) return rb_ary_subseq(result, 0, n);
     result = rb_ary_new2(n);
     args[0] = result; args[1] = (VALUE)n;
-    if (rb_check_block_call(obj, idEach, 0, 0, take_i, (VALUE)args) == Qundef)
+    if (UNDEF_P(rb_check_block_call(obj, idEach, 0, 0, take_i, (VALUE)args)))
         rb_raise(rb_eTypeError, "wrong argument type %"PRIsVALUE" (must respond to :each)",
                  rb_obj_class(obj));
     return result;
@@ -5048,7 +5048,7 @@ rb_ary_fill(int argc, VALUE *argv, VALUE ary)
         ARY_SET_LEN(ary, end);
     }
 
-    if (item == Qundef) {
+    if (UNDEF_P(item)) {
         VALUE v;
         long i;
 
@@ -5505,7 +5505,7 @@ rb_ary_cmp(VALUE ary1, VALUE ary2)
     if (NIL_P(ary2)) return Qnil;
     if (ary1 == ary2) return INT2FIX(0);
     v = rb_exec_recursive_paired(recursive_cmp, ary1, ary2, ary2);
-    if (v != Qundef) return v;
+    if (!UNDEF_P(v)) return v;
     len = RARRAY_LEN(ary1) - RARRAY_LEN(ary2);
     if (len == 0) return INT2FIX(0);
     if (len > 0) return INT2FIX(1);
@@ -6068,7 +6068,7 @@ rb_ary_max(int argc, VALUE *argv, VALUE ary)
     if (rb_block_given_p()) {
         for (i = 0; i < RARRAY_LEN(ary); i++) {
            v = RARRAY_AREF(ary, i);
-           if (result == Qundef || rb_cmpint(rb_yield_values(2, v, result), v, result) > 0) {
+           if (UNDEF_P(result) || rb_cmpint(rb_yield_values(2, v, result), v, result) > 0) {
                result = v;
            }
         }
@@ -6090,7 +6090,7 @@ rb_ary_max(int argc, VALUE *argv, VALUE ary)
             }
         }
     }
-    if (result == Qundef) return Qnil;
+    if (UNDEF_P(result)) return Qnil;
     return result;
 }
 
@@ -6237,7 +6237,7 @@ rb_ary_min(int argc, VALUE *argv, VALUE ary)
     if (rb_block_given_p()) {
         for (i = 0; i < RARRAY_LEN(ary); i++) {
            v = RARRAY_AREF(ary, i);
-           if (result == Qundef || rb_cmpint(rb_yield_values(2, v, result), v, result) < 0) {
+           if (UNDEF_P(result) || rb_cmpint(rb_yield_values(2, v, result), v, result) < 0) {
                result = v;
            }
         }
@@ -6259,7 +6259,7 @@ rb_ary_min(int argc, VALUE *argv, VALUE ary)
             }
         }
     }
-    if (result == Qundef) return Qnil;
+    if (UNDEF_P(result)) return Qnil;
     return result;
 }
 
@@ -8148,7 +8148,7 @@ finish_exact_sum(long n, VALUE r, VALUE v, int z)
 {
     if (n != 0)
         v = rb_fix_plus(LONG2FIX(n), v);
-    if (r != Qundef) {
+    if (!UNDEF_P(r)) {
         v = rb_rational_plus(r, v);
     }
     else if (!n && z) {
@@ -8227,7 +8227,7 @@ rb_ary_sum(int argc, VALUE *argv, VALUE ary)
         else if (RB_BIGNUM_TYPE_P(e))
             v = rb_big_plus(e, v);
         else if (RB_TYPE_P(e, T_RATIONAL)) {
-            if (r == Qundef)
+            if (UNDEF_P(r))
                 r = e;
             else
                 r = rb_rational_plus(r, e);
diff --git a/benchmark/lib/benchmark_driver/runner/mjit.rb b/benchmark/lib/benchmark_driver/runner/mjit.rb
index 1d4693e8be2a81..3a58a620dec5a4 100644
--- a/benchmark/lib/benchmark_driver/runner/mjit.rb
+++ b/benchmark/lib/benchmark_driver/runner/mjit.rb
@@ -16,7 +16,7 @@ def parse(**)
         job.prelude = "#{job.prelude}\n#{<<~EOS}"
           if defined?(RubyVM::MJIT) && RubyVM::MJIT.enabled?
             __bmdv_ruby_i = 0
-            while __bmdv_ruby_i < 10000 # jit_min_calls
+            while __bmdv_ruby_i < 10000 # MJIT call threshold
               #{job.script}
               __bmdv_ruby_i += 1
             end
diff --git a/bootstraptest/test_ractor.rb b/bootstraptest/test_ractor.rb
index 491c700a1c1c7c..16082ccd51f837 100644
--- a/bootstraptest/test_ractor.rb
+++ b/bootstraptest/test_ractor.rb
@@ -285,7 +285,7 @@ def test n
   30.times.map{|i|
     test i
   }
-} unless ENV['RUN_OPTS'] =~ /--jit-min-calls=5/ || # This always fails with --jit-wait --jit-min-calls=5
+} unless ENV['RUN_OPTS'] =~ /--mjit-call-threshold=5/ || # This always fails with --mjit-wait --mjit-call-threshold=5
   (ENV.key?('TRAVIS') && ENV['TRAVIS_CPU_ARCH'] == 'arm64') # https://bugs.ruby-lang.org/issues/17878
 
 # Exception for empty select
diff --git a/bootstraptest/test_yjit.rb b/bootstraptest/test_yjit.rb
index 46fb5838dc60f2..9bcead3065ac57 100644
--- a/bootstraptest/test_yjit.rb
+++ b/bootstraptest/test_yjit.rb
@@ -47,6 +47,29 @@ def call_graph_root
   Object.send(:remove_const, :Foo)
 }
 
+assert_normal_exit %q{
+  # Test to ensure send on overriden c functions
+  # doesn't corrupt the stack
+  class Bar
+    def bar(x)
+      x
+    end
+  end
+
+  class Foo
+    def bar
+      Bar.new
+    end
+  end
+
+  foo = Foo.new
+  # before this change, this line would error
+  # because "s" would still be on the stack
+  # String.to_s is the overridden method here
+  p foo.bar.bar("s".__send__(:to_s))
+}
+
+
 assert_equal '[nil, nil, nil, nil, nil, nil]', %q{
   [NilClass, TrueClass, FalseClass, Integer, Float, Symbol].each do |klass|
     klass.class_eval("def foo = @foo")
diff --git a/class.c b/class.c
index 85663ada50ab79..b9d62c18b19e83 100644
--- a/class.c
+++ b/class.c
@@ -64,7 +64,7 @@ push_subclass_entry_to_list(VALUE super, VALUE klass)
 void
 rb_class_subclass_add(VALUE super, VALUE klass)
 {
-    if (super && super != Qundef) {
+    if (super && !UNDEF_P(super)) {
         rb_subclass_entry_t *entry = push_subclass_entry_to_list(super, klass);
         RCLASS_SUBCLASS_ENTRY(klass) = entry;
     }
@@ -277,7 +277,7 @@ rb_class_update_superclasses(VALUE klass)
     VALUE super = RCLASS_SUPER(klass);
 
     if (!RB_TYPE_P(klass, T_CLASS)) return;
-    if (super == Qundef) return;
+    if (UNDEF_P(super)) return;
 
     // If the superclass array is already built
     if (RCLASS_SUPERCLASSES(klass))
@@ -608,7 +608,7 @@ rb_singleton_class_clone_and_attach(VALUE obj, VALUE attach)
             arg.klass = clone;
             rb_id_table_foreach(RCLASS_CONST_TBL(klass), clone_const_i, &arg);
         }
-        if (attach != Qundef) {
+        if (!UNDEF_P(attach)) {
             rb_singleton_class_attached(clone, attach);
         }
         RCLASS_M_TBL_INIT(clone);
diff --git a/common.mk b/common.mk
index ef4b952eda8937..24c1b39c4a2a34 100644
--- a/common.mk
+++ b/common.mk
@@ -249,19 +249,7 @@ mjit_config.h: Makefile
 
 .PHONY: mjit-bindgen
 mjit-bindgen:
-	$(Q)$(XRUBY) -C $(srcdir) -Ilib \
-		-e 'ENV["GEM_HOME"] = File.expand_path(".bundle")' \
-		-e 'ENV["BUNDLE_APP_CONFIG"] = File.expand_path(".bundle")' \
-		-e 'ENV["BUNDLE_PATH__SYSTEM"] = "true"' \
-		-e 'ENV["BUNDLE_WITHOUT"] = "lint doc"' \
-		-e 'load "spec/bundler/support/bundle.rb"' -- install --gemfile=tool/mjit/Gemfile
-	$(Q)$(XRUBY) -C $(srcdir) -Ilib \
-		-e 'ENV["GEM_HOME"] = File.expand_path(".bundle")' \
-		-e 'ENV["BUNDLE_APP_CONFIG"] = File.expand_path(".bundle")' \
-		-e 'ENV["BUNDLE_GEMFILE"] = "tool/mjit/Gemfile"' \
-		-e 'ENV["BUNDLE_PATH__SYSTEM"] = "true"' \
-		-e 'ENV["BUNDLE_WITHOUT"] = "lint doc"' \
-		-e 'load "spec/bundler/support/bundle.rb"' -- exec tool/mjit/bindgen.rb $(CURDIR)
+	$(Q) $(BASERUBY) -rrubygems -C $(srcdir)/tool/mjit bindgen.rb $(CURDIR)
 
 # These rules using MJIT_HEADER_SUFFIX must be in common.mk, not
 # Makefile.in, in order to override the macro in defs/universal.mk.
@@ -903,7 +891,7 @@ $(RBCONFIG): $(tooldir)/mkconfig.rb config.status $(srcdir)/version.h
 test-rubyspec: test-spec
 yes-test-rubyspec: yes-test-spec
 
-test-spec-precheck: programs
+test-spec-precheck: programs yes-fake
 
 test-spec: $(TEST_RUNNABLE)-test-spec
 yes-test-spec: test-spec-precheck
@@ -1104,6 +1092,7 @@ BUILTIN_RB_SRCS = \
 		$(srcdir)/array.rb \
 		$(srcdir)/kernel.rb \
 		$(srcdir)/ractor.rb \
+		$(srcdir)/symbol.rb \
 		$(srcdir)/timev.rb \
 		$(srcdir)/thread_sync.rb \
 		$(srcdir)/nilclass.rb \
@@ -6748,7 +6737,6 @@ gc.$(OBJEXT): {$(VPATH)}encoding.h
 gc.$(OBJEXT): {$(VPATH)}eval_intern.h
 gc.$(OBJEXT): {$(VPATH)}gc.c
 gc.$(OBJEXT): {$(VPATH)}gc.h
-gc.$(OBJEXT): {$(VPATH)}gc.rb
 gc.$(OBJEXT): {$(VPATH)}gc.rbinc
 gc.$(OBJEXT): {$(VPATH)}id.h
 gc.$(OBJEXT): {$(VPATH)}id_table.h
@@ -6967,7 +6955,6 @@ goruby.$(OBJEXT): {$(VPATH)}config.h
 goruby.$(OBJEXT): {$(VPATH)}constant.h
 goruby.$(OBJEXT): {$(VPATH)}defines.h
 goruby.$(OBJEXT): {$(VPATH)}golf_prelude.c
-goruby.$(OBJEXT): {$(VPATH)}golf_prelude.rb
 goruby.$(OBJEXT): {$(VPATH)}goruby.c
 goruby.$(OBJEXT): {$(VPATH)}id.h
 goruby.$(OBJEXT): {$(VPATH)}id_table.h
@@ -8354,7 +8341,6 @@ load.$(OBJEXT): {$(VPATH)}vm_core.h
 load.$(OBJEXT): {$(VPATH)}vm_opts.h
 loadpath.$(OBJEXT): $(hdrdir)/ruby/ruby.h
 loadpath.$(OBJEXT): $(hdrdir)/ruby/version.h
-loadpath.$(OBJEXT): $(top_srcdir)/revision.h
 loadpath.$(OBJEXT): $(top_srcdir)/version.h
 loadpath.$(OBJEXT): {$(VPATH)}assert.h
 loadpath.$(OBJEXT): {$(VPATH)}backward/2/assume.h
@@ -8510,6 +8496,7 @@ loadpath.$(OBJEXT): {$(VPATH)}internal/warning_push.h
 loadpath.$(OBJEXT): {$(VPATH)}internal/xmalloc.h
 loadpath.$(OBJEXT): {$(VPATH)}loadpath.c
 loadpath.$(OBJEXT): {$(VPATH)}missing.h
+loadpath.$(OBJEXT): {$(VPATH)}revision.h
 loadpath.$(OBJEXT): {$(VPATH)}st.h
 loadpath.$(OBJEXT): {$(VPATH)}subst.h
 loadpath.$(OBJEXT): {$(VPATH)}verconf.h
@@ -9600,6 +9587,7 @@ miniinit.$(OBJEXT): {$(VPATH)}ruby_atomic.h
 miniinit.$(OBJEXT): {$(VPATH)}shape.h
 miniinit.$(OBJEXT): {$(VPATH)}st.h
 miniinit.$(OBJEXT): {$(VPATH)}subst.h
+miniinit.$(OBJEXT): {$(VPATH)}symbol.rb
 miniinit.$(OBJEXT): {$(VPATH)}thread_$(THREAD_MODEL).h
 miniinit.$(OBJEXT): {$(VPATH)}thread_native.h
 miniinit.$(OBJEXT): {$(VPATH)}thread_sync.rb
@@ -9813,7 +9801,6 @@ mjit.$(OBJEXT): {$(VPATH)}method.h
 mjit.$(OBJEXT): {$(VPATH)}missing.h
 mjit.$(OBJEXT): {$(VPATH)}mjit.c
 mjit.$(OBJEXT): {$(VPATH)}mjit.h
-mjit.$(OBJEXT): {$(VPATH)}mjit.rb
 mjit.$(OBJEXT): {$(VPATH)}mjit.rbinc
 mjit.$(OBJEXT): {$(VPATH)}mjit_config.h
 mjit.$(OBJEXT): {$(VPATH)}mjit_unit.h
@@ -10029,7 +10016,6 @@ mjit_compiler.$(OBJEXT): {$(VPATH)}mjit_c.rbinc
 mjit_compiler.$(OBJEXT): {$(VPATH)}mjit_compile_attr.inc
 mjit_compiler.$(OBJEXT): {$(VPATH)}mjit_compiler.c
 mjit_compiler.$(OBJEXT): {$(VPATH)}mjit_compiler.h
-mjit_compiler.$(OBJEXT): {$(VPATH)}mjit_compiler.rb
 mjit_compiler.$(OBJEXT): {$(VPATH)}mjit_compiler.rbinc
 mjit_compiler.$(OBJEXT): {$(VPATH)}mjit_unit.h
 mjit_compiler.$(OBJEXT): {$(VPATH)}node.h
@@ -10423,7 +10409,6 @@ numeric.$(OBJEXT): {$(VPATH)}internal/warning_push.h
 numeric.$(OBJEXT): {$(VPATH)}internal/xmalloc.h
 numeric.$(OBJEXT): {$(VPATH)}missing.h
 numeric.$(OBJEXT): {$(VPATH)}numeric.c
-numeric.$(OBJEXT): {$(VPATH)}numeric.rb
 numeric.$(OBJEXT): {$(VPATH)}numeric.rbinc
 numeric.$(OBJEXT): {$(VPATH)}onigmo.h
 numeric.$(OBJEXT): {$(VPATH)}oniguruma.h
@@ -10621,7 +10606,6 @@ object.$(OBJEXT): {$(VPATH)}internal/value_type.h
 object.$(OBJEXT): {$(VPATH)}internal/variable.h
 object.$(OBJEXT): {$(VPATH)}internal/warning_push.h
 object.$(OBJEXT): {$(VPATH)}internal/xmalloc.h
-object.$(OBJEXT): {$(VPATH)}kernel.rb
 object.$(OBJEXT): {$(VPATH)}kernel.rbinc
 object.$(OBJEXT): {$(VPATH)}missing.h
 object.$(OBJEXT): {$(VPATH)}nilclass.rbinc
@@ -11666,7 +11650,6 @@ ractor.$(OBJEXT): {$(VPATH)}onigmo.h
 ractor.$(OBJEXT): {$(VPATH)}oniguruma.h
 ractor.$(OBJEXT): {$(VPATH)}ractor.c
 ractor.$(OBJEXT): {$(VPATH)}ractor.h
-ractor.$(OBJEXT): {$(VPATH)}ractor.rb
 ractor.$(OBJEXT): {$(VPATH)}ractor.rbinc
 ractor.$(OBJEXT): {$(VPATH)}ractor_core.h
 ractor.$(OBJEXT): {$(VPATH)}ruby_assert.h
@@ -15425,6 +15408,7 @@ symbol.$(OBJEXT): {$(VPATH)}backward/2/limits.h
 symbol.$(OBJEXT): {$(VPATH)}backward/2/long_long.h
 symbol.$(OBJEXT): {$(VPATH)}backward/2/stdalign.h
 symbol.$(OBJEXT): {$(VPATH)}backward/2/stdarg.h
+symbol.$(OBJEXT): {$(VPATH)}builtin.h
 symbol.$(OBJEXT): {$(VPATH)}config.h
 symbol.$(OBJEXT): {$(VPATH)}constant.h
 symbol.$(OBJEXT): {$(VPATH)}debug_counter.h
@@ -15597,6 +15581,8 @@ symbol.$(OBJEXT): {$(VPATH)}st.h
 symbol.$(OBJEXT): {$(VPATH)}subst.h
 symbol.$(OBJEXT): {$(VPATH)}symbol.c
 symbol.$(OBJEXT): {$(VPATH)}symbol.h
+symbol.$(OBJEXT): {$(VPATH)}symbol.rb
+symbol.$(OBJEXT): {$(VPATH)}symbol.rbinc
 symbol.$(OBJEXT): {$(VPATH)}vm_debug.h
 symbol.$(OBJEXT): {$(VPATH)}vm_sync.h
 thread.$(OBJEXT): $(CCAN_DIR)/check_type/check_type.h
@@ -15822,7 +15808,6 @@ thread.$(OBJEXT): {$(VPATH)}thread_$(THREAD_MODEL).c
 thread.$(OBJEXT): {$(VPATH)}thread_$(THREAD_MODEL).h
 thread.$(OBJEXT): {$(VPATH)}thread_native.h
 thread.$(OBJEXT): {$(VPATH)}thread_sync.c
-thread.$(OBJEXT): {$(VPATH)}thread_sync.rb
 thread.$(OBJEXT): {$(VPATH)}thread_sync.rbinc
 thread.$(OBJEXT): {$(VPATH)}timev.h
 thread.$(OBJEXT): {$(VPATH)}vm_core.h
@@ -16788,7 +16773,6 @@ version.$(OBJEXT): $(top_srcdir)/internal/static_assert.h
 version.$(OBJEXT): $(top_srcdir)/internal/variable.h
 version.$(OBJEXT): $(top_srcdir)/internal/vm.h
 version.$(OBJEXT): $(top_srcdir)/internal/warnings.h
-version.$(OBJEXT): $(top_srcdir)/revision.h
 version.$(OBJEXT): $(top_srcdir)/version.h
 version.$(OBJEXT): {$(VPATH)}assert.h
 version.$(OBJEXT): {$(VPATH)}atomic.h
@@ -16953,6 +16937,7 @@ version.$(OBJEXT): {$(VPATH)}method.h
 version.$(OBJEXT): {$(VPATH)}missing.h
 version.$(OBJEXT): {$(VPATH)}mjit.h
 version.$(OBJEXT): {$(VPATH)}node.h
+version.$(OBJEXT): {$(VPATH)}revision.h
 version.$(OBJEXT): {$(VPATH)}ruby_assert.h
 version.$(OBJEXT): {$(VPATH)}ruby_atomic.h
 version.$(OBJEXT): {$(VPATH)}shape.h
@@ -18229,6 +18214,5 @@ yjit.$(OBJEXT): {$(VPATH)}vm_opts.h
 yjit.$(OBJEXT): {$(VPATH)}vm_sync.h
 yjit.$(OBJEXT): {$(VPATH)}yjit.c
 yjit.$(OBJEXT): {$(VPATH)}yjit.h
-yjit.$(OBJEXT): {$(VPATH)}yjit.rb
 yjit.$(OBJEXT): {$(VPATH)}yjit.rbinc
 # AUTOGENERATED DEPENDENCIES END
diff --git a/compar.c b/compar.c
index 00e79b5767dc4c..3635d23e79561f 100644
--- a/compar.c
+++ b/compar.c
@@ -50,7 +50,7 @@ VALUE
 rb_invcmp(VALUE x, VALUE y)
 {
     VALUE invcmp = rb_exec_recursive(invcmp_recursive, x, y);
-    if (invcmp == Qundef || NIL_P(invcmp)) {
+    if (UNDEF_P(invcmp) || NIL_P(invcmp)) {
         return Qnil;
     }
     else {
diff --git a/compile.c b/compile.c
index d8d2738eb8919b..c047408b151042 100644
--- a/compile.c
+++ b/compile.c
@@ -4820,7 +4820,7 @@ when_vals(rb_iseq_t *iseq, LINK_ANCHOR *const cond_seq, const NODE *vals,
         const NODE *val = vals->nd_head;
         VALUE lit = rb_node_case_when_optimizable_literal(val);
 
-        if (lit == Qundef) {
+        if (UNDEF_P(lit)) {
             only_special_literals = 0;
         }
         else if (NIL_P(rb_hash_lookup(literals, lit))) {
@@ -7394,7 +7394,7 @@ compile_loop(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const node, in
     ADD_LABEL(ret, end_label);
     ADD_ADJUST_RESTORE(ret, adjust_label);
 
-    if (node->nd_state == Qundef) {
+    if (UNDEF_P(node->nd_state)) {
         /* ADD_INSN(ret, line_node, putundef); */
         COMPILE_ERROR(ERROR_ARGS "unsupported: putundef");
         return COMPILE_NG;
diff --git a/complex.c b/complex.c
index d927f62d5578ec..e9981863c21cb3 100644
--- a/complex.c
+++ b/complex.c
@@ -561,7 +561,7 @@ nucomp_f_complex(int argc, VALUE *argv, VALUE klass)
     if (!NIL_P(opts)) {
         raise = rb_opts_exception_p(opts, raise);
     }
-    if (argc > 0 && CLASS_OF(a1) == rb_cComplex && a2 == Qundef) {
+    if (argc > 0 && CLASS_OF(a1) == rb_cComplex && UNDEF_P(a2)) {
         return a1;
     }
     return nucomp_convert(rb_cComplex, a1, a2, raise);
@@ -2107,11 +2107,11 @@ nucomp_convert(VALUE klass, VALUE a1, VALUE a2, int raise)
     }
 
     if (RB_TYPE_P(a1, T_COMPLEX)) {
-        if (a2 == Qundef || (k_exact_zero_p(a2)))
+        if (UNDEF_P(a2) || (k_exact_zero_p(a2)))
             return a1;
     }
 
-    if (a2 == Qundef) {
+    if (UNDEF_P(a2)) {
         if (k_numeric_p(a1) && !f_real_p(a1))
             return a1;
         /* should raise exception for consistency */
@@ -2133,7 +2133,7 @@ nucomp_convert(VALUE klass, VALUE a1, VALUE a2, int raise)
         int argc;
         VALUE argv2[2];
         argv2[0] = a1;
-        if (a2 == Qundef) {
+        if (UNDEF_P(a2)) {
             argv2[1] = Qnil;
             argc = 1;
         }
diff --git a/configure.ac b/configure.ac
index 46caa99e7e39bf..a90a8ff1bb74e9 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1284,6 +1284,11 @@ dnl AC_HEADER_STDC has been checked in AC_USE_SYSTEM_EXTENSIONS
 AC_HEADER_STDBOOL
 AC_HEADER_SYS_WAIT
 
+AC_CHECK_HEADERS([afunix.h], [], [],
+[#ifdef _WIN32
+# include <winsock2.h>
+#endif
+])
 AC_CHECK_HEADERS(atomic.h)
 AC_CHECK_HEADERS(copyfile.h)
 AC_CHECK_HEADERS(direct.h)
@@ -3824,6 +3829,9 @@ AS_CASE(["${YJIT_SUPPORT}"],
         LDFLAGS="$LDFLAGS -lpthread -lc++abi"
     ])
     YJIT_OBJ='yjit.$(OBJEXT)'
+    AS_IF([test x"$YJIT_SUPPORT" != "xyes" ], [
+        AC_DEFINE_UNQUOTED(YJIT_SUPPORT, [$YJIT_SUPPORT])
+    ])
     AC_DEFINE(USE_YJIT, 1)
 ], [AC_DEFINE(USE_YJIT, 0)])
 
diff --git a/cont.c b/cont.c
index a85b7fc2d1338a..c967e57325dfdb 100644
--- a/cont.c
+++ b/cont.c
@@ -1831,7 +1831,7 @@ rollback_ensure_stack(VALUE self,rb_ensure_list_t *current,rb_ensure_entry_t *ta
     /* push ensure stack */
     for (j = 0; j < i; j++) {
         func = lookup_rollback_func(target[i - j - 1].e_proc);
-        if ((VALUE)func != Qundef) {
+        if (!UNDEF_P((VALUE)func)) {
             (*func)(target[i - j - 1].data2);
         }
     }
@@ -2058,11 +2058,11 @@ rb_fiber_initialize_kw(int argc, VALUE* argv, VALUE self, int kw_splat)
         argc = rb_scan_args_kw(kw_splat, argc, argv, ":", &options);
         rb_get_kwargs(options, fiber_initialize_keywords, 0, 2, arguments);
 
-        if (arguments[0] != Qundef) {
+        if (!UNDEF_P(arguments[0])) {
             blocking = arguments[0];
         }
 
-        if (arguments[1] != Qundef) {
+        if (!UNDEF_P(arguments[1])) {
             pool = arguments[1];
         }
     }
diff --git a/dir.c b/dir.c
index a35aace6f1d3c6..4d6d80208c169a 100644
--- a/dir.c
+++ b/dir.c
@@ -2932,7 +2932,7 @@ dir_globs(VALUE args, VALUE base, int flags)
 static VALUE
 dir_glob_option_base(VALUE base)
 {
-    if (base == Qundef || NIL_P(base)) {
+    if (UNDEF_P(base) || NIL_P(base)) {
         return Qnil;
     }
 #if USE_OPENDIR_AT
@@ -3343,7 +3343,7 @@ rb_dir_s_empty_p(VALUE obj, VALUE dirname)
 
     result = (VALUE)rb_thread_call_without_gvl(nogvl_dir_empty_p, (void *)path,
                                             RUBY_UBF_IO, 0);
-    if (result == Qundef) {
+    if (UNDEF_P(result)) {
         rb_sys_fail_path(orig);
     }
     return result;
diff --git a/doc/net-http/examples.rdoc b/doc/net-http/examples.rdoc
new file mode 100644
index 00000000000000..dd4acecda68273
--- /dev/null
+++ b/doc/net-http/examples.rdoc
@@ -0,0 +1,30 @@
+Examples here assume that <tt>net/http</tt> has been required
+(which also requires +uri+):
+
+  require 'net/http'
+
+Many code examples here use these example websites:
+
+- https://jsonplaceholder.typicode.com.
+- http://example.com.
+
+Some examples also assume these variables:
+
+  uri = URI('https://jsonplaceholder.typicode.com')
+  uri.freeze # Examples may not modify.
+  hostname = uri.hostname # => "jsonplaceholder.typicode.com"
+  port = uri.port         # => 443
+
+So that example requests may be written as:
+
+  Net::HTTP.get(uri)
+  Net::HTTP.get(hostname, '/index.html')
+  Net::HTTP.start(hostname) do |http|
+    http.get('/todos/1')
+    http.get('/todos/2')
+  end
+
+An example that needs a modified URI first duplicates +uri+, then modifies the duplicate:
+
+  _uri = uri.dup
+  _uri.path = '/todos/1'
diff --git a/enum.c b/enum.c
index 4a0403faf1afc1..d900083370932c 100644
--- a/enum.c
+++ b/enum.c
@@ -779,7 +779,7 @@ inject_i(RB_BLOCK_CALL_FUNC_ARGLIST(i, p))
 
     ENUM_WANT_SVALUE();
 
-    if (memo->v1 == Qundef) {
+    if (UNDEF_P(memo->v1)) {
         MEMO_V1_SET(memo, i);
     }
     else {
@@ -796,7 +796,7 @@ inject_op_i(RB_BLOCK_CALL_FUNC_ARGLIST(i, p))
 
     ENUM_WANT_SVALUE();
 
-    if (memo->v1 == Qundef) {
+    if (UNDEF_P(memo->v1)) {
         MEMO_V1_SET(memo, i);
     }
     else if (SYMBOL_P(name = memo->u3.value)) {
@@ -820,9 +820,9 @@ ary_inject_op(VALUE ary, VALUE init, VALUE op)
     long i, n;
 
     if (RARRAY_LEN(ary) == 0)
-        return init == Qundef ? Qnil : init;
+        return UNDEF_P(init) ? Qnil : init;
 
-    if (init == Qundef) {
+    if (UNDEF_P(init)) {
         v = RARRAY_AREF(ary, 0);
         i = 1;
         if (RARRAY_LEN(ary) == 1)
@@ -1051,7 +1051,7 @@ enum_inject(int argc, VALUE *argv, VALUE obj)
 
     memo = MEMO_NEW(init, Qnil, op);
     rb_block_call(obj, id_each, 0, 0, iter, (VALUE)memo);
-    if (memo->v1 == Qundef) return Qnil;
+    if (UNDEF_P(memo->v1)) return Qnil;
     return memo->v1;
 }
 
@@ -1677,7 +1677,7 @@ enum_any(int argc, VALUE *argv, VALUE obj)
 DEFINE_ENUMFUNCS(one)
 {
     if (RTEST(result)) {
-        if (memo->v1 == Qundef) {
+        if (UNDEF_P(memo->v1)) {
             MEMO_V1_SET(memo, Qtrue);
         }
         else if (memo->v1 == Qtrue) {
@@ -1827,7 +1827,7 @@ nmin_i(RB_BLOCK_CALL_FUNC_ARGLIST(i, _data))
     else
         cmpv = i;
 
-    if (data->limit != Qundef) {
+    if (!UNDEF_P(data->limit)) {
         int c = data->cmpfunc(&cmpv, &data->limit, data);
         if (data->rev)
             c = -c;
@@ -1962,7 +1962,7 @@ enum_one(int argc, VALUE *argv, VALUE obj)
     WARN_UNUSED_BLOCK(argc);
     rb_block_call(obj, id_each, 0, 0, ENUMFUNC(one), (VALUE)memo);
     result = memo->v1;
-    if (result == Qundef) return Qfalse;
+    if (UNDEF_P(result)) return Qfalse;
     return result;
 }
 
@@ -2037,7 +2037,7 @@ min_i(RB_BLOCK_CALL_FUNC_ARGLIST(i, args))
 
     ENUM_WANT_SVALUE();
 
-    if (memo->min == Qundef) {
+    if (UNDEF_P(memo->min)) {
         memo->min = i;
     }
     else {
@@ -2056,7 +2056,7 @@ min_ii(RB_BLOCK_CALL_FUNC_ARGLIST(i, args))
 
     ENUM_WANT_SVALUE();
 
-    if (memo->min == Qundef) {
+    if (UNDEF_P(memo->min)) {
         memo->min = i;
     }
     else {
@@ -2147,7 +2147,7 @@ enum_min(int argc, VALUE *argv, VALUE obj)
         rb_block_call(obj, id_each, 0, 0, min_i, memo);
     }
     result = m->min;
-    if (result == Qundef) return Qnil;
+    if (UNDEF_P(result)) return Qnil;
     return result;
 }
 
@@ -2163,7 +2163,7 @@ max_i(RB_BLOCK_CALL_FUNC_ARGLIST(i, args))
 
     ENUM_WANT_SVALUE();
 
-    if (memo->max == Qundef) {
+    if (UNDEF_P(memo->max)) {
         memo->max = i;
     }
     else {
@@ -2182,7 +2182,7 @@ max_ii(RB_BLOCK_CALL_FUNC_ARGLIST(i, args))
 
     ENUM_WANT_SVALUE();
 
-    if (memo->max == Qundef) {
+    if (UNDEF_P(memo->max)) {
         memo->max = i;
     }
     else {
@@ -2272,7 +2272,7 @@ enum_max(int argc, VALUE *argv, VALUE obj)
         rb_block_call(obj, id_each, 0, 0, max_i, (VALUE)memo);
     }
     result = m->max;
-    if (result == Qundef) return Qnil;
+    if (UNDEF_P(result)) return Qnil;
     return result;
 }
 
@@ -2288,7 +2288,7 @@ minmax_i_update(VALUE i, VALUE j, struct minmax_t *memo)
 {
     int n;
 
-    if (memo->min == Qundef) {
+    if (UNDEF_P(memo->min)) {
         memo->min = i;
         memo->max = j;
     }
@@ -2313,7 +2313,7 @@ minmax_i(RB_BLOCK_CALL_FUNC_ARGLIST(i, _memo))
 
     ENUM_WANT_SVALUE();
 
-    if (memo->last == Qundef) {
+    if (UNDEF_P(memo->last)) {
         memo->last = i;
         return Qnil;
     }
@@ -2340,7 +2340,7 @@ minmax_ii_update(VALUE i, VALUE j, struct minmax_t *memo)
 {
     int n;
 
-    if (memo->min == Qundef) {
+    if (UNDEF_P(memo->min)) {
         memo->min = i;
         memo->max = j;
     }
@@ -2365,7 +2365,7 @@ minmax_ii(RB_BLOCK_CALL_FUNC_ARGLIST(i, _memo))
 
     ENUM_WANT_SVALUE();
 
-    if (memo->last == Qundef) {
+    if (UNDEF_P(memo->last)) {
         memo->last = i;
         return Qnil;
     }
@@ -2430,15 +2430,15 @@ enum_minmax(VALUE obj)
     m->cmp_opt.opt_inited = 0;
     if (rb_block_given_p()) {
         rb_block_call(obj, id_each, 0, 0, minmax_ii, memo);
-        if (m->last != Qundef)
+        if (!UNDEF_P(m->last))
             minmax_ii_update(m->last, m->last, m);
     }
     else {
         rb_block_call(obj, id_each, 0, 0, minmax_i, memo);
-        if (m->last != Qundef)
+        if (!UNDEF_P(m->last))
             minmax_i_update(m->last, m->last, m);
     }
-    if (m->min != Qundef) {
+    if (!UNDEF_P(m->min)) {
         return rb_assoc_new(m->min, m->max);
     }
     return rb_assoc_new(Qnil, Qnil);
@@ -2454,7 +2454,7 @@ min_by_i(RB_BLOCK_CALL_FUNC_ARGLIST(i, args))
     ENUM_WANT_SVALUE();
 
     v = enum_yield(argc, i);
-    if (memo->v1 == Qundef) {
+    if (UNDEF_P(memo->v1)) {
         MEMO_V1_SET(memo, v);
         MEMO_V2_SET(memo, i);
     }
@@ -2529,7 +2529,7 @@ max_by_i(RB_BLOCK_CALL_FUNC_ARGLIST(i, args))
     ENUM_WANT_SVALUE();
 
     v = enum_yield(argc, i);
-    if (memo->v1 == Qundef) {
+    if (UNDEF_P(memo->v1)) {
         MEMO_V1_SET(memo, v);
         MEMO_V2_SET(memo, i);
     }
@@ -2608,7 +2608,7 @@ minmax_by_i_update(VALUE v1, VALUE v2, VALUE i1, VALUE i2, struct minmax_by_t *m
 {
     struct cmp_opt_data cmp_opt = { 0, 0 };
 
-    if (memo->min_bv == Qundef) {
+    if (UNDEF_P(memo->min_bv)) {
         memo->min_bv = v1;
         memo->max_bv = v2;
         memo->min = i1;
@@ -2638,7 +2638,7 @@ minmax_by_i(RB_BLOCK_CALL_FUNC_ARGLIST(i, _memo))
 
     vi = enum_yield(argc, i);
 
-    if (memo->last_bv == Qundef) {
+    if (UNDEF_P(memo->last_bv)) {
         memo->last_bv = vi;
         memo->last = i;
         return Qnil;
@@ -2705,7 +2705,7 @@ enum_minmax_by(VALUE obj)
     m->last_bv = Qundef;
     m->last = Qundef;
     rb_block_call(obj, id_each, 0, 0, minmax_by_i, memo);
-    if (m->last_bv != Qundef)
+    if (!UNDEF_P(m->last_bv))
         minmax_by_i_update(m->last_bv, m->last_bv, m->last, m->last, m);
     m = MEMO_FOR(struct minmax_by_t, memo);
     return rb_assoc_new(m->min, m->max);
@@ -3185,7 +3185,7 @@ zip_i(RB_BLOCK_CALL_FUNC_ARGLIST(val, memoval))
 
             v[1] = RARRAY_AREF(args, i);
             rb_rescue2(call_next, (VALUE)v, call_stop, (VALUE)v, rb_eStopIteration, (VALUE)0);
-            if (v[0] == Qundef) {
+            if (UNDEF_P(v[0])) {
                 RARRAY_ASET(args, i, Qnil);
                 v[0] = Qnil;
             }
@@ -4155,7 +4155,7 @@ slicewhen_ii(RB_BLOCK_CALL_FUNC_ARGLIST(i, _memo))
 
     ENUM_WANT_SVALUE();
 
-    if (memo->prev_elt == Qundef) {
+    if (UNDEF_P(memo->prev_elt)) {
         /* The first element */
         memo->prev_elt = i;
         memo->prev_elts = rb_ary_new3(1, i);
@@ -4395,7 +4395,7 @@ sum_iter_bignum(VALUE i, struct enum_sum_memo *memo)
 static void
 sum_iter_rational(VALUE i, struct enum_sum_memo *memo)
 {
-    if (memo->r == Qundef) {
+    if (UNDEF_P(memo->r)) {
         memo->r = i;
     }
     else {
@@ -4616,7 +4616,7 @@ enum_sum(int argc, VALUE* argv, VALUE obj)
     else {
         if (memo.n != 0)
             memo.v = rb_fix_plus(LONG2FIX(memo.n), memo.v);
-        if (memo.r != Qundef) {
+        if (!UNDEF_P(memo.r)) {
             memo.v = rb_rational_plus(memo.r, memo.v);
         }
         return memo.v;
diff --git a/enumerator.c b/enumerator.c
index 2c9858cda6d0f5..d41fcfde083f21 100644
--- a/enumerator.c
+++ b/enumerator.c
@@ -260,7 +260,7 @@ enumerator_ptr(VALUE obj)
     struct enumerator *ptr;
 
     TypedData_Get_Struct(obj, struct enumerator, &enumerator_data_type, ptr);
-    if (!ptr || ptr->obj == Qundef) {
+    if (!ptr || UNDEF_P(ptr->obj)) {
         rb_raise(rb_eArgError, "uninitialized enumerator");
     }
     return ptr;
@@ -735,7 +735,7 @@ next_ii(RB_BLOCK_CALL_FUNC_ARGLIST(i, obj))
     VALUE feedvalue = Qnil;
     VALUE args = rb_ary_new4(argc, argv);
     rb_fiber_yield(1, &args);
-    if (e->feedvalue != Qundef) {
+    if (!UNDEF_P(e->feedvalue)) {
         feedvalue = e->feedvalue;
         e->feedvalue = Qundef;
     }
@@ -840,7 +840,7 @@ enumerator_next_values(VALUE obj)
     struct enumerator *e = enumerator_ptr(obj);
     VALUE vs;
 
-    if (e->lookahead != Qundef) {
+    if (!UNDEF_P(e->lookahead)) {
         vs = e->lookahead;
         e->lookahead = Qundef;
         return vs;
@@ -901,7 +901,7 @@ enumerator_peek_values(VALUE obj)
 {
     struct enumerator *e = enumerator_ptr(obj);
 
-    if (e->lookahead == Qundef) {
+    if (UNDEF_P(e->lookahead)) {
         e->lookahead = get_next_values(obj, e);
     }
     return e->lookahead;
@@ -1025,7 +1025,7 @@ enumerator_feed(VALUE obj, VALUE v)
 {
     struct enumerator *e = enumerator_ptr(obj);
 
-    if (e->feedvalue != Qundef) {
+    if (!UNDEF_P(e->feedvalue)) {
         rb_raise(rb_eTypeError, "feed value already set");
     }
     e->feedvalue = v;
@@ -1070,7 +1070,7 @@ inspect_enumerator(VALUE obj, VALUE dummy, int recur)
 
     cname = rb_obj_class(obj);
 
-    if (!e || e->obj == Qundef) {
+    if (!e || UNDEF_P(e->obj)) {
         return rb_sprintf("#<%"PRIsVALUE": uninitialized>", rb_class_path(cname));
     }
 
@@ -1239,7 +1239,7 @@ enumerator_size(VALUE obj)
         argv = RARRAY_CONST_PTR(e->args);
     }
     size = rb_check_funcall_kw(e->size, id_call, argc, argv, e->kw_splat);
-    if (size != Qundef) return size;
+    if (!UNDEF_P(size)) return size;
     return e->size;
 }
 
@@ -1285,7 +1285,7 @@ yielder_ptr(VALUE obj)
     struct yielder *ptr;
 
     TypedData_Get_Struct(obj, struct yielder, &yielder_data_type, ptr);
-    if (!ptr || ptr->proc == Qundef) {
+    if (!ptr || UNDEF_P(ptr->proc)) {
         rb_raise(rb_eArgError, "uninitialized yielder");
     }
     return ptr;
@@ -1425,7 +1425,7 @@ generator_ptr(VALUE obj)
     struct generator *ptr;
 
     TypedData_Get_Struct(obj, struct generator, &generator_data_type, ptr);
-    if (!ptr || ptr->proc == Qundef) {
+    if (!ptr || UNDEF_P(ptr->proc)) {
         rb_raise(rb_eArgError, "uninitialized generator");
     }
     return ptr;
@@ -1529,7 +1529,7 @@ static VALUE
 enum_size(VALUE self)
 {
     VALUE r = rb_check_funcall(self, id_size, 0, 0);
-    return (r == Qundef) ? Qnil : r;
+    return UNDEF_P(r) ? Qnil : r;
 }
 
 static VALUE
@@ -1562,7 +1562,7 @@ lazy_init_iterator(RB_BLOCK_CALL_FUNC_ARGLIST(val, m))
         result = rb_yield_values2(len, nargv);
         ALLOCV_END(args);
     }
-    if (result == Qundef) rb_iter_break();
+    if (UNDEF_P(result)) rb_iter_break();
     return Qnil;
 }
 
@@ -2923,7 +2923,7 @@ producer_ptr(VALUE obj)
     struct producer *ptr;
 
     TypedData_Get_Struct(obj, struct producer, &producer_data_type, ptr);
-    if (!ptr || ptr->proc == Qundef) {
+    if (!ptr || UNDEF_P(ptr->proc)) {
         rb_raise(rb_eArgError, "uninitialized producer");
     }
     return ptr;
@@ -2978,7 +2978,7 @@ producer_each_i(VALUE obj)
     init = ptr->init;
     proc = ptr->proc;
 
-    if (init == Qundef) {
+    if (UNDEF_P(init)) {
         curr = Qnil;
     }
     else {
@@ -3109,7 +3109,7 @@ enum_chain_ptr(VALUE obj)
     struct enum_chain *ptr;
 
     TypedData_Get_Struct(obj, struct enum_chain, &enum_chain_data_type, ptr);
-    if (!ptr || ptr->enums == Qundef) {
+    if (!ptr || UNDEF_P(ptr->enums)) {
         rb_raise(rb_eArgError, "uninitialized chain");
     }
     return ptr;
@@ -3302,7 +3302,7 @@ inspect_enum_chain(VALUE obj, VALUE dummy, int recur)
 
     TypedData_Get_Struct(obj, struct enum_chain, &enum_chain_data_type, ptr);
 
-    if (!ptr || ptr->enums == Qundef) {
+    if (!ptr || UNDEF_P(ptr->enums)) {
         return rb_sprintf("#<%"PRIsVALUE": uninitialized>", rb_class_path(klass));
     }
 
@@ -3431,7 +3431,7 @@ enum_product_ptr(VALUE obj)
     struct enum_product *ptr;
 
     TypedData_Get_Struct(obj, struct enum_product, &enum_product_data_type, ptr);
-    if (!ptr || ptr->enums == Qundef) {
+    if (!ptr || UNDEF_P(ptr->enums)) {
         rb_raise(rb_eArgError, "uninitialized product");
     }
     return ptr;
@@ -3642,7 +3642,7 @@ inspect_enum_product(VALUE obj, VALUE dummy, int recur)
 
     TypedData_Get_Struct(obj, struct enum_product, &enum_product_data_type, ptr);
 
-    if (!ptr || ptr->enums == Qundef) {
+    if (!ptr || UNDEF_P(ptr->enums)) {
         return rb_sprintf("#<%"PRIsVALUE": uninitialized>", rb_class_path(klass));
     }
 
diff --git a/error.c b/error.c
index 67e81d08a0f193..0ff4b8d6d8e082 100644
--- a/error.c
+++ b/error.c
@@ -1005,7 +1005,7 @@ rb_check_type(VALUE x, int t)
 {
     int xt;
 
-    if (RB_UNLIKELY(x == Qundef)) {
+    if (RB_UNLIKELY(UNDEF_P(x))) {
         rb_bug(UNDEF_LEAKED);
     }
 
@@ -1026,7 +1026,7 @@ rb_check_type(VALUE x, int t)
 void
 rb_unexpected_type(VALUE x, int t)
 {
-    if (RB_UNLIKELY(x == Qundef)) {
+    if (RB_UNLIKELY(UNDEF_P(x))) {
         rb_bug(UNDEF_LEAKED);
     }
 
@@ -1228,7 +1228,7 @@ VALUE
 rb_get_message(VALUE exc)
 {
     VALUE e = rb_check_funcall(exc, id_message, 0, 0);
-    if (e == Qundef) return Qnil;
+    if (UNDEF_P(e)) return Qnil;
     if (!RB_TYPE_P(e, T_STRING)) e = rb_check_string_type(e);
     return e;
 }
@@ -1243,7 +1243,7 @@ rb_get_detailed_message(VALUE exc, VALUE opt)
     else {
         e = rb_check_funcall_kw(exc, id_detailed_message, 1, &opt, 1);
     }
-    if (e == Qundef) return Qnil;
+    if (UNDEF_P(e)) return Qnil;
     if (!RB_TYPE_P(e, T_STRING)) e = rb_check_string_type(e);
     return e;
 }
@@ -1635,15 +1635,15 @@ exc_equal(VALUE exc, VALUE obj)
         int state;
 
         obj = rb_protect(try_convert_to_exception, obj, &state);
-        if (state || obj == Qundef) {
+        if (state || UNDEF_P(obj)) {
             rb_set_errinfo(Qnil);
             return Qfalse;
         }
         if (rb_obj_class(exc) != rb_obj_class(obj)) return Qfalse;
         mesg = rb_check_funcall(obj, id_message, 0, 0);
-        if (mesg == Qundef) return Qfalse;
+        if (UNDEF_P(mesg)) return Qfalse;
         backtrace = rb_check_funcall(obj, id_backtrace, 0, 0);
-        if (backtrace == Qundef) return Qfalse;
+        if (UNDEF_P(backtrace)) return Qfalse;
     }
     else {
         mesg = rb_attr_get(obj, id_mesg);
@@ -1746,7 +1746,7 @@ exit_success_p(VALUE exc)
 static VALUE
 err_init_recv(VALUE exc, VALUE recv)
 {
-    if (recv != Qundef) rb_ivar_set(exc, id_recv, recv);
+    if (!UNDEF_P(recv)) rb_ivar_set(exc, id_recv, recv);
     return exc;
 }
 
@@ -2090,7 +2090,7 @@ name_err_mesg_to_str(VALUE obj)
             break;
           default:
             d = rb_protect(name_err_mesg_receiver_name, obj, &state);
-            if (state || d == Qundef || NIL_P(d))
+            if (state || UNDEF_P(d) || NIL_P(d))
                 d = rb_protect(rb_inspect, obj, &state);
             if (state) {
                 rb_set_errinfo(Qnil);
@@ -2145,7 +2145,7 @@ name_err_receiver(VALUE self)
     VALUE *ptr, recv, mesg;
 
     recv = rb_ivar_lookup(self, id_recv, Qundef);
-    if (recv != Qundef) return recv;
+    if (!UNDEF_P(recv)) return recv;
 
     mesg = rb_attr_get(self, id_mesg);
     if (!rb_typeddata_is_kind_of(mesg, &name_err_mesg_data_type)) {
@@ -2203,7 +2203,7 @@ key_err_receiver(VALUE self)
     VALUE recv;
 
     recv = rb_ivar_lookup(self, id_receiver, Qundef);
-    if (recv != Qundef) return recv;
+    if (!UNDEF_P(recv)) return recv;
     rb_raise(rb_eArgError, "no receiver is available");
 }
 
@@ -2220,7 +2220,7 @@ key_err_key(VALUE self)
     VALUE key;
 
     key = rb_ivar_lookup(self, id_key, Qundef);
-    if (key != Qundef) return key;
+    if (!UNDEF_P(key)) return key;
     rb_raise(rb_eArgError, "no key is available");
 }
 
@@ -2258,7 +2258,7 @@ key_err_initialize(int argc, VALUE *argv, VALUE self)
         keywords[1] = id_key;
         rb_get_kwargs(options, keywords, 0, numberof(values), values);
         for (i = 0; i < numberof(values); ++i) {
-            if (values[i] != Qundef) {
+            if (!UNDEF_P(values[i])) {
                 rb_ivar_set(self, keywords[i], values[i]);
             }
         }
@@ -2280,7 +2280,7 @@ no_matching_pattern_key_err_matchee(VALUE self)
     VALUE matchee;
 
     matchee = rb_ivar_lookup(self, id_matchee, Qundef);
-    if (matchee != Qundef) return matchee;
+    if (!UNDEF_P(matchee)) return matchee;
     rb_raise(rb_eArgError, "no matchee is available");
 }
 
@@ -2297,7 +2297,7 @@ no_matching_pattern_key_err_key(VALUE self)
     VALUE key;
 
     key = rb_ivar_lookup(self, id_key, Qundef);
-    if (key != Qundef) return key;
+    if (!UNDEF_P(key)) return key;
     rb_raise(rb_eArgError, "no key is available");
 }
 
@@ -2324,7 +2324,7 @@ no_matching_pattern_key_err_initialize(int argc, VALUE *argv, VALUE self)
         keywords[1] = id_key;
         rb_get_kwargs(options, keywords, 0, numberof(values), values);
         for (i = 0; i < numberof(values); ++i) {
-            if (values[i] != Qundef) {
+            if (!UNDEF_P(values[i])) {
                 rb_ivar_set(self, keywords[i], values[i]);
             }
         }
diff --git a/eval.c b/eval.c
index 826ae1456e5826..c95c3fb9edaf5e 100644
--- a/eval.c
+++ b/eval.c
@@ -514,7 +514,7 @@ exc_setup_message(const rb_execution_context_t *ec, VALUE mesg, VALUE *cause)
         nocause = 0;
         nocircular = 1;
     }
-    if (*cause == Qundef) {
+    if (UNDEF_P(*cause)) {
         if (nocause) {
             *cause = Qnil;
             nocircular = 1;
@@ -530,7 +530,7 @@ exc_setup_message(const rb_execution_context_t *ec, VALUE mesg, VALUE *cause)
         rb_raise(rb_eTypeError, "exception object expected");
     }
 
-    if (!nocircular && !NIL_P(*cause) && *cause != Qundef && *cause != mesg) {
+    if (!nocircular && !NIL_P(*cause) && !UNDEF_P(*cause) && *cause != mesg) {
         VALUE c = *cause;
         while (!NIL_P(c = rb_attr_get(c, id_cause))) {
             if (c == mesg) {
@@ -549,18 +549,18 @@ setup_exception(rb_execution_context_t *ec, int tag, volatile VALUE mesg, VALUE
     const char *file = rb_source_location_cstr(&line);
     const char *const volatile file0 = file;
 
-    if ((file && !NIL_P(mesg)) || (cause != Qundef))  {
+    if ((file && !NIL_P(mesg)) || !UNDEF_P(cause))  {
         volatile int state = 0;
 
         EC_PUSH_TAG(ec);
         if (EC_EXEC_TAG() == TAG_NONE && !(state = rb_ec_set_raised(ec))) {
             VALUE bt = rb_get_backtrace(mesg);
-            if (!NIL_P(bt) || cause == Qundef) {
+            if (!NIL_P(bt) || UNDEF_P(cause)) {
                 if (OBJ_FROZEN(mesg)) {
                     mesg = rb_obj_dup(mesg);
                 }
             }
-            if (cause != Qundef && !THROW_DATA_P(cause)) {
+            if (!UNDEF_P(cause) && !THROW_DATA_P(cause)) {
                 exc_setup_cause(mesg, cause);
             }
             if (NIL_P(bt)) {
@@ -633,7 +633,7 @@ setup_exception(rb_execution_context_t *ec, int tag, volatile VALUE mesg, VALUE
 void
 rb_ec_setup_exception(const rb_execution_context_t *ec, VALUE mesg, VALUE cause)
 {
-    if (cause == Qundef) {
+    if (UNDEF_P(cause)) {
         cause = get_ec_errinfo(ec);
     }
     if (cause != mesg) {
@@ -728,7 +728,7 @@ rb_f_raise(int argc, VALUE *argv)
 
     argc = extract_raise_opts(argc, argv, opts);
     if (argc == 0) {
-        if (*cause != Qundef) {
+        if (!UNDEF_P(*cause)) {
             rb_raise(rb_eArgError, "only cause is given with no arguments");
         }
         err = get_errinfo();
@@ -804,7 +804,7 @@ make_exception(int argc, const VALUE *argv, int isstr)
     if (NIL_P(mesg)) {
         mesg = rb_check_funcall(argv[0], idException, argc != 1, &argv[1]);
     }
-    if (mesg == Qundef) {
+    if (UNDEF_P(mesg)) {
         rb_raise(rb_eTypeError, "exception class/object expected");
     }
     if (!rb_obj_is_kind_of(mesg, rb_eException)) {
diff --git a/eval_error.c b/eval_error.c
index 6582b805aa07dd..dfb3e6b6762e5d 100644
--- a/eval_error.c
+++ b/eval_error.c
@@ -306,7 +306,7 @@ rb_error_write(VALUE errinfo, VALUE emesg, VALUE errat, VALUE str, VALUE opt, VA
     if (NIL_P(errinfo))
         return;
 
-    if (errat == Qundef) {
+    if (UNDEF_P(errat)) {
         errat = Qnil;
     }
     eclass = CLASS_OF(errinfo);
@@ -358,7 +358,7 @@ rb_ec_error_print(rb_execution_context_t * volatile ec, volatile VALUE errinfo)
     if (EC_EXEC_TAG() == TAG_NONE) {
         errat = rb_get_backtrace(errinfo);
     }
-    if (emesg == Qundef) {
+    if (UNDEF_P(emesg)) {
         emesg = Qnil;
         emesg = rb_get_detailed_message(errinfo, opt);
     }
diff --git a/ext/extmk.rb b/ext/extmk.rb
index 73ee71fd376241..cc560be1f22c93 100755
--- a/ext/extmk.rb
+++ b/ext/extmk.rb
@@ -721,6 +721,8 @@ def initialize(src)
     mf.puts "ECHO1 = $(V:1=@:)"
     mf.puts "ECHO = $(ECHO1:0=@echo)"
     mf.puts "MFLAGS = -$(MAKEFLAGS)" if $nmake
+    mf.puts "override MFLAGS := $(filter-out -j%,$(MFLAGS))" if $gnumake
+    mf.puts "ext_build_dir = #{File.dirname($command_output)}"
     mf.puts
 
     def mf.macro(name, values, max = 70)
@@ -763,6 +765,7 @@ def mf.macro(name, values, max = 70)
     mf.macro "SUBMAKEOPTS", submakeopts
     mf.macro "NOTE_MESG", %w[$(RUBY) $(top_srcdir)/tool/lib/colorize.rb skip]
     mf.macro "NOTE_NAME", %w[$(RUBY) $(top_srcdir)/tool/lib/colorize.rb fail]
+    %w[RM RMDIRS RMDIR RMALL].each {|w| mf.macro w, [RbConfig::CONFIG[w]]}
     mf.puts
     targets = %w[all install static install-so install-rb clean distclean realclean]
     targets.each do |tgt|
@@ -797,16 +800,20 @@ def mf.macro(name, values, max = 70)
       exts.each do |d|
         d = d[0..-2]
         t = "#{d}#{tgt}"
-        if  /^(dist|real)?clean$/ =~ tgt
+        if clean = /^(dist|real)?clean$/.match(tgt)
           deps = exts.select {|e|e.start_with?(d)}.map {|e|"#{e[0..-2]}#{tgt}"} - [t]
-          pd = ' ' + deps.join(' ') unless deps.empty?
+          pd = [' clean-local', *deps].join(' ')
         else
           pext = File.dirname(d)
           pd = " #{pext}/#{tgt}" if exts.include?("#{pext}/.")
         end
         mf.puts "#{t}:#{pd}\n\t$(Q)#{submake} $(MFLAGS) V=$(V) $(@F)"
+        if clean and clean.begin(1)
+          mf.puts "\t$(Q)$(RM) $(ext_build_dir)/exts.mk\n\t$(Q)$(RMDIRS) -p $(@D)"
+        end
       end
     end
+    mf.puts "\n""clean-local:\n\t$(Q)$(RM) $(ext_build_dir)/*~ $(ext_build_dir)/*.bak $(ext_build_dir)/core"
     mf.puts "\n""extso:\n"
     mf.puts "\t@echo EXTSO=$(EXTSO)"
 
diff --git a/ext/socket/extconf.rb b/ext/socket/extconf.rb
index 8998bb5c2f2869..73bbc8e6871436 100644
--- a/ext/socket/extconf.rb
+++ b/ext/socket/extconf.rb
@@ -316,6 +316,7 @@ def test_recvmsg_with_msg_peek_creates_fds(headers)
   netpacket/packet.h
   net/ethernet.h
   sys/un.h
+  afunix.h
   ifaddrs.h
   sys/ioctl.h
   sys/sockio.h
diff --git a/ext/socket/init.c b/ext/socket/init.c
index ac28f5c3293377..557d4374a51e0c 100644
--- a/ext/socket/init.c
+++ b/ext/socket/init.c
@@ -209,7 +209,7 @@ rsock_s_recvfrom(VALUE socket, int argc, VALUE *argv, enum sock_recv_type from)
         else
             return rb_assoc_new(str, Qnil);
 
-#ifdef HAVE_SYS_UN_H
+#ifdef HAVE_TYPE_STRUCT_SOCKADDR_UN
       case RECV_UNIX:
         return rb_assoc_new(str, rsock_unixaddr(&arg.buf.un, arg.alen));
 #endif
diff --git a/ext/socket/lib/socket.rb b/ext/socket/lib/socket.rb
index d756a32a5aafb0..c96e48e8f0429c 100644
--- a/ext/socket/lib/socket.rb
+++ b/ext/socket/lib/socket.rb
@@ -197,7 +197,7 @@ def listen(backlog=Socket::SOMAXCONN)
     sock = Socket.new(self.pfamily, self.socktype, self.protocol)
     begin
       sock.ipv6only! if self.ipv6?
-      sock.setsockopt(:SOCKET, :REUSEADDR, 1)
+      sock.setsockopt(:SOCKET, :REUSEADDR, 1) unless self.pfamily == Socket::PF_UNIX
       sock.bind(self)
       sock.listen(backlog)
     rescue Exception
diff --git a/ext/socket/option.c b/ext/socket/option.c
index 2dbe6379c43674..0d818d0c704520 100644
--- a/ext/socket/option.c
+++ b/ext/socket/option.c
@@ -670,10 +670,10 @@ rb_if_indextoname(const char *succ_prefix, const char *fail_prefix, unsigned int
 {
 #if defined(HAVE_IF_INDEXTONAME)
     char ifbuf[IFNAMSIZ];
-    if (if_indextoname(ifindex, ifbuf) == NULL)
-        return snprintf(buf, len, "%s%u", fail_prefix, ifindex);
-    else
+    if (if_indextoname(ifindex, ifbuf))
         return snprintf(buf, len, "%s%s", succ_prefix, ifbuf);
+    else
+        return snprintf(buf, len, "%s%u", fail_prefix, ifindex);
 #else
 #   ifndef IFNAMSIZ
 #       define IFNAMSIZ (sizeof(unsigned int)*3+1)
@@ -1229,7 +1229,7 @@ sockopt_inspect(VALUE self)
         else
             rb_str_catf(ret, " optname:%d", optname);
     }
-#ifdef HAVE_SYS_UN_H
+#ifdef HAVE_TYPE_STRUCT_SOCKADDR_UN
     else if (family == AF_UNIX) {
         rb_str_catf(ret, " level:%d", level);
 
@@ -1393,7 +1393,7 @@ sockopt_inspect(VALUE self)
         }
         break;
 
-#ifdef HAVE_SYS_UN_H
+#ifdef HAVE_TYPE_STRUCT_SOCKADDR_UN
       case AF_UNIX:
         switch (level) {
           case 0:
diff --git a/ext/socket/raddrinfo.c b/ext/socket/raddrinfo.c
index 636d1edda3296c..269edc4dadd526 100644
--- a/ext/socket/raddrinfo.c
+++ b/ext/socket/raddrinfo.c
@@ -644,7 +644,7 @@ rsock_ipaddr(struct sockaddr *sockaddr, socklen_t sockaddrlen, int norevlookup)
     return ary;
 }
 
-#ifdef HAVE_SYS_UN_H
+#ifdef HAVE_TYPE_STRUCT_SOCKADDR_UN
 static long
 unixsocket_len(const struct sockaddr_un *su, socklen_t socklen)
 {
@@ -1017,7 +1017,7 @@ addrinfo_list_new(VALUE node, VALUE service, VALUE family, VALUE socktype, VALUE
 }
 
 
-#ifdef HAVE_SYS_UN_H
+#ifdef HAVE_TYPE_STRUCT_SOCKADDR_UN
 static void
 init_unix_addrinfo(rb_addrinfo_t *rai, VALUE path, int socktype)
 {
@@ -1146,7 +1146,7 @@ addrinfo_initialize(int argc, VALUE *argv, VALUE self)
             break;
           }
 
-#ifdef HAVE_SYS_UN_H
+#ifdef HAVE_TYPE_STRUCT_SOCKADDR_UN
           case AF_UNIX: /* ["AF_UNIX", "/tmp/sock"] */
           {
             VALUE path = rb_ary_entry(sockaddr_ary, 1);
@@ -1286,7 +1286,7 @@ rsock_inspect_sockaddr(struct sockaddr *sockaddr_arg, socklen_t socklen, VALUE r
           }
 #endif
 
-#ifdef HAVE_SYS_UN_H
+#ifdef HAVE_TYPE_STRUCT_SOCKADDR_UN
           case AF_UNIX:
           {
             struct sockaddr_un *addr = &sockaddr->un;
@@ -1622,7 +1622,7 @@ addrinfo_mdump(VALUE self)
     afamily = rb_id2str(id);
 
     switch(afamily_int) {
-#ifdef HAVE_SYS_UN_H
+#ifdef HAVE_TYPE_STRUCT_SOCKADDR_UN
       case AF_UNIX:
       {
         sockaddr = rb_str_new(rai->addr.un.sun_path, rai_unixsocket_len(rai));
@@ -1715,7 +1715,7 @@ addrinfo_mload(VALUE self, VALUE ary)
 
     v = rb_ary_entry(ary, 1);
     switch(afamily) {
-#ifdef HAVE_SYS_UN_H
+#ifdef HAVE_TYPE_STRUCT_SOCKADDR_UN
       case AF_UNIX:
       {
         struct sockaddr_un uaddr;
@@ -2343,7 +2343,7 @@ addrinfo_ipv6_to_ipv4(VALUE self)
 
 #endif
 
-#ifdef HAVE_SYS_UN_H
+#ifdef HAVE_TYPE_STRUCT_SOCKADDR_UN
 /*
  * call-seq:
  *   addrinfo.unix_path => path
@@ -2491,7 +2491,7 @@ addrinfo_s_udp(VALUE self, VALUE host, VALUE port)
             INT2NUM(PF_UNSPEC), INT2NUM(SOCK_DGRAM), INT2NUM(IPPROTO_UDP), INT2FIX(0));
 }
 
-#ifdef HAVE_SYS_UN_H
+#ifdef HAVE_TYPE_STRUCT_SOCKADDR_UN
 
 /*
  * call-seq:
@@ -2629,7 +2629,7 @@ rsock_init_addrinfo(void)
     rb_define_singleton_method(rb_cAddrinfo, "ip", addrinfo_s_ip, 1);
     rb_define_singleton_method(rb_cAddrinfo, "tcp", addrinfo_s_tcp, 2);
     rb_define_singleton_method(rb_cAddrinfo, "udp", addrinfo_s_udp, 2);
-#ifdef HAVE_SYS_UN_H
+#ifdef HAVE_TYPE_STRUCT_SOCKADDR_UN
     rb_define_singleton_method(rb_cAddrinfo, "unix", addrinfo_s_unix, -1);
 #endif
 
@@ -2670,7 +2670,7 @@ rsock_init_addrinfo(void)
     rb_define_method(rb_cAddrinfo, "ipv6_to_ipv4", addrinfo_ipv6_to_ipv4, 0);
 #endif
 
-#ifdef HAVE_SYS_UN_H
+#ifdef HAVE_TYPE_STRUCT_SOCKADDR_UN
     rb_define_method(rb_cAddrinfo, "unix_path", addrinfo_unix_path, 0);
 #endif
 
diff --git a/ext/socket/rubysocket.h b/ext/socket/rubysocket.h
index 9ec893ee8ccc6f..5f803ba0da3c6f 100644
--- a/ext/socket/rubysocket.h
+++ b/ext/socket/rubysocket.h
@@ -33,6 +33,9 @@
 #endif
 
 #ifdef _WIN32
+#  include <winsock2.h>
+#  include <ws2tcpip.h>
+#  include <iphlpapi.h>
 #  if defined(_MSC_VER)
 #    undef HAVE_TYPE_STRUCT_SOCKADDR_DL
 #  endif
@@ -69,6 +72,11 @@
 #  include <sys/un.h>
 #endif
 
+#ifdef HAVE_AFUNIX_H
+// Windows doesn't have sys/un.h, but it does have afunix.h just to be special:
+#  include <afunix.h>
+#endif
+
 #if defined(HAVE_FCNTL)
 #  ifdef HAVE_SYS_SELECT_H
 #    include <sys/select.h>
@@ -268,7 +276,7 @@ extern VALUE rb_cIPSocket;
 extern VALUE rb_cTCPSocket;
 extern VALUE rb_cTCPServer;
 extern VALUE rb_cUDPSocket;
-#ifdef HAVE_SYS_UN_H
+#ifdef HAVE_TYPE_STRUCT_SOCKADDR_UN
 extern VALUE rb_cUNIXSocket;
 extern VALUE rb_cUNIXServer;
 #endif
@@ -336,7 +344,7 @@ VALUE rsock_sockaddr_obj(struct sockaddr *addr, socklen_t len);
 
 int rsock_revlookup_flag(VALUE revlookup, int *norevlookup);
 
-#ifdef HAVE_SYS_UN_H
+#ifdef HAVE_TYPE_STRUCT_SOCKADDR_UN
 VALUE rsock_unixpath_str(struct sockaddr_un *sockaddr, socklen_t len);
 VALUE rsock_unixaddr(struct sockaddr_un *sockaddr, socklen_t len);
 socklen_t rsock_unix_sockaddr_len(VALUE path);
diff --git a/ext/socket/socket.c b/ext/socket/socket.c
index 5cf083506252e9..eb74f7a936a3f3 100644
--- a/ext/socket/socket.c
+++ b/ext/socket/socket.c
@@ -1383,7 +1383,7 @@ sock_s_unpack_sockaddr_in(VALUE self, VALUE addr)
     return rb_assoc_new(INT2NUM(ntohs(sockaddr->sin_port)), host);
 }
 
-#ifdef HAVE_SYS_UN_H
+#ifdef HAVE_TYPE_STRUCT_SOCKADDR_UN
 
 /*
  * call-seq:
@@ -1471,7 +1471,7 @@ sockaddr_len(struct sockaddr *addr)
         return (socklen_t)sizeof(struct sockaddr_in6);
 #endif
 
-#ifdef HAVE_SYS_UN_H
+#ifdef HAVE_TYPE_STRUCT_SOCKADDR_UN
       case AF_UNIX:
         return (socklen_t)sizeof(struct sockaddr_un);
 #endif
@@ -2020,7 +2020,7 @@ Init_socket(void)
     rb_define_singleton_method(rb_cSocket, "sockaddr_in", sock_s_pack_sockaddr_in, 2);
     rb_define_singleton_method(rb_cSocket, "pack_sockaddr_in", sock_s_pack_sockaddr_in, 2);
     rb_define_singleton_method(rb_cSocket, "unpack_sockaddr_in", sock_s_unpack_sockaddr_in, 1);
-#ifdef HAVE_SYS_UN_H
+#ifdef HAVE_TYPE_STRUCT_SOCKADDR_UN
     rb_define_singleton_method(rb_cSocket, "sockaddr_un", sock_s_pack_sockaddr_un, 1);
     rb_define_singleton_method(rb_cSocket, "pack_sockaddr_un", sock_s_pack_sockaddr_un, 1);
     rb_define_singleton_method(rb_cSocket, "unpack_sockaddr_un", sock_s_unpack_sockaddr_un, 1);
diff --git a/ext/socket/unixserver.c b/ext/socket/unixserver.c
index 3a899cca1fbbad..0ea5ac083c3ca8 100644
--- a/ext/socket/unixserver.c
+++ b/ext/socket/unixserver.c
@@ -10,7 +10,7 @@
 
 #include "rubysocket.h"
 
-#ifdef HAVE_SYS_UN_H
+#ifdef HAVE_TYPE_STRUCT_SOCKADDR_UN
 /*
  * call-seq:
  *   UNIXServer.new(path) => unixserver
@@ -101,7 +101,7 @@ unix_sysaccept(VALUE server)
 void
 rsock_init_unixserver(void)
 {
-#ifdef HAVE_SYS_UN_H
+#ifdef HAVE_TYPE_STRUCT_SOCKADDR_UN
     /*
      * Document-class: UNIXServer < UNIXSocket
      *
diff --git a/ext/socket/unixsocket.c b/ext/socket/unixsocket.c
index ecffbd4e922be8..26ab76fc9fb7e6 100644
--- a/ext/socket/unixsocket.c
+++ b/ext/socket/unixsocket.c
@@ -10,7 +10,7 @@
 
 #include "rubysocket.h"
 
-#ifdef HAVE_SYS_UN_H
+#ifdef HAVE_TYPE_STRUCT_SOCKADDR_UN
 struct unixsock_arg {
     struct sockaddr_un *sockaddr;
     socklen_t sockaddrlen;
@@ -42,6 +42,10 @@ unixsock_path_value(VALUE path)
             return name;             /* ignore encoding */
         }
     }
+#endif
+#ifdef _WIN32
+    /* UNIXSocket requires UTF-8 per spec. */
+    path = rb_str_export_to_enc(path, rb_utf8_encoding());
 #endif
     return rb_get_path(path);
 }
@@ -571,7 +575,7 @@ unix_s_socketpair(int argc, VALUE *argv, VALUE klass)
 void
 rsock_init_unixsocket(void)
 {
-#ifdef HAVE_SYS_UN_H
+#ifdef HAVE_TYPE_STRUCT_SOCKADDR_UN
     /*
      * Document-class: UNIXSocket < BasicSocket
      *
diff --git a/file.c b/file.c
index 93f5898ccde0b8..10eb1081e328a9 100644
--- a/file.c
+++ b/file.c
@@ -115,6 +115,8 @@ int flock(int, int);
 # define link(f, t)      rb_w32_ulink((f), (t))
 # undef unlink
 # define unlink(p)       rb_w32_uunlink(p)
+# undef readlink
+# define readlink(f, t, l)    rb_w32_ureadlink((f), (t), (l))
 # undef rename
 # define rename(f, t)    rb_w32_urename((f), (t))
 # undef symlink
@@ -1763,8 +1765,8 @@ rb_file_socket_p(VALUE obj, VALUE fname)
 
     if (rb_stat(fname, &st) < 0) return Qfalse;
     if (S_ISSOCK(st.st_mode)) return Qtrue;
-
 #endif
+
     return Qfalse;
 }
 
@@ -3152,7 +3154,6 @@ rb_file_s_readlink(VALUE klass, VALUE path)
     return rb_readlink(path, rb_filesystem_encoding());
 }
 
-#ifndef _WIN32
 struct readlink_arg {
     const char *path;
     char *buf;
@@ -3208,7 +3209,6 @@ rb_readlink(VALUE path, rb_encoding *enc)
 
     return v;
 }
-#endif
 #else
 #define rb_file_s_readlink rb_f_notimplement
 #endif
@@ -5600,6 +5600,7 @@ rb_stat_init(VALUE obj, VALUE fname)
     if (STAT(StringValueCStr(fname), &st) == -1) {
         rb_sys_fail_path(fname);
     }
+
     if (DATA_PTR(obj)) {
         xfree(DATA_PTR(obj));
         DATA_PTR(obj) = NULL;
diff --git a/gc.c b/gc.c
index ef0532e3256d57..8817538194a7d4 100644
--- a/gc.c
+++ b/gc.c
@@ -3135,6 +3135,12 @@ rb_class_instance_allocate_internal(VALUE klass, VALUE flags, bool wb_protected)
 #endif
 
     VALUE obj = newobj_of(klass, flags, 0, 0, 0, wb_protected, size);
+    RUBY_ASSERT(rb_shape_get_shape(obj)->type == SHAPE_ROOT ||
+            rb_shape_get_shape(obj)->type == SHAPE_INITIAL_CAPACITY);
+
+    // Set the shape to the specific T_OBJECT shape which is always
+    // SIZE_POOL_COUNT away from the root shape.
+    ROBJECT_SET_SHAPE_ID(obj, ROBJECT_SHAPE_ID(obj) + SIZE_POOL_COUNT);
 
 #if RUBY_DEBUG
     VALUE *ptr = ROBJECT_IVPTR(obj);
@@ -4568,7 +4574,7 @@ run_single_final(VALUE cmd, VALUE objid)
 static void
 warn_exception_in_finalizer(rb_execution_context_t *ec, VALUE final)
 {
-    if (final != Qundef && !NIL_P(ruby_verbose)) {
+    if (!UNDEF_P(final) && !NIL_P(ruby_verbose)) {
         VALUE errinfo = ec->errinfo;
         rb_warn("Exception in finalizer %+"PRIsVALUE, final);
         rb_ec_error_print(ec, errinfo);
@@ -5038,7 +5044,7 @@ id2ref(VALUE objid)
         }
     }
 
-    if ((orig = id2ref_obj_tbl(objspace, objid)) != Qundef &&
+    if (!UNDEF_P(orig = id2ref_obj_tbl(objspace, objid)) &&
         is_live_object(objspace, orig)) {
 
         if (!rb_multi_ractor_p() || rb_ractor_shareable_p(orig)) {
@@ -7785,7 +7791,7 @@ gc_mark_stacked_objects(rb_objspace_t *objspace, int incremental, size_t count)
 #endif
 
     while (pop_mark_stack(mstack, &obj)) {
-        if (obj == Qundef) continue; /* skip */
+        if (UNDEF_P(obj)) continue; /* skip */
 
         if (RGENGC_CHECK_MODE && !RVALUE_MARKED(obj)) {
             rb_bug("gc_mark_stacked_objects: %s is not marked.", obj_info(obj));
@@ -10492,7 +10498,7 @@ gc_ref_update_object(rb_objspace_t *objspace, VALUE v)
         }
         ptr = ROBJECT(v)->as.ary;
         size_t size_pool_shape_id = size_pool_idx_for_size(embed_size);
-        rb_shape_t * initial_shape = rb_shape_get_shape_by_id((shape_id_t)size_pool_shape_id);
+        rb_shape_t * initial_shape = rb_shape_get_shape_by_id((shape_id_t)size_pool_shape_id + SIZE_POOL_COUNT);
         rb_shape_t * new_shape = rb_shape_rebuild_shape(initial_shape, rb_shape_get_shape(v));
         rb_shape_set_shape(v, new_shape);
     }
@@ -13301,7 +13307,7 @@ wmap_finalize(RB_BLOCK_CALL_FUNC_ARGLIST(objid, self))
 
     TypedData_Get_Struct(self, struct weakmap, &weakmap_type, w);
     /* Get reference from object id. */
-    if ((obj = id2ref_obj_tbl(&rb_objspace, objid)) == Qundef) {
+    if (UNDEF_P(obj = id2ref_obj_tbl(&rb_objspace, objid))) {
         rb_bug("wmap_finalize: objid is not found.");
     }
 
@@ -13592,14 +13598,14 @@ static VALUE
 wmap_aref(VALUE self, VALUE key)
 {
     VALUE obj = wmap_lookup(self, key);
-    return obj != Qundef ? obj : Qnil;
+    return !UNDEF_P(obj) ? obj : Qnil;
 }
 
 /* Returns +true+ if +key+ is registered */
 static VALUE
 wmap_has_key(VALUE self, VALUE key)
 {
-    return RBOOL(wmap_lookup(self, key) != Qundef);
+    return RBOOL(!UNDEF_P(wmap_lookup(self, key)));
 }
 
 /* Returns the number of referenced objects */
diff --git a/hash.c b/hash.c
index 876d8b9efc70c0..a577e7798584d6 100644
--- a/hash.c
+++ b/hash.c
@@ -111,7 +111,7 @@ rb_any_cmp(VALUE a, VALUE b)
         RB_TYPE_P(b, T_STRING) && RBASIC(b)->klass == rb_cString) {
         return rb_str_hash_cmp(a, b);
     }
-    if (a == Qundef || b == Qundef) return -1;
+    if (UNDEF_P(a) || UNDEF_P(b)) return -1;
     if (SYMBOL_P(a) && SYMBOL_P(b)) {
         return a != b;
     }
@@ -195,7 +195,7 @@ obj_any_hash(VALUE obj)
 {
     VALUE hval = rb_check_funcall_basic_kw(obj, id_hash, rb_mKernel, 0, 0, 0);
 
-    if (hval == Qundef) {
+    if (UNDEF_P(hval)) {
         hval = rb_exec_recursive_outer_mid(hash_recursive, obj, 0, id_hash);
     }
 
@@ -437,7 +437,7 @@ ar_cleared_entry(VALUE hash, unsigned int index)
          * so you need to check key == Qundef
          */
         ar_table_pair *pair = RHASH_AR_TABLE_REF(hash, index);
-        return pair->key == Qundef;
+        return UNDEF_P(pair->key);
     }
     else {
         return FALSE;
@@ -517,8 +517,8 @@ hash_verify_(VALUE hash, const char *file, int line)
                 ar_table_pair *pair = RHASH_AR_TABLE_REF(hash, i);
                 k = pair->key;
                 v = pair->val;
-                HASH_ASSERT(k != Qundef);
-                HASH_ASSERT(v != Qundef);
+                HASH_ASSERT(!UNDEF_P(k));
+                HASH_ASSERT(!UNDEF_P(v));
                 n++;
             }
         }
@@ -2076,7 +2076,7 @@ rb_hash_default_value(VALUE hash, VALUE key)
     if (LIKELY(rb_method_basic_definition_p(CLASS_OF(hash), id_default))) {
         VALUE ifnone = RHASH_IFNONE(hash);
         if (!FL_TEST(hash, RHASH_PROC_DEFAULT)) return ifnone;
-        if (key == Qundef) return Qnil;
+        if (UNDEF_P(key)) return Qnil;
         return call_default_proc(ifnone, hash, key);
     }
     else {
@@ -2402,7 +2402,7 @@ rb_hash_delete(VALUE hash, VALUE key)
 {
     VALUE deleted_value = rb_hash_delete_entry(hash, key);
 
-    if (deleted_value != Qundef) { /* likely pass */
+    if (!UNDEF_P(deleted_value)) { /* likely pass */
         return deleted_value;
     }
     else {
@@ -2445,7 +2445,7 @@ rb_hash_delete_m(VALUE hash, VALUE key)
     rb_hash_modify_check(hash);
     val = rb_hash_delete_entry(hash, key);
 
-    if (val != Qundef) {
+    if (!UNDEF_P(val)) {
         return val;
     }
     else {
@@ -2502,7 +2502,7 @@ rb_hash_shift(VALUE hash)
         }
         else {
             rb_hash_foreach(hash, shift_i_safe, (VALUE)&var);
-            if (var.key != Qundef) {
+            if (!UNDEF_P(var.key)) {
                 rb_hash_delete_entry(hash, var.key);
                 return rb_assoc_new(var.key, var.val);
             }
@@ -2517,7 +2517,7 @@ rb_hash_shift(VALUE hash)
         }
         else {
             rb_hash_foreach(hash, shift_i_safe, (VALUE)&var);
-            if (var.key != Qundef) {
+            if (!UNDEF_P(var.key)) {
                 rb_hash_delete_entry(hash, var.key);
                 return rb_assoc_new(var.key, var.val);
             }
@@ -2658,7 +2658,7 @@ rb_hash_slice(int argc, VALUE *argv, VALUE hash)
     for (i = 0; i < argc; i++) {
         key = argv[i];
         value = rb_hash_lookup2(hash, key, Qundef);
-        if (value != Qundef)
+        if (!UNDEF_P(value))
             rb_hash_aset(result, key, value);
     }
 
@@ -3181,7 +3181,7 @@ transform_keys_hash_i(VALUE key, VALUE value, VALUE transarg)
     struct transform_keys_args *p = (void *)transarg;
     VALUE trans = p->trans, result = p->result;
     VALUE new_key = rb_hash_lookup2(trans, key, Qundef);
-    if (new_key == Qundef) {
+    if (UNDEF_P(new_key)) {
         if (p->block_given)
             new_key = rb_yield(key);
         else
@@ -3302,7 +3302,7 @@ rb_hash_transform_keys_bang(int argc, VALUE *argv, VALUE hash)
             if (!trans) {
                 new_key = rb_yield(key);
             }
-            else if ((new_key = rb_hash_lookup2(trans, key, Qundef)) != Qundef) {
+            else if (!UNDEF_P(new_key = rb_hash_lookup2(trans, key, Qundef))) {
                 /* use the transformed key */
             }
             else if (block_given) {
@@ -4195,7 +4195,7 @@ rb_hash_assoc(VALUE hash, VALUE key)
         ensure_arg.hash = hash;
         ensure_arg.orighash = orighash;
         value = rb_ensure(lookup2_call, (VALUE)&args, reset_hash_type, (VALUE)&ensure_arg);
-        if (value != Qundef) return rb_assoc_new(key, value);
+        if (!UNDEF_P(value)) return rb_assoc_new(key, value);
     }
 
     args[0] = key;
@@ -4608,7 +4608,7 @@ hash_le_i(VALUE key, VALUE value, VALUE arg)
 {
     VALUE *args = (VALUE *)arg;
     VALUE v = rb_hash_lookup2(args[0], key, Qundef);
-    if (v != Qundef && rb_equal(value, v)) return ST_CONTINUE;
+    if (!UNDEF_P(v) && rb_equal(value, v)) return ST_CONTINUE;
     args[1] = Qfalse;
     return ST_STOP;
 }
diff --git a/include/ruby/internal/special_consts.h b/include/ruby/internal/special_consts.h
index ed2428e087d070..dc0a6b41d6bad6 100644
--- a/include/ruby/internal/special_consts.h
+++ b/include/ruby/internal/special_consts.h
@@ -326,7 +326,7 @@ RBIMPL_ATTR_ARTIFICIAL()
 static inline bool
 RB_SPECIAL_CONST_P(VALUE obj)
 {
-    return RB_IMMEDIATE_P(obj) || ! RB_TEST(obj);
+    return RB_IMMEDIATE_P(obj) || obj == RUBY_Qfalse;
 }
 
 RBIMPL_ATTR_CONST()
diff --git a/include/ruby/win32.h b/include/ruby/win32.h
index 93e6183ed990a2..197eb8a8027ee4 100644
--- a/include/ruby/win32.h
+++ b/include/ruby/win32.h
@@ -18,11 +18,6 @@ RUBY_SYMBOL_EXPORT_BEGIN
  *
  */
 
-/*
- * Definitions for NT port of Perl
- */
-
-
 /*
  * Ok now we can include the normal include files.
  */
@@ -302,7 +297,6 @@ extern DWORD  rb_w32_osver(void);
 extern int rb_w32_uchown(const char *, int, int);
 extern int rb_w32_ulink(const char *, const char *);
 extern ssize_t rb_w32_ureadlink(const char *, char *, size_t);
-extern ssize_t rb_w32_wreadlink(const WCHAR *, WCHAR *, size_t);
 extern int rb_w32_usymlink(const char *src, const char *link);
 extern int gettimeofday(struct timeval *, struct timezone *);
 extern int clock_gettime(clockid_t, struct timespec *);
@@ -393,6 +387,7 @@ scalb(double a, long b)
 #endif
 
 #define S_IFLNK 0xa000
+#define S_IFSOCK 0xc000
 
 /*
  * define this so we can do inplace editing
diff --git a/inits.c b/inits.c
index 3c2b11c851df43..17fa0afbb677f4 100644
--- a/inits.c
+++ b/inits.c
@@ -99,6 +99,7 @@ rb_call_builtin_inits(void)
     BUILTIN(warning);
     BUILTIN(array);
     BUILTIN(kernel);
+    BUILTIN(symbol);
     BUILTIN(timev);
     BUILTIN(thread_sync);
     BUILTIN(yjit);
diff --git a/io.c b/io.c
index 63a96bf2b80a68..8787c4f804fac5 100644
--- a/io.c
+++ b/io.c
@@ -1255,7 +1255,7 @@ rb_io_read_memory(rb_io_t *fptr, void *buf, size_t count)
     if (scheduler != Qnil) {
         VALUE result = rb_fiber_scheduler_io_read_memory(scheduler, fptr->self, buf, count, 0);
 
-        if (result != Qundef) {
+        if (!UNDEF_P(result)) {
             return rb_fiber_scheduler_io_result_apply(result);
         }
     }
@@ -1288,7 +1288,7 @@ rb_io_write_memory(rb_io_t *fptr, const void *buf, size_t count)
     if (scheduler != Qnil) {
         VALUE result = rb_fiber_scheduler_io_write_memory(scheduler, fptr->self, buf, count, 0);
 
-        if (result != Qundef) {
+        if (!UNDEF_P(result)) {
             return rb_fiber_scheduler_io_result_apply(result);
         }
     }
@@ -1323,7 +1323,7 @@ rb_writev_internal(rb_io_t *fptr, const struct iovec *iov, int iovcnt)
         for (int i = 0; i < iovcnt; i += 1) {
             VALUE result = rb_fiber_scheduler_io_write_memory(scheduler, fptr->self, iov[i].iov_base, iov[i].iov_len, 0);
 
-            if (result != Qundef) {
+            if (!UNDEF_P(result)) {
                 return rb_fiber_scheduler_io_result_apply(result);
             }
         }
@@ -1424,7 +1424,7 @@ rb_io_wait(VALUE io, VALUE events, VALUE timeout)
     struct timeval tv_storage;
     struct timeval *tv = NULL;
 
-    if (timeout == Qnil || timeout == Qundef) {
+    if (timeout == Qnil || UNDEF_P(timeout)) {
         timeout = fptr->timeout;
     }
 
@@ -3352,7 +3352,7 @@ io_read_memory_call(VALUE arg)
     if (scheduler != Qnil) {
         VALUE result = rb_fiber_scheduler_io_read_memory(scheduler, iis->fptr->self, iis->buf, iis->capa, 0);
 
-        if (result != Qundef) {
+        if (!UNDEF_P(result)) {
             // This is actually returned as a pseudo-VALUE and later cast to a long:
             return (VALUE)rb_fiber_scheduler_io_result_apply(result);
         }
@@ -3972,7 +3972,7 @@ extract_getline_opts(VALUE opts, struct getline_arg *args)
             kwds[0] = rb_intern_const("chomp");
         }
         rb_get_kwargs(opts, kwds, 0, -2, &vchomp);
-        chomp = (vchomp != Qundef) && RTEST(vchomp);
+        chomp = (!UNDEF_P(vchomp)) && RTEST(vchomp);
     }
     args->chomp = chomp;
 }
@@ -5445,7 +5445,7 @@ fptr_finalize_flush(rb_io_t *fptr, int noraise, int keepgvl,
     //     VALUE scheduler = rb_fiber_scheduler_current();
     //     if (scheduler != Qnil) {
     //         VALUE result = rb_fiber_scheduler_io_close(scheduler, fptr->self);
-    //         if (result != Qundef) done = 1;
+    //         if (!UNDEF_P(result)) done = 1;
     //     }
     // }
 
@@ -5704,7 +5704,7 @@ static VALUE
 io_close(VALUE io)
 {
     VALUE closed = rb_check_funcall(io, rb_intern("closed?"), 0, 0);
-    if (closed != Qundef && RTEST(closed)) return io;
+    if (!UNDEF_P(closed) && RTEST(closed)) return io;
     rb_rescue2(io_call_close, io, ignore_closed_stream, io,
                rb_eIOError, (VALUE)0);
     return io;
@@ -6622,21 +6622,21 @@ rb_io_extract_encoding_option(VALUE opt, rb_encoding **enc_p, rb_encoding **enc2
         v = rb_hash_lookup2(opt, sym_extenc, Qundef);
         if (v != Qnil) extenc = v;
         v = rb_hash_lookup2(opt, sym_intenc, Qundef);
-        if (v != Qundef) intenc = v;
+        if (!UNDEF_P(v)) intenc = v;
     }
-    if ((extenc != Qundef || intenc != Qundef) && !NIL_P(encoding)) {
+    if ((!UNDEF_P(extenc) || !UNDEF_P(intenc)) && !NIL_P(encoding)) {
         if (!NIL_P(ruby_verbose)) {
             int idx = rb_to_encoding_index(encoding);
             if (idx >= 0) encoding = rb_enc_from_encoding(rb_enc_from_index(idx));
             rb_warn("Ignoring encoding parameter '%"PRIsVALUE"': %s_encoding is used",
-                    encoding, extenc == Qundef ? "internal" : "external");
+                    encoding, UNDEF_P(extenc) ? "internal" : "external");
         }
         encoding = Qnil;
     }
-    if (extenc != Qundef && !NIL_P(extenc)) {
+    if (!UNDEF_P(extenc) && !NIL_P(extenc)) {
         extencoding = rb_to_encoding(extenc);
     }
-    if (intenc != Qundef) {
+    if (!UNDEF_P(intenc)) {
         if (NIL_P(intenc)) {
             /* internal_encoding: nil => no transcoding */
             intencoding = (rb_encoding *)Qnil;
@@ -6669,7 +6669,7 @@ rb_io_extract_encoding_option(VALUE opt, rb_encoding **enc_p, rb_encoding **enc2
             rb_io_ext_int_to_encs(rb_to_encoding(encoding), NULL, enc_p, enc2_p, 0);
         }
     }
-    else if (extenc != Qundef || intenc != Qundef) {
+    else if (!UNDEF_P(extenc) || !UNDEF_P(intenc)) {
         extracted = 1;
         rb_io_ext_int_to_encs(extencoding, intencoding, enc_p, enc2_p, 0);
     }
@@ -9724,7 +9724,7 @@ io_wait(int argc, VALUE *argv, VALUE io)
             if (RB_SYMBOL_P(argv[i])) {
                 events |= wait_mode_sym(argv[i]);
             }
-            else if (timeout == Qundef) {
+            else if (UNDEF_P(timeout)) {
                 rb_time_interval(timeout = argv[i]);
             }
             else {
@@ -9732,7 +9732,7 @@ io_wait(int argc, VALUE *argv, VALUE io)
             }
         }
 
-        if (timeout == Qundef) timeout = Qnil;
+        if (UNDEF_P(timeout)) timeout = Qnil;
 
         if (events == 0) {
             events = RUBY_IO_READABLE;
@@ -10918,7 +10918,7 @@ rb_f_select(int argc, VALUE *argv, VALUE obj)
     if (scheduler != Qnil) {
         // It's optionally supported.
         VALUE result = rb_fiber_scheduler_io_selectv(scheduler, argc, argv);
-        if (result != Qundef) return result;
+        if (!UNDEF_P(result)) return result;
     }
 
     VALUE timeout;
@@ -14042,7 +14042,7 @@ static void
 argf_block_call(ID mid, int argc, VALUE *argv, VALUE argf)
 {
     VALUE ret = ARGF_block_call(mid, argc, argv, argf_block_call_i, argf);
-    if (ret != Qundef) ARGF.next_p = 1;
+    if (!UNDEF_P(ret)) ARGF.next_p = 1;
 }
 
 static VALUE
@@ -14058,7 +14058,7 @@ static void
 argf_block_call_line(ID mid, int argc, VALUE *argv, VALUE argf)
 {
     VALUE ret = ARGF_block_call(mid, argc, argv, argf_block_call_line_i, argf);
-    if (ret != Qundef) ARGF.next_p = 1;
+    if (!UNDEF_P(ret)) ARGF.next_p = 1;
 }
 
 /*
diff --git a/io_buffer.c b/io_buffer.c
index cbf51250c4b22d..dc9d613524d5ea 100644
--- a/io_buffer.c
+++ b/io_buffer.c
@@ -2384,7 +2384,7 @@ rb_io_buffer_read(VALUE self, VALUE io, size_t length, size_t offset)
     if (scheduler != Qnil) {
         VALUE result = rb_fiber_scheduler_io_read(scheduler, io, self, SIZET2NUM(length), SIZET2NUM(offset));
 
-        if (result != Qundef) {
+        if (!UNDEF_P(result)) {
             return result;
         }
     }
@@ -2501,7 +2501,7 @@ rb_io_buffer_pread(VALUE self, VALUE io, rb_off_t from, size_t length, size_t of
     if (scheduler != Qnil) {
         VALUE result = rb_fiber_scheduler_io_pread(scheduler, io, OFFT2NUM(from), self, SIZET2NUM(length), SIZET2NUM(offset));
 
-        if (result != Qundef) {
+        if (!UNDEF_P(result)) {
             return result;
         }
     }
@@ -2574,7 +2574,7 @@ rb_io_buffer_write(VALUE self, VALUE io, size_t length, size_t offset)
     if (scheduler != Qnil) {
         VALUE result = rb_fiber_scheduler_io_write(scheduler, io, self, SIZET2NUM(length), SIZET2NUM(offset));
 
-        if (result != Qundef) {
+        if (!UNDEF_P(result)) {
             return result;
         }
     }
@@ -2668,7 +2668,7 @@ rb_io_buffer_pwrite(VALUE self, VALUE io, rb_off_t from, size_t length, size_t o
     if (scheduler != Qnil) {
         VALUE result = rb_fiber_scheduler_io_pwrite(scheduler, io, OFFT2NUM(from), self, SIZET2NUM(length), SIZET2NUM(offset));
 
-        if (result != Qundef) {
+        if (!UNDEF_P(result)) {
             return result;
         }
     }
diff --git a/iseq.c b/iseq.c
index 1d0c96dba17d59..a2e79cd55badcf 100644
--- a/iseq.c
+++ b/iseq.c
@@ -331,7 +331,7 @@ rb_iseq_update_references(rb_iseq_t *iseq)
 
             for (j = 0; i < body->param.keyword->num; i++, j++) {
                 VALUE obj = body->param.keyword->default_values[j];
-                if (obj != Qundef) {
+                if (!UNDEF_P(obj)) {
                     body->param.keyword->default_values[j] = rb_gc_location(obj);
                 }
             }
@@ -2916,7 +2916,7 @@ iseq_data_to_ary(const rb_iseq_t *iseq)
             }
             for (j=0; i<keyword->num; i++, j++) {
                 VALUE key = rb_ary_new_from_args(1, ID2SYM(keyword->table[i]));
-                if (keyword->default_values[j] != Qundef) {
+                if (!UNDEF_P(keyword->default_values[j])) {
                     rb_ary_push(key, keyword->default_values[j]);
                 }
                 rb_ary_push(keywords, key);
diff --git a/lib/irb.rb b/lib/irb.rb
index 04009664efd47a..0a856d3929ce98 100644
--- a/lib/irb.rb
+++ b/lib/irb.rb
@@ -53,6 +53,50 @@
 #
 #   :include: ./irb/lc/help-message
 #
+# == Commands
+#
+# The following commands are available on IRB.
+#
+# * cwws
+#   * Show the current workspace.
+# * cb, cws, chws
+#   * Change the current workspace to an object.
+# * bindings, workspaces
+#   * Show workspaces.
+# * pushb, pushws
+#   * Push an object to the workspace stack.
+# * popb, popws
+#   * Pop a workspace from the workspace stack.
+# * load
+#   * Load a Ruby file.
+# * require
+#   * Require a Ruby file.
+# * source
+#   * Loads a given file in the current session.
+# * irb
+#   * Start a child IRB.
+# * jobs
+#   * List of current sessions.
+# * fg
+#   * Switches to the session of the given number.
+# * kill
+#   * Kills the session with the given number.
+# * help
+#   * Enter the mode to look up RI documents.
+# * irb_info
+#   * Show information about IRB.
+# * ls
+#   * Show methods, constants, and variables.
+#     -g [query] or -G [query] allows you to filter out the output.
+# * measure
+#   * measure enables the mode to measure processing time. measure :off disables it.
+# * $, show_source
+#   * Show the source code of a given method or constant.
+# * @, whereami
+#   * Show the source code around binding.irb again.
+# * debug
+#   * Start the debugger of debug.gem.
+#
 # == Configuration
 #
 # IRB reads a personal initialization file when it's invoked.
@@ -93,9 +137,9 @@
 #
 # === Autocompletion
 #
-# To enable autocompletion for irb, add the following to your +.irbrc+:
+# To disable autocompletion for irb, add the following to your +.irbrc+:
 #
-#     require 'irb/completion'
+#     IRB.conf[:USE_AUTOCOMPLETE] = false
 #
 # === History
 #
@@ -434,6 +478,17 @@ def initialize(workspace = nil, input_method = nil)
       @scanner = RubyLex.new
     end
 
+    # A hook point for `debug` command's TracePoint after :IRB_EXIT as well as its clean-up
+    def debug_break
+      # it means the debug command is executed
+      if defined?(DEBUGGER__) && DEBUGGER__.respond_to?(:capture_frames_without_irb)
+        # after leaving this initial breakpoint, revert the capture_frames patch
+        DEBUGGER__.singleton_class.send(:alias_method, :capture_frames, :capture_frames_without_irb)
+        # and remove the redundant method
+        DEBUGGER__.singleton_class.send(:undef_method, :capture_frames_without_irb)
+      end
+    end
+
     def run(conf = IRB.conf)
       conf[:IRB_RC].call(context) if conf[:IRB_RC]
       conf[:MAIN_CONTEXT] = context
@@ -598,11 +653,7 @@ def handle_exception(exc)
 
       if exc.backtrace
         order = nil
-        if '2.5.0' == RUBY_VERSION
-          # Exception#full_message doesn't have keyword arguments.
-          message = exc.full_message # the same of (highlight: true, order: bottom)
-          order = :bottom
-        elsif '2.5.1' <= RUBY_VERSION && RUBY_VERSION < '3.0.0'
+        if RUBY_VERSION < '3.0.0'
           if STDOUT.tty?
             message = exc.full_message(order: :bottom)
             order = :bottom
@@ -928,12 +979,13 @@ class Binding
   #
   #
   # See IRB@IRB+Usage for more information.
-  def irb
+  def irb(show_code: true)
     IRB.setup(source_location[0], argv: [])
     workspace = IRB::WorkSpace.new(self)
-    STDOUT.print(workspace.code_around_binding)
+    STDOUT.print(workspace.code_around_binding) if show_code
     binding_irb = IRB::Irb.new(workspace)
     binding_irb.context.irb_path = File.expand_path(source_location[0])
     binding_irb.run(IRB.conf)
+    binding_irb.debug_break
   end
 end
diff --git a/lib/irb/cmd/debug.rb b/lib/irb/cmd/debug.rb
new file mode 100644
index 00000000000000..d43e060c67a2df
--- /dev/null
+++ b/lib/irb/cmd/debug.rb
@@ -0,0 +1,96 @@
+require_relative "nop"
+
+module IRB
+  # :stopdoc:
+
+  module ExtendCommand
+    class Debug < Nop
+      BINDING_IRB_FRAME_REGEXPS = [
+        '<internal:prelude>',
+        binding.method(:irb).source_location.first,
+      ].map { |file| /\A#{Regexp.escape(file)}:\d+:in `irb'\z/ }
+      IRB_DIR = File.expand_path('..', __dir__)
+
+      def execute(*args)
+        unless binding_irb?
+          puts "`debug` command is only available when IRB is started with binding.irb"
+          return
+        end
+
+        unless setup_debugger
+          puts <<~MSG
+            You need to install the debug gem before using this command.
+            If you use `bundle exec`, please add `gem "debug"` into your Gemfile.
+          MSG
+          return
+        end
+
+        # To make debugger commands like `next` or `continue` work without asking
+        # the user to quit IRB after that, we need to exit IRB first and then hit
+        # a TracePoint on #debug_break.
+        file, lineno = IRB::Irb.instance_method(:debug_break).source_location
+        DEBUGGER__::SESSION.add_line_breakpoint(file, lineno + 1, oneshot: true, hook_call: false)
+        # exit current Irb#run call
+        throw :IRB_EXIT
+      end
+
+      private
+
+      def binding_irb?
+        caller.any? do |frame|
+          BINDING_IRB_FRAME_REGEXPS.any? do |regexp|
+            frame.match?(regexp)
+          end
+        end
+      end
+
+      def setup_debugger
+        unless defined?(DEBUGGER__::SESSION)
+          begin
+            require "debug/session"
+          rescue LoadError # debug.gem is not written in Gemfile
+            return false unless load_bundled_debug_gem
+          end
+          DEBUGGER__.start(nonstop: true)
+        end
+
+        unless DEBUGGER__.respond_to?(:capture_frames_without_irb)
+          DEBUGGER__.singleton_class.send(:alias_method, :capture_frames_without_irb, :capture_frames)
+
+          def DEBUGGER__.capture_frames(*args)
+            frames = capture_frames_without_irb(*args)
+            frames.reject! do |frame|
+              frame.realpath&.start_with?(IRB_DIR) || frame.path == "<internal:prelude>"
+            end
+            frames
+          end
+        end
+
+        true
+      end
+
+      # This is used when debug.gem is not written in Gemfile. Even if it's not
+      # installed by `bundle install`, debug.gem is installed by default because
+      # it's a bundled gem. This method tries to activate and load that.
+      def load_bundled_debug_gem
+        # Discover latest debug.gem under GEM_PATH
+        debug_gem = Gem.paths.path.map { |path| Dir.glob("#{path}/gems/debug-*") }.flatten.select do |path|
+          File.basename(path).match?(/\Adebug-\d+\.\d+\.\d+\z/)
+        end.sort_by do |path|
+          Gem::Version.new(File.basename(path).delete_prefix('debug-'))
+        end.last
+        return false unless debug_gem
+
+        # Attempt to forcibly load the bundled gem
+        $LOAD_PATH << "#{debug_gem}/lib"
+        begin
+          require "debug/session"
+          puts "Loaded #{File.basename(debug_gem)}"
+          true
+        rescue LoadError
+          false
+        end
+      end
+    end
+  end
+end
diff --git a/lib/irb/completion.rb b/lib/irb/completion.rb
index b41d5de35e3119..34640e17f974c3 100644
--- a/lib/irb/completion.rb
+++ b/lib/irb/completion.rb
@@ -361,6 +361,7 @@ def self.retrieve_completion_data(input, bind: IRB.conf[:MAIN_CONTEXT].workspace
           to_ignore = ignored_modules
           ObjectSpace.each_object(Module){|m|
             next if (to_ignore.include?(m) rescue true)
+            next unless m.respond_to?(:instance_methods) # JRuby has modules that represent java packages. They don't include many common ruby methods
             candidates.concat m.instance_methods(false).collect{|x| x.to_s}
           }
           candidates.sort!
diff --git a/lib/irb/context.rb b/lib/irb/context.rb
index 72c74f081dca0e..c5d98772b89187 100644
--- a/lib/irb/context.rb
+++ b/lib/irb/context.rb
@@ -49,10 +49,13 @@ def initialize(irb, workspace = nil, input_method = nil)
       if IRB.conf.has_key?(:USE_MULTILINE)
         @use_multiline = IRB.conf[:USE_MULTILINE]
       elsif IRB.conf.has_key?(:USE_RELINE) # backward compatibility
+        warn <<~MSG.strip
+          USE_RELINE is deprecated, please use USE_MULTILINE instead.
+        MSG
         @use_multiline = IRB.conf[:USE_RELINE]
       elsif IRB.conf.has_key?(:USE_REIDLINE)
         warn <<~MSG.strip
-          USE_REIDLINE is deprecated, please use USE_RELINE instead.
+          USE_REIDLINE is deprecated, please use USE_MULTILINE instead.
         MSG
         @use_multiline = IRB.conf[:USE_REIDLINE]
       else
diff --git a/lib/irb/ext/save-history.rb b/lib/irb/ext/save-history.rb
index 2135184dba37a9..a74b89f8c33978 100644
--- a/lib/irb/ext/save-history.rb
+++ b/lib/irb/ext/save-history.rb
@@ -73,7 +73,7 @@ def load_history
         open(history_file, "r:#{IRB.conf[:LC_MESSAGES].encoding}") do |f|
           f.each { |l|
             l = l.chomp
-            if self.class == ReidlineInputMethod and history.last&.end_with?("\\")
+            if self.class == RelineInputMethod and history.last&.end_with?("\\")
               history.last.delete_suffix!("\\")
               history.last << "\n" << l
             else
diff --git a/lib/irb/extend-command.rb b/lib/irb/extend-command.rb
index acc23c9920f1ca..94fd9c8bb4fab6 100644
--- a/lib/irb/extend-command.rb
+++ b/lib/irb/extend-command.rb
@@ -116,6 +116,10 @@ def irb_context
         [:kill, OVERRIDE_PRIVATE_ONLY],
       ],
 
+      [
+        :irb_debug, :Debug, "cmd/debug",
+        [:debug, NO_OVERRIDE],
+      ],
       [
         :irb_help, :Help, "cmd/help",
         [:help, NO_OVERRIDE],
@@ -161,26 +165,7 @@ def self.load_command(command)
       nil
     end
 
-    # Installs the default irb commands:
-    #
-    # +irb_current_working_workspace+::   Context#main
-    # +irb_change_workspace+::            Context#change_workspace
-    # +irb_workspaces+::                  Context#workspaces
-    # +irb_push_workspace+::              Context#push_workspace
-    # +irb_pop_workspace+::               Context#pop_workspace
-    # +irb_load+::                        #irb_load
-    # +irb_require+::                     #irb_require
-    # +irb_source+::                      IrbLoader#source_file
-    # +irb+::                             IRB.irb
-    # +irb_jobs+::                        JobManager
-    # +irb_fg+::                          JobManager#switch
-    # +irb_kill+::                        JobManager#kill
-    # +irb_help+::                        IRB@Command+line+options
-    # +irb_info+::                        #inspect
-    # +irb_ls+::                          Output#dump
-    # +irb_measure+::                     IRB::unset_measure_callback
-    # +irb_show_source+::                 #find_source, #show_source
-    # +irb_whereami+::                    Workspace#code_around_binding
+    # Installs the default irb commands.
     def self.install_extend_commands
       for args in @EXTEND_COMMANDS
         def_extend_command(*args)
diff --git a/lib/irb/init.rb b/lib/irb/init.rb
index 8c9d473b74d84c..831d7d811ae9c9 100644
--- a/lib/irb/init.rb
+++ b/lib/irb/init.rb
@@ -260,8 +260,20 @@ def IRB.parse_opts(argv: ::ARGV)
       when "--nosingleline", "--noreadline"
         @CONF[:USE_SINGLELINE] = false
       when "--multiline", "--reidline"
+        if opt == "--reidline"
+          warn <<~MSG.strip
+            --reidline is deprecated, please use --multiline instead.
+          MSG
+        end
+
         @CONF[:USE_MULTILINE] = true
       when "--nomultiline", "--noreidline"
+        if opt == "--noreidline"
+          warn <<~MSG.strip
+            --noreidline is deprecated, please use --nomultiline instead.
+          MSG
+        end
+
         @CONF[:USE_MULTILINE] = false
       when /^--extra-doc-dir(?:=(.+))?/
         opt = $1 || argv.shift
diff --git a/lib/irb/input-method.rb b/lib/irb/input-method.rb
index 5f13971a4350be..94805731956b50 100644
--- a/lib/irb/input-method.rb
+++ b/lib/irb/input-method.rb
@@ -461,7 +461,7 @@ def encoding
     # For debug message
     def inspect
       config = Reline::Config.new
-      str = "ReidlineInputMethod with Reline #{Reline::VERSION}"
+      str = "RelineInputMethod with Reline #{Reline::VERSION}"
       if config.respond_to?(:inputrc_path)
         inputrc_path = File.expand_path(config.inputrc_path)
       else
diff --git a/lib/irb/irb.gemspec b/lib/irb/irb.gemspec
index d44393804328f4..c3e8a4dc585cf4 100644
--- a/lib/irb/irb.gemspec
+++ b/lib/irb/irb.gemspec
@@ -34,7 +34,7 @@ Gem::Specification.new do |spec|
   spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
   spec.require_paths = ["lib"]
 
-  spec.required_ruby_version = Gem::Requirement.new(">= 2.5")
+  spec.required_ruby_version = Gem::Requirement.new(">= 2.6")
 
   spec.add_dependency "reline", ">= 0.3.0"
 end
diff --git a/lib/irb/version.rb b/lib/irb/version.rb
index 38fe36728ba497..2bb3aa2c99b3cb 100644
--- a/lib/irb/version.rb
+++ b/lib/irb/version.rb
@@ -11,7 +11,7 @@
 #
 
 module IRB # :nodoc:
-  VERSION = "1.4.2"
+  VERSION = "1.4.3"
   @RELEASE_VERSION = VERSION
-  @LAST_UPDATE_DATE = "2022-10-03"
+  @LAST_UPDATE_DATE = "2022-11-17"
 end
diff --git a/lib/mjit/c_pointer.rb b/lib/mjit/c_pointer.rb
index 7f64a8ac8f4906..aadf80e804e86d 100644
--- a/lib/mjit/c_pointer.rb
+++ b/lib/mjit/c_pointer.rb
@@ -282,12 +282,16 @@ def initialize(addr, width, offset)
 
       # Dereference
       def *
-        if @width != 1
-          raise NotImplementedError.new("Non-1 width is not implemented yet")
-        end
         byte = Fiddle::Pointer.new(@addr)[0, Fiddle::SIZEOF_CHAR].unpack('c').first
-        bit = 1 & (byte >> @offset)
-        bit == 1
+        if @width == 1
+          bit = (1 & (byte >> @offset))
+          bit == 1
+        elsif @width <= 8 && @offset == 0
+          bitmask = @width.times.map { |i| 1 << i }.sum
+          byte & bitmask
+        else
+          raise NotImplementedError.new("not-implemented bit field access: width=#{@width} offset=#{@offset}")
+        end
       end
 
       # @param width [Integer]
diff --git a/lib/mjit/compiler.rb b/lib/mjit/compiler.rb
index 3ccdc1c925d62b..806e7f55c49c03 100644
--- a/lib/mjit/compiler.rb
+++ b/lib/mjit/compiler.rb
@@ -1,6 +1,4 @@
 module RubyVM::MJIT
-  ROBJECT_EMBED_LEN_MAX = C.ROBJECT_EMBED_LEN_MAX
-
   UNSUPPORTED_INSNS = [
     :defineclass, # low priority
   ]
@@ -45,9 +43,9 @@ def compile(f, iseq, funcname, id)
       C.fprintf(f, "\n} // end of #{funcname}\n")
 
       return success
-    rescue => e # Should rb_rescue be called in C?
+    rescue Exception => e # should we use rb_rescue in C instead?
       if C.mjit_opts.warnings || C.mjit_opts.verbose > 0
-        $stderr.puts e.full_message
+        $stderr.puts "MJIT error: #{e.full_message}"
       end
       return false
     end
diff --git a/lib/net/http.rb b/lib/net/http.rb
index 16137cebf22d12..f07586e656031e 100644
--- a/lib/net/http.rb
+++ b/lib/net/http.rb
@@ -32,110 +32,237 @@ class HTTPBadResponse < StandardError; end
   class HTTPHeaderSyntaxError < StandardError; end
   # :startdoc:
 
-  # == An HTTP client API for Ruby.
+  # \Class \Net::HTTP provides a rich library that implements the client
+  # in a client-server model that uses the \HTTP request-response protocol.
+  # For information about \HTTP, see
+  #
+  # - {Hypertext Transfer Protocol}[https://en.wikipedia.org/wiki/Hypertext_Transfer_Protocol].
+  # - {Technical overview}[https://en.wikipedia.org/wiki/Hypertext_Transfer_Protocol#Technical_overview].
+  #
+  # Note: If you are performing only a few GET requests, consider using
+  # {OpenURI}[rdoc-ref:OpenURI];
+  # otherwise, read on.
+  #
+  # == Synopsis
+  #
+  # If you are already familiar with \HTTP, this synopsis may be helpful.
+  #
+  # {Session}[rdoc-ref:Net::HTTP@Sessions] with multiple requests for
+  # {HTTP methods}[https://en.wikipedia.org/wiki/Hypertext_Transfer_Protocol#Request_methods]:
+  #
+  #   Net::HTTP.start(hostname) do |http|
+  #     # Session started automatically before block execution.
+  #     http.get(path_or_uri, headers = {})
+  #     http.head(path_or_uri, headers = {})
+  #     http.post(path_or_uri, data, headers = {})  # Can also have a block.
+  #     http.put(path_or_uri, data, headers = {})
+  #     http.delete(path_or_uri, headers = {Depth: 'Infinity'})
+  #     http.options(path_or_uri, headers = {})
+  #     http.trace(path_or_uri, headers = {})
+  #     http.patch(path_or_uri, data, headers = {}) # Can also have a block.
+  #     # Session finished automatically at block exit.
+  #   end
   #
-  # Net::HTTP provides a rich library which can be used to build HTTP
-  # user-agents.  For more details about HTTP see
-  # [RFC2616](http://www.ietf.org/rfc/rfc2616.txt).
+  # {Session}[rdoc-ref:Net::HTTP@Sessions] with multiple requests for
+  # {WebDAV methods}[https://en.wikipedia.org/wiki/WebDAV#Implementation]:
+  #
+  #   Net::HTTP.start(hostname) do |http|
+  #     # Session started automatically before block execution.
+  #     http.copy(path_or_uri, headers = {})
+  #     http.lock(path_or_uri, body, headers = {})
+  #     http.mkcol(path_or_uri, body = nil, headers = {})
+  #     http.move(path_or_uri, headers = {})
+  #     http.propfind(path_or_uri, body = nil, headers = {'Depth' => '0'})
+  #     http.proppatch(path_or_uri, body, headers = {})
+  #     http.unlock(path_or_uri, body, headers = {})
+  #     # Session finished automatically at block exit.
+  #   end
   #
-  # Net::HTTP is designed to work closely with URI.  URI::HTTP#host,
-  # URI::HTTP#port and URI::HTTP#request_uri are designed to work with
-  # Net::HTTP.
+  # Each of the following methods automatically starts and finishes
+  # a {session}[rdoc-ref:Net::HTTP@Sessions] that sends a single request:
   #
-  # If you are only performing a few GET requests you should try OpenURI.
+  #   # Return string response body.
+  #   Net::HTTP.get(hostname, path, port = 80)
+  #   Net::HTTP.get(uri, headers = {}, port = 80)
   #
-  # == Simple Examples
+  #   # Write string response body to $stdout.
+  #   Net::HTTP.get_print(hostname, path_or_uri, port = 80)
+  #   Net::HTTP.get_print(uri, headers = {}, port = 80)
   #
-  # All examples assume you have loaded Net::HTTP with:
+  #   # Return response as Net::HTTPResponse object.
+  #   Net::HTTP.get_response(hostname, path_or_uri, port = 80)
+  #   Net::HTTP.get_response(uri, headers = {}, port = 80)
   #
-  #   require 'net/http'
+  #   Net::HTTP.post(uri, data, headers = {})
+  #   Net::HTTP.post_form(uri, params)
   #
-  # This will also require 'uri' so you don't need to require it separately.
+  # == About the Examples
   #
-  # The Net::HTTP methods in the following section do not persist
-  # connections.  They are not recommended if you are performing many HTTP
-  # requests.
+  # :include: doc/net-http/examples.rdoc
   #
-  # === GET
+  # == URIs
   #
-  #   Net::HTTP.get('example.com', '/index.html') # => String
+  # On the internet, a URI
+  # ({Universal Resource Identifier}[https://en.wikipedia.org/wiki/Uniform_Resource_Identifier])
+  # is a string that identifies a particular resource.
+  # It consists of some or all of: scheme, hostname, path, query, and fragment;
+  # see {URI syntax}[https://en.wikipedia.org/wiki/Uniform_Resource_Identifier#Syntax].
   #
-  # === GET by URI
+  # A Ruby {URI::Generic}[rdoc-ref:URI::Generic] object
+  # represents an internet URI.
+  # It provides, among others, methods
+  # +scheme+, +hostname+, +path+, +query+, and +fragment+.
   #
-  #   uri = URI('http://example.com/index.html?count=10')
-  #   Net::HTTP.get(uri) # => String
+  # === Schemes
   #
-  # === GET with Dynamic Parameters
+  # An internet \URI has
+  # a {scheme}[https://en.wikipedia.org/wiki/List_of_URI_schemes].
   #
-  #   uri = URI('http://example.com/index.html')
-  #   params = { :limit => 10, :page => 3 }
-  #   uri.query = URI.encode_www_form(params)
+  # The two schemes supported in \Net::HTTP are <tt>'https'</tt> and <tt>'http'</tt>:
   #
-  #   res = Net::HTTP.get_response(uri)
-  #   puts res.body if res.is_a?(Net::HTTPSuccess)
+  #   uri.scheme                       # => "https"
+  #   URI('http://example.com').scheme # => "http"
   #
-  # === POST
+  # === Hostnames
   #
-  #   uri = URI('http://www.example.com/search.cgi')
-  #   res = Net::HTTP.post_form(uri, 'q' => 'ruby', 'max' => '50')
-  #   puts res.body
+  # A hostname identifies a server (host) to which requests may be sent:
   #
-  # === POST with Multiple Values
+  #   hostname = uri.hostname # => "jsonplaceholder.typicode.com"
+  #   Net::HTTP.start(hostname) do |http|
+  #     # Some HTTP stuff.
+  #   end
   #
-  #   uri = URI('http://www.example.com/search.cgi')
-  #   res = Net::HTTP.post_form(uri, 'q' => ['ruby', 'perl'], 'max' => '50')
-  #   puts res.body
+  # === Paths
   #
-  # == How to use Net::HTTP
+  # A host-specific path identifies a resource on the host:
   #
-  # The following example code can be used as the basis of an HTTP user-agent
-  # which can perform a variety of request types using persistent
-  # connections.
+  #   _uri = uri.dup
+  #   _uri.path = '/todos/1'
+  #   hostname = _uri.hostname
+  #   path = _uri.path
+  #   Net::HTTP.get(hostname, path)
   #
-  #   uri = URI('http://example.com/some_path?query=string')
+  # === Queries
   #
-  #   Net::HTTP.start(uri.host, uri.port) do |http|
-  #     request = Net::HTTP::Get.new uri
+  # A host-specific query adds name/value pairs to the URI:
   #
-  #     response = http.request request # Net::HTTPResponse object
-  #   end
+  #   _uri = uri.dup
+  #   params = {userId: 1, completed: false}
+  #   _uri.query = URI.encode_www_form(params)
+  #   _uri # => #<URI::HTTPS https://jsonplaceholder.typicode.com?userId=1&completed=false>
+  #   Net::HTTP.get(_uri)
   #
-  # Net::HTTP::start immediately creates a connection to an HTTP server which
-  # is kept open for the duration of the block.  The connection will remain
-  # open for multiple requests in the block if the server indicates it
-  # supports persistent connections.
+  # === Fragments
   #
-  # If you wish to re-use a connection across multiple HTTP requests without
-  # automatically closing it you can use ::new and then call #start and
-  # #finish manually.
+  # A {URI fragment}[https://en.wikipedia.org/wiki/URI_fragment] has no effect
+  # in \Net::HTTP;
+  # the same data is returned, regardless of whether a fragment is included.
   #
-  # The request types Net::HTTP supports are listed below in the section "HTTP
-  # Request Classes".
+  # == Request Headers
   #
-  # For all the Net::HTTP request objects and shortcut request methods you may
-  # supply either a String for the request path or a URI from which Net::HTTP
-  # will extract the request path.
+  # Request headers may be used to pass additional information to the host,
+  # similar to arguments passed in a method call;
+  # each header is a name/value pair.
   #
-  # === Response Data
+  # Each of the \Net::HTTP methods that sends a request to the host
+  # has optional argument +headers+,
+  # where the headers are expressed as a hash of field-name/value pairs:
   #
-  #   uri = URI('http://example.com/index.html')
-  #   res = Net::HTTP.get_response(uri)
+  #   headers = {Accept: 'application/json', Connection: 'Keep-Alive'}
+  #   Net::HTTP.get(uri, headers)
   #
-  #   # Headers
-  #   res['Set-Cookie']            # => String
-  #   res.get_fields('set-cookie') # => Array
-  #   res.to_hash['set-cookie']    # => Array
-  #   puts "Headers: #{res.to_hash.inspect}"
+  # See lists of both standard request fields and common request fields at
+  # {Request Fields}[https://en.wikipedia.org/wiki/List_of_HTTP_header_fields#Request_fields].
+  # A host may also accept other custom fields.
   #
-  #   # Status
-  #   puts res.code       # => '200'
-  #   puts res.message    # => 'OK'
-  #   puts res.class.name # => 'HTTPOK'
+  # == Sessions
   #
-  #   # Body
-  #   puts res.body
+  # A _session_ is a connection between a server (host) and a client that:
+  #
+  # - Is begun by instance method Net::HTTP#start.
+  # - May contain any number of requests.
+  # - Is ended by instance method Net::HTTP#finish.
+  #
+  # See example sessions at the {Synopsis}[rdoc-ref:Net::HTTP@Synopsis].
+  #
+  # === Session Using \Net::HTTP.start
+  #
+  # If you have many requests to make to a single host (and port),
+  # consider using singleton method Net::HTTP.start with a block;
+  # the method handles the session automatically by:
+  #
+  # - Calling #start before block execution.
+  # - Executing the block.
+  # - Calling #finish after block execution.
+  #
+  # In the block, you can use these instance methods,
+  # each of which that sends a single request:
+  #
+  # - {HTTP methods}[https://en.wikipedia.org/wiki/Hypertext_Transfer_Protocol#Request_methods]:
+  #
+  #   - #get, #request_get: GET.
+  #   - #head, #request_head: HEAD.
+  #   - #post, #request_post: POST.
+  #   - #delete: DELETE.
+  #   - #options: OPTIONS.
+  #   - #trace: TRACE.
+  #   - #patch: PATCH.
+  #
+  # - {WebDAV methods}[https://en.wikipedia.org/wiki/WebDAV#Implementation]:
+  #
+  #   - #copy: COPY.
+  #   - #lock: LOCK.
+  #   - #mkcol: MKCOL.
+  #   - #move: MOVE.
+  #   - #propfind: PROPFIND.
+  #   - #proppatch: PROPPATCH.
+  #   - #unlock: UNLOCK.
   #
-  # === Following Redirection
+  # === Session Using \Net::HTTP.start and \Net::HTTP.finish
+  #
+  # You can manage a session manually using methods #start and #finish:
+  #
+  #   http = Net::HTTP.new(hostname)
+  #   http.start
+  #   http.get('/todos/1')
+  #   http.get('/todos/2')
+  #   http.delete('/posts/1')
+  #   http.finish # Needed to free resources.
+  #
+  # === Single-Request Session
+  #
+  # Certain convenience methods automatically handle a session by:
+  #
+  # - Creating an \HTTP object
+  # - Starting a session.
+  # - Sending a single request.
+  # - Finishing the session.
+  # - Destroying the object.
+  #
+  # Such methods that send GET requests:
+  #
+  # - ::get: Returns the string response body.
+  # - ::get_print: Writes the string response body to $stdout.
+  # - ::get_response: Returns a Net::HTTPResponse object.
+  #
+  # Such methods that send POST requests:
+  #
+  # - ::post: Posts data to the host.
+  # - ::post_form: Posts form data to the host.
+  #
+  # == \HTTP Requests and Responses
+  #
+  # Many of the methods above are convenience methods,
+  # each of which sends a request and returns a string
+  # without directly using \Net::HTTPRequest and \Net::HTTPResponse objects.
+  #
+  # You can, however, directly create a request object, send the request,
+  # and retrieve the response object; see:
+  #
+  # - Net::HTTPRequest.
+  # - Net::HTTPResponse.
+  #
+  # == Following Redirection
   #
   # Each Net::HTTPResponse object belongs to a class for its response code.
   #
@@ -167,56 +294,7 @@ class HTTPHeaderSyntaxError < StandardError; end
   #
   #   print fetch('http://www.ruby-lang.org')
   #
-  # === POST
-  #
-  # A POST can be made using the Net::HTTP::Post request class.  This example
-  # creates a URL encoded POST body:
-  #
-  #   uri = URI('http://www.example.com/todo.cgi')
-  #   req = Net::HTTP::Post.new(uri)
-  #   req.set_form_data('from' => '2005-01-01', 'to' => '2005-03-31')
-  #
-  #   res = Net::HTTP.start(uri.hostname, uri.port) do |http|
-  #     http.request(req)
-  #   end
-  #
-  #   case res
-  #   when Net::HTTPSuccess, Net::HTTPRedirection
-  #     # OK
-  #   else
-  #     res.value
-  #   end
-  #
-  # To send multipart/form-data use Net::HTTPHeader#set_form:
-  #
-  #   req = Net::HTTP::Post.new(uri)
-  #   req.set_form([['upload', File.open('foo.bar')]], 'multipart/form-data')
-  #
-  # Other requests that can contain a body such as PUT can be created in the
-  # same way using the corresponding request class (Net::HTTP::Put).
-  #
-  # === Setting Headers
-  #
-  # The following example performs a conditional GET using the
-  # If-Modified-Since header.  If the files has not been modified since the
-  # time in the header a Not Modified response will be returned.  See RFC 2616
-  # section 9.3 for further details.
-  #
-  #   uri = URI('http://example.com/cached_response')
-  #   file = File.stat 'cached_response'
-  #
-  #   req = Net::HTTP::Get.new(uri)
-  #   req['If-Modified-Since'] = file.mtime.rfc2822
-  #
-  #   res = Net::HTTP.start(uri.hostname, uri.port) {|http|
-  #     http.request(req)
-  #   }
-  #
-  #   open 'cached_response', 'w' do |io|
-  #     io.write res.body
-  #   end if res.is_a?(Net::HTTPSuccess)
-  #
-  # === Basic Authentication
+  # == Basic Authentication
   #
   # Basic authentication is performed according to
   # [RFC2617](http://www.ietf.org/rfc/rfc2617.txt).
@@ -231,7 +309,7 @@ class HTTPHeaderSyntaxError < StandardError; end
   #   }
   #   puts res.body
   #
-  # === Streaming Response Bodies
+  # == Streaming Response Bodies
   #
   # By default Net::HTTP reads an entire response into memory.  If you are
   # handling large files or wish to implement a progress bar you can instead
@@ -251,7 +329,7 @@ class HTTPHeaderSyntaxError < StandardError; end
   #     end
   #   end
   #
-  # === HTTPS
+  # == HTTPS
   #
   # HTTPS is enabled for an HTTP connection by Net::HTTP#use_ssl=.
   #
@@ -272,7 +350,7 @@ class HTTPHeaderSyntaxError < StandardError; end
   # In previous versions of Ruby you would need to require 'net/https' to use
   # HTTPS. This is no longer true.
   #
-  # === Proxies
+  # == Proxies
   #
   # Net::HTTP will automatically create a proxy from the +http_proxy+
   # environment variable if it is present.  To disable use of +http_proxy+,
@@ -290,7 +368,7 @@ class HTTPHeaderSyntaxError < StandardError; end
   # See Net::HTTP.new for further details and examples such as proxies that
   # require a username and password.
   #
-  # === Compression
+  # == Compression
   #
   # Net::HTTP automatically adds Accept-Encoding for compression of response
   # bodies and automatically decompresses gzip and deflate responses unless a
@@ -298,114 +376,6 @@ class HTTPHeaderSyntaxError < StandardError; end
   #
   # Compression can be disabled through the Accept-Encoding: identity header.
   #
-  # == \HTTP Request Classes
-  #
-  # Here is the hierarchy of \HTTP request classes
-  #
-  # - Net::HTTPRequest
-  #
-  #   - Net::HTTP::Get
-  #   - Net::HTTP::Head
-  #   - Net::HTTP::Post
-  #   - Net::HTTP::Patch
-  #   - Net::HTTP::Put
-  #   - Net::HTTP::Proppatch
-  #   - Net::HTTP::Lock
-  #   - Net::HTTP::Unlock
-  #   - Net::HTTP::Options
-  #   - Net::HTTP::Propfind
-  #   - Net::HTTP::Delete
-  #   - Net::HTTP::Move
-  #   - Net::HTTP::Copy
-  #   - Net::HTTP::Mkcol
-  #   - Net::HTTP::Trace
-  #
-  # == \HTTP Response Classes
-  #
-  # Here is the \HTTP response class hierarchy (with status codes):
-  #
-  # - Net::HTTPResponse:
-  #
-  #   - Net::HTTPUnknownResponse (for unhandled \HTTP extensions).
-  #
-  #   - Net::HTTPInformation:
-  #
-  #     - Net::HTTPContinue (100)
-  #     - Net::HTTPSwitchProtocol (101)
-  #     - Net::HTTPProcessing (102)
-  #     - Net::HTTPEarlyHints (103)
-  #
-  #   - Net::HTTPSuccess:
-  #
-  #     - Net::HTTPOK (200)
-  #     - Net::HTTPCreated (201)
-  #     - Net::HTTPAccepted (202)
-  #     - Net::HTTPNonAuthoritativeInformation (203)
-  #     - Net::HTTPNoContent (204)
-  #     - Net::HTTPResetContent (205)
-  #     - Net::HTTPPartialContent (206)
-  #     - Net::HTTPMultiStatus (207)
-  #     - Net::HTTPAlreadyReported (208)
-  #     - Net::HTTPIMUsed (226)
-  #
-  #   - Net::HTTPRedirection:
-  #
-  #     - Net::HTTPMultipleChoices (300)
-  #     - Net::HTTPMovedPermanently (301)
-  #     - Net::HTTPFound (302)
-  #     - Net::HTTPSeeOther (303)
-  #     - Net::HTTPNotModified (304)
-  #     - Net::HTTPUseProxy (305)
-  #     - Net::HTTPTemporaryRedirect (307)
-  #     - Net::HTTPPermanentRedirect (308)
-  #
-  #   - Net::HTTPClientError:
-  #
-  #     - Net::HTTPBadRequest (400)
-  #     - Net::HTTPUnauthorized (401)
-  #     - Net::HTTPPaymentRequired (402)
-  #     - Net::HTTPForbidden (403)
-  #     - Net::HTTPNotFound (404)
-  #     - Net::HTTPMethodNotAllowed (405)
-  #     - Net::HTTPNotAcceptable (406)
-  #     - Net::HTTPProxyAuthenticationRequired (407)
-  #     - Net::HTTPRequestTimeOut (408)
-  #     - Net::HTTPConflict (409)
-  #     - Net::HTTPGone (410)
-  #     - Net::HTTPLengthRequired (411)
-  #     - Net::HTTPPreconditionFailed (412)
-  #     - Net::HTTPRequestEntityTooLarge (413)
-  #     - Net::HTTPRequestURITooLong (414)
-  #     - Net::HTTPUnsupportedMediaType (415)
-  #     - Net::HTTPRequestedRangeNotSatisfiable (416)
-  #     - Net::HTTPExpectationFailed (417)
-  #     - Net::HTTPMisdirectedRequest (421)
-  #     - Net::HTTPUnprocessableEntity (422)
-  #     - Net::HTTPLocked (423)
-  #     - Net::HTTPFailedDependency (424)
-  #     - Net::HTTPUpgradeRequired (426)
-  #     - Net::HTTPPreconditionRequired (428)
-  #     - Net::HTTPTooManyRequests (429)
-  #     - Net::HTTPRequestHeaderFieldsTooLarge (431)
-  #     - Net::HTTPUnavailableForLegalReasons (451)
-  #
-  #   - Net::HTTPServerError:
-  #
-  #     - Net::HTTPInternalServerError (500)
-  #     - Net::HTTPNotImplemented (501)
-  #     - Net::HTTPBadGateway (502)
-  #     - Net::HTTPServiceUnavailable (503)
-  #     - Net::HTTPGatewayTimeOut (504)
-  #     - Net::HTTPVersionNotSupported (505)
-  #     - Net::HTTPVariantAlsoNegotiates (506)
-  #     - Net::HTTPInsufficientStorage (507)
-  #     - Net::HTTPLoopDetected (508)
-  #     - Net::HTTPNotExtended (510)
-  #     - Net::HTTPNetworkAuthenticationRequired (511)
-  #
-  # There is also the Net::HTTPBadResponse exception which is raised when
-  # there is a protocol error.
-  #
   class HTTP < Protocol
 
     # :stopdoc:
@@ -420,18 +390,17 @@ class HTTP < Protocol
     end
     # :startdoc:
 
-    # Turns on net/http 1.2 (Ruby 1.8) features.
-    # Defaults to ON in Ruby 1.8 or later.
+    # Returns +true+; retained for compatibility.
     def HTTP.version_1_2
       true
     end
 
-    # Returns true if net/http is in version 1.2 mode.
-    # Defaults to true.
+    # Returns +true+; retained for compatibility.
     def HTTP.version_1_2?
       true
     end
 
+    # Returns +false+; retained for compatibility.
     def HTTP.version_1_1?  #:nodoc:
       false
     end
@@ -441,25 +410,12 @@ class << HTTP
       alias is_version_1_2? version_1_2?   #:nodoc:
     end
 
+    # :call-seq:
+    #   Net::HTTP.get_print(hostname, path, port = 80) -> nil
+    #   Net::HTTP:get_print(uri, headers = {}, port = uri.port) -> nil
     #
-    # short cut methods
-    #
-
-    #
-    # Gets the body text from the target and outputs it to $stdout.  The
-    # target can either be specified as
-    # (+uri+, +headers+), or as (+host+, +path+, +port+ = 80); so:
-    #
-    #    Net::HTTP.get_print URI('http://www.example.com/index.html')
-    #
-    # or:
-    #
-    #    Net::HTTP.get_print 'www.example.com', '/index.html'
-    #
-    # you can also specify request headers:
-    #
-    #    Net::HTTP.get_print URI('http://www.example.com/index.html'), { 'Accept' => 'text/html' }
-    #
+    # Like Net::HTTP.get, but writes the returned body to $stdout;
+    # returns +nil+.
     def HTTP.get_print(uri_or_host, path_or_headers = nil, port = nil)
       get_response(uri_or_host, path_or_headers, port) {|res|
         res.read_body do |chunk|
@@ -469,40 +425,43 @@ def HTTP.get_print(uri_or_host, path_or_headers = nil, port = nil)
       nil
     end
 
-    # Sends a GET request to the target and returns the HTTP response
-    # as a string.  The target can either be specified as
-    # (+uri+, +headers+), or as (+host+, +path+, +port+ = 80); so:
+    # :call-seq:
+    #   Net::HTTP.get(hostname, path, port = 80) -> body
+    #   Net::HTTP:get(uri, headers = {}, port = uri.port) -> body
     #
-    #    print Net::HTTP.get(URI('http://www.example.com/index.html'))
+    # Sends a GET request and returns the \HTTP response body as a string.
     #
-    # or:
+    # With string arguments +hostname+ and +path+:
     #
-    #    print Net::HTTP.get('www.example.com', '/index.html')
+    #   hostname = 'jsonplaceholder.typicode.com'
+    #   path = '/todos/1'
+    #   puts Net::HTTP.get(hostname, path)
     #
-    # you can also specify request headers:
+    # Output:
     #
-    #    Net::HTTP.get(URI('http://www.example.com/index.html'), { 'Accept' => 'text/html' })
+    #   {
+    #     "userId": 1,
+    #     "id": 1,
+    #     "title": "delectus aut autem",
+    #     "completed": false
+    #   }
+    #
+    # With URI object +uri+ and optional hash argument +headers+:
+    #
+    #   uri = URI('https://jsonplaceholder.typicode.com/todos/1')
+    #   headers = {'Content-type' => 'application/json; charset=UTF-8'}
+    #   Net::HTTP.get(uri, headers)
     #
     def HTTP.get(uri_or_host, path_or_headers = nil, port = nil)
       get_response(uri_or_host, path_or_headers, port).body
     end
 
-    # Sends a GET request to the target and returns the HTTP response
-    # as a Net::HTTPResponse object.  The target can either be specified as
-    # (+uri+, +headers+), or as (+host+, +path+, +port+ = 80); so:
-    #
-    #    res = Net::HTTP.get_response(URI('http://www.example.com/index.html'))
-    #    print res.body
-    #
-    # or:
-    #
-    #    res = Net::HTTP.get_response('www.example.com', '/index.html')
-    #    print res.body
-    #
-    # you can also specify request headers:
-    #
-    #    Net::HTTP.get_response(URI('http://www.example.com/index.html'), { 'Accept' => 'text/html' })
+    # :call-seq:
+    #   Net::HTTP.get_response(hostname, path, port = 80) -> http_response
+    #   Net::HTTP:get_response(uri, headers = {}, port = uri.port) -> http_response
     #
+    # Like Net::HTTP.get, but returns an Net::HTTPResponse object
+    # instead of the body string.
     def HTTP.get_response(uri_or_host, path_or_headers = nil, port = nil, &block)
       if path_or_headers && !path_or_headers.is_a?(Hash)
         host = uri_or_host
@@ -589,35 +548,80 @@ def HTTP.socket_type   #:nodoc: obsolete
     end
 
     # :call-seq:
-    #   HTTP.start(address, port, p_addr, p_port, p_user, p_pass, &block)
-    #   HTTP.start(address, port=nil, p_addr=:ENV, p_port=nil, p_user=nil, p_pass=nil, opt, &block)
-    #
-    # Creates a new Net::HTTP object, then additionally opens the TCP
-    # connection and HTTP session.
-    #
-    # Arguments are the following:
-    # _address_ :: hostname or IP address of the server
-    # _port_    :: port of the server
-    # _p_addr_  :: address of proxy
-    # _p_port_  :: port of proxy
-    # _p_user_  :: user of proxy
-    # _p_pass_  :: pass of proxy
-    # _opt_     :: optional hash
-    #
-    # _opt_ sets following values by its accessor.
-    # The keys are ipaddr, ca_file, ca_path, cert, cert_store, ciphers, keep_alive_timeout,
-    # close_on_empty_response, key, open_timeout, read_timeout, write_timeout, ssl_timeout,
-    # ssl_version, use_ssl, verify_callback, verify_depth and verify_mode.
-    # If you set :use_ssl as true, you can use https and default value of
-    # verify_mode is set as OpenSSL::SSL::VERIFY_PEER.
-    #
-    # If the optional block is given, the newly
-    # created Net::HTTP object is passed to it and closed when the
-    # block finishes.  In this case, the return value of this method
-    # is the return value of the block.  If no block is given, the
-    # return value of this method is the newly created Net::HTTP object
-    # itself, and the caller is responsible for closing it upon completion
-    # using the finish() method.
+    #   HTTP.start(address, port, p_addr, p_port, p_user, p_pass) {|http| ... }
+    #   HTTP.start(address, port=nil, p_addr=:ENV, p_port=nil, p_user=nil, p_pass=nil, opt) {|http| ... }
+    # Creates a new \Net::HTTP object,
+    # opens a TCP connection and \HTTP session.
+    #
+    # Argument +address+ is the hostname or IP address of the server.
+    #
+    # With a block given:
+    #
+    # - Passes the object to the given block,
+    #   which may make any number of requests to the host.
+    # - Closes the \HTTP session on block exit.
+    # - Returns the block's value.
+    #
+    # Example:
+    #
+    #   hostname = 'jsonplaceholder.typicode.com'
+    #   Net::HTTP.start(hostname) do |http|
+    #     puts http.get('/todos/1').body
+    #     puts http.get('/todos/2').body
+    #   end
+    #
+    # Output:
+    #
+    #   {
+    #     "userId": 1,
+    #     "id": 1,
+    #     "title": "delectus aut autem",
+    #     "completed": false
+    #   }
+    #   {
+    #     "userId": 1,
+    #     "id": 2,
+    #     "title": "quis ut nam facilis et officia qui",
+    #     "completed": false
+    #   }
+    #
+    # With no block given, returns the \Net::HTTP object;
+    # the caller should call #finish to close the session.
+    #
+    # Other arguments:
+    #
+    # - +port+: Server port number.
+    # - +p_addr+: Proxy address.
+    # - +p_port+: Proxy port.
+    # - +p_user+: Proxy user name.
+    # - +p_pass+: Proxy password.
+    # - +opts+: Optional options hash.
+    #
+    # The options hash +opts+ sets certain values,
+    # where each key is a method or accessor to be called,
+    # and its value is the value to be set.
+    #
+    # The keys may include:
+    #
+    # - #ca_file
+    # - #ca_path
+    # - #cert
+    # - #cert_store
+    # - #ciphers
+    # - #close_on_empty_response
+    # - +ipaddr+ (calls #ipaddr=)
+    # - #keep_alive_timeout
+    # - #key
+    # - #open_timeout
+    # - #read_timeout
+    # - #ssl_timeout
+    # - #ssl_version
+    # - +use_ssl+ (calls #use_ssl=)
+    # - #verify_callback
+    # - #verify_depth
+    # - #verify_mode
+    # - #write_timeout
+    #
     def HTTP.start(address, *arg, &block) # :yield: +http+
       arg.pop if opt = Hash.try_convert(arg[-1])
       port, p_addr, p_port, p_user, p_pass = *arg
diff --git a/lib/net/http/request.rb b/lib/net/http/request.rb
index 1e86f3e4b47365..279316e0b9e332 100644
--- a/lib/net/http/request.rb
+++ b/lib/net/http/request.rb
@@ -1,8 +1,26 @@
 # frozen_string_literal: false
-# HTTP request class.
-# This class wraps together the request header and the request path.
-# You cannot use this class directly. Instead, you should use one of its
-# subclasses: Net::HTTP::Get, Net::HTTP::Post, Net::HTTP::Head.
+
+# This class is the base class for \Net::HTTP request classes;
+# it wraps together the request path and the request headers.
+#
+# The class should not be used directly;
+# instead you should use its subclasses:
+#
+# - \Net::HTTP::Get
+# - \Net::HTTP::Head
+# - \Net::HTTP::Post
+# - \Net::HTTP::Delete
+# - \Net::HTTP::Options
+# - \Net::HTTP::Trace
+# - \Net::HTTP::Patch
+# - \Net::HTTP::Put
+# - \Net::HTTP::Copy
+# - \Net::HTTP::Lock
+# - \Net::HTTP::Mkcol
+# - \Net::HTTP::Move
+# - \Net::HTTP::Propfind
+# - \Net::HTTP::Proppatch
+# - \Net::HTTP::Unlock
 #
 class Net::HTTPRequest < Net::HTTPGenericRequest
   # Creates an HTTP request object for +path+.
diff --git a/lib/net/http/response.rb b/lib/net/http/response.rb
index f8b522f1ff596d..83853ffd1942de 100644
--- a/lib/net/http/response.rb
+++ b/lib/net/http/response.rb
@@ -1,20 +1,136 @@
 # frozen_string_literal: false
-# HTTP response class.
+
+# This class is the base class for \Net::HTTP request classes.
+#
+# == About the Examples
+#
+# :include: doc/net-http/examples.rdoc
+#
+# == Returned Responses
+#
+# \Method Net::HTTP.get_response returns
+# an instance of one of the subclasses of \Net::HTTPResponse:
+#
+#   Net::HTTP.get_response(uri)
+#   # => #<Net::HTTPOK 200 OK readbody=true>
+#   Net::HTTP.get_response(hostname, '/nosuch')
+#   # => #<Net::HTTPNotFound 404 Not Found readbody=true>
+#
+# As does method Net::HTTP#request:
+#
+#   req = Net::HTTP::Get.new(uri)
+#   Net::HTTP.start(hostname) do |http|
+#     http.request(req)
+#   end # => #<Net::HTTPOK 200 OK readbody=true>
+#
+# \Class \Net::HTTPResponse includes module Net::HTTPHeader,
+# which provides access to response header values via (among others):
+#
+# - \Hash-like method <tt>[]</tt>.
+# - Specific reader methods, such as +content_type+.
+#
+# Examples:
+#
+#   res = Net::HTTP.get_response(uri) # => #<Net::HTTPOK 200 OK readbody=true>
+#   res['Content-Type']               # => "text/html; charset=UTF-8"
+#   res.content_type                  # => "text/html"
+#
+# == Response Subclasses
+#
+# \Class \Net::HTTPResponse has a subclass for each
+# {HTTP status code}[https://en.wikipedia.org/wiki/List_of_HTTP_status_codes].
+# You can look up the response class for a given code:
+#
+#   Net::HTTPResponse::CODE_TO_OBJ['200'] # => Net::HTTPOK
+#   Net::HTTPResponse::CODE_TO_OBJ['400'] # => Net::HTTPBadRequest
+#   Net::HTTPResponse::CODE_TO_OBJ['404'] # => Net::HTTPNotFound
+#
+# And you can retrieve the status code for a response object:
+#
+#   Net::HTTP.get_response(uri).code                 # => "200"
+#   Net::HTTP.get_response(hostname, '/nosuch').code # => "404"
+#
+# The response subclasses (indentation shows class hierarchy):
+#
+# - Net::HTTPUnknownResponse (for unhandled \HTTP extensions).
+#
+# - Net::HTTPInformation:
+#
+#   - Net::HTTPContinue (100)
+#   - Net::HTTPSwitchProtocol (101)
+#   - Net::HTTPProcessing (102)
+#   - Net::HTTPEarlyHints (103)
+#
+# - Net::HTTPSuccess:
+#
+#   - Net::HTTPOK (200)
+#   - Net::HTTPCreated (201)
+#   - Net::HTTPAccepted (202)
+#   - Net::HTTPNonAuthoritativeInformation (203)
+#   - Net::HTTPNoContent (204)
+#   - Net::HTTPResetContent (205)
+#   - Net::HTTPPartialContent (206)
+#   - Net::HTTPMultiStatus (207)
+#   - Net::HTTPAlreadyReported (208)
+#   - Net::HTTPIMUsed (226)
+#
+# - Net::HTTPRedirection:
+#
+#   - Net::HTTPMultipleChoices (300)
+#   - Net::HTTPMovedPermanently (301)
+#   - Net::HTTPFound (302)
+#   - Net::HTTPSeeOther (303)
+#   - Net::HTTPNotModified (304)
+#   - Net::HTTPUseProxy (305)
+#   - Net::HTTPTemporaryRedirect (307)
+#   - Net::HTTPPermanentRedirect (308)
 #
-# This class wraps together the response header and the response body (the
-# entity requested).
+# - Net::HTTPClientError:
 #
-# It mixes in the HTTPHeader module, which provides access to response
-# header values both via hash-like methods and via individual readers.
+#   - Net::HTTPBadRequest (400)
+#   - Net::HTTPUnauthorized (401)
+#   - Net::HTTPPaymentRequired (402)
+#   - Net::HTTPForbidden (403)
+#   - Net::HTTPNotFound (404)
+#   - Net::HTTPMethodNotAllowed (405)
+#   - Net::HTTPNotAcceptable (406)
+#   - Net::HTTPProxyAuthenticationRequired (407)
+#   - Net::HTTPRequestTimeOut (408)
+#   - Net::HTTPConflict (409)
+#   - Net::HTTPGone (410)
+#   - Net::HTTPLengthRequired (411)
+#   - Net::HTTPPreconditionFailed (412)
+#   - Net::HTTPRequestEntityTooLarge (413)
+#   - Net::HTTPRequestURITooLong (414)
+#   - Net::HTTPUnsupportedMediaType (415)
+#   - Net::HTTPRequestedRangeNotSatisfiable (416)
+#   - Net::HTTPExpectationFailed (417)
+#   - Net::HTTPMisdirectedRequest (421)
+#   - Net::HTTPUnprocessableEntity (422)
+#   - Net::HTTPLocked (423)
+#   - Net::HTTPFailedDependency (424)
+#   - Net::HTTPUpgradeRequired (426)
+#   - Net::HTTPPreconditionRequired (428)
+#   - Net::HTTPTooManyRequests (429)
+#   - Net::HTTPRequestHeaderFieldsTooLarge (431)
+#   - Net::HTTPUnavailableForLegalReasons (451)
 #
-# Note that each possible HTTP response code defines its own
-# HTTPResponse subclass. All classes are defined under the Net module.
-# Indentation indicates inheritance.  For a list of the classes see Net::HTTP.
+# - Net::HTTPServerError:
 #
-# Correspondence <code>HTTP code => class</code> is stored in CODE_TO_OBJ
-# constant:
+#   - Net::HTTPInternalServerError (500)
+#   - Net::HTTPNotImplemented (501)
+#   - Net::HTTPBadGateway (502)
+#   - Net::HTTPServiceUnavailable (503)
+#   - Net::HTTPGatewayTimeOut (504)
+#   - Net::HTTPVersionNotSupported (505)
+#   - Net::HTTPVariantAlsoNegotiates (506)
+#   - Net::HTTPInsufficientStorage (507)
+#   - Net::HTTPLoopDetected (508)
+#   - Net::HTTPNotExtended (510)
+#   - Net::HTTPNetworkAuthenticationRequired (511)
 #
-#    Net::HTTPResponse::CODE_TO_OBJ['404'] #=> Net::HTTPNotFound
+# There is also the Net::HTTPBadResponse exception which is raised when
+# there is a protocol error.
 #
 class Net::HTTPResponse
   class << self
diff --git a/lib/racc/racc.gemspec b/lib/racc/racc.gemspec
index 7ee706f63d7139..1095c8f47e0383 100644
--- a/lib/racc/racc.gemspec
+++ b/lib/racc/racc.gemspec
@@ -20,7 +20,7 @@ Racc is a LALR(1) parser generator.
 DESC
   s.authors = ["Minero Aoki", "Aaron Patterson"]
   s.email = [nil, "aaron@tenderlovemaking.com"]
-  s.homepage = "https://i.loveruby.net/en/projects/racc/"
+  s.homepage = "https://github.com/ruby/racc"
   s.licenses = ["Ruby", "BSD-2-Clause"]
   s.executables = ["racc"]
   s.files = [
diff --git a/load.c b/load.c
index 0e75c1ab838fc7..5900a6af8e0b10 100644
--- a/load.c
+++ b/load.c
@@ -1028,13 +1028,13 @@ search_required(rb_vm_t *vm, VALUE fname, volatile VALUE *path, feature_func rb_
     switch (type) {
       case 0:
         if (ft)
-            goto statically_linked;
+            goto feature_present;
         ftptr = RSTRING_PTR(tmp);
         return rb_feature_p(vm, ftptr, 0, FALSE, TRUE, 0);
 
       default:
         if (ft) {
-            goto statically_linked;
+            goto feature_present;
         }
         /* fall through */
       case 1:
@@ -1045,7 +1045,7 @@ search_required(rb_vm_t *vm, VALUE fname, volatile VALUE *path, feature_func rb_
     }
     return type ? 's' : 'r';
 
-  statically_linked:
+  feature_present:
     if (loading) *path = rb_filesystem_str_new_cstr(loading);
     return ft;
 }
diff --git a/marshal.c b/marshal.c
index d956260d96f0a3..e1612303fe6bd4 100644
--- a/marshal.c
+++ b/marshal.c
@@ -743,7 +743,7 @@ w_ivar(st_index_t num, VALUE ivobj, VALUE encname, struct dump_call_arg *arg)
         w_object(Qtrue, arg->arg, limit);
         num--;
     }
-    if (ivobj != Qundef && num) {
+    if (!UNDEF_P(ivobj) && num) {
         w_ivar_each(ivobj, num, arg);
     }
 }
@@ -930,7 +930,7 @@ w_object(VALUE obj, struct dump_arg *arg, int limit)
                     arg->compat_tbl = rb_init_identtable();
                 }
                 st_insert(arg->compat_tbl, (st_data_t)obj, (st_data_t)real_obj);
-                if (obj != real_obj && ivobj == Qundef) hasiv = 0;
+                if (obj != real_obj && UNDEF_P(ivobj)) hasiv = 0;
             }
         }
         if (hasiv) w_byte(TYPE_IVAR, arg);
@@ -2251,7 +2251,7 @@ r_object_for(struct load_arg *arg, bool partial, int *ivp, VALUE extmod, int typ
         break;
     }
 
-    if (v == Qundef) {
+    if (UNDEF_P(v)) {
         rb_raise(rb_eArgError, "dump format error (bad link)");
     }
 
diff --git a/mjit.c b/mjit.c
index d1a9e71f4f1a7e..824287e3290abe 100644
--- a/mjit.c
+++ b/mjit.c
@@ -1628,7 +1628,7 @@ system_tmpdir(void)
 // Default permitted number of units with a JIT code kept in memory.
 #define DEFAULT_MAX_CACHE_SIZE 10000
 // A default threshold used to add iseq to JIT.
-#define DEFAULT_MIN_CALLS_TO_ADD 10000
+#define DEFAULT_CALL_THRESHOLD 10000
 
 // Start MJIT worker. Return TRUE if worker is successfully started.
 static bool
@@ -1709,8 +1709,8 @@ mjit_setup_options(const char *s, struct mjit_options *mjit_opt)
     else if (opt_match_arg(s, l, "max-cache")) {
         mjit_opt->max_cache_size = atoi(s + 1);
     }
-    else if (opt_match_arg(s, l, "min-calls")) {
-        mjit_opt->min_calls = atoi(s + 1);
+    else if (opt_match_arg(s, l, "call-threshold")) {
+        mjit_opt->call_threshold = atoi(s + 1);
     }
     // --mjit=pause is an undocumented feature for experiments
     else if (opt_match_noarg(s, l, "pause")) {
@@ -1724,15 +1724,15 @@ mjit_setup_options(const char *s, struct mjit_options *mjit_opt)
 
 #define M(shortopt, longopt, desc) RUBY_OPT_MESSAGE(shortopt, longopt, desc)
 const struct ruby_opt_message mjit_option_messages[] = {
-    M("--mjit-warnings",      "", "Enable printing JIT warnings"),
-    M("--mjit-debug",         "", "Enable JIT debugging (very slow), or add cflags if specified"),
-    M("--mjit-wait",          "", "Wait until JIT compilation finishes every time (for testing)"),
-    M("--mjit-save-temps",    "", "Save JIT temporary files in $TMP or /tmp (for testing)"),
-    M("--mjit-verbose=num",   "", "Print JIT logs of level num or less to stderr (default: 0)"),
-    M("--mjit-max-cache=num", "", "Max number of methods to be JIT-ed in a cache (default: "
+    M("--mjit-warnings",           "", "Enable printing JIT warnings"),
+    M("--mjit-debug",              "", "Enable JIT debugging (very slow), or add cflags if specified"),
+    M("--mjit-wait",               "", "Wait until JIT compilation finishes every time (for testing)"),
+    M("--mjit-save-temps",         "", "Save JIT temporary files in $TMP or /tmp (for testing)"),
+    M("--mjit-verbose=num",        "", "Print JIT logs of level num or less to stderr (default: 0)"),
+    M("--mjit-max-cache=num",      "", "Max number of methods to be JIT-ed in a cache (default: "
       STRINGIZE(DEFAULT_MAX_CACHE_SIZE) ")"),
-    M("--mjit-min-calls=num", "", "Number of calls to trigger JIT (for testing, default: "
-      STRINGIZE(DEFAULT_MIN_CALLS_TO_ADD) ")"),
+    M("--mjit-call-threshold=num", "", "Number of calls to trigger JIT (for testing, default: "
+      STRINGIZE(DEFAULT_CALL_THRESHOLD) ")"),
     {0}
 };
 #undef M
@@ -1760,8 +1760,8 @@ mjit_init(const struct mjit_options *opts)
     mjit_pid = getpid();
 
     // Normalize options
-    if (mjit_opts.min_calls == 0)
-        mjit_opts.min_calls = DEFAULT_MIN_CALLS_TO_ADD;
+    if (mjit_opts.call_threshold == 0)
+        mjit_opts.call_threshold = DEFAULT_CALL_THRESHOLD;
     if (mjit_opts.max_cache_size <= 0)
         mjit_opts.max_cache_size = DEFAULT_MAX_CACHE_SIZE;
     if (mjit_opts.max_cache_size < MIN_CACHE_SIZE)
diff --git a/mjit.h b/mjit.h
index 7b5ca54c6fc259..536ac9fa916c8e 100644
--- a/mjit.h
+++ b/mjit.h
@@ -52,7 +52,7 @@ struct mjit_options {
     // If true, all ISeqs are synchronously compiled. For testing.
     bool wait;
     // Number of calls to trigger JIT compilation. For testing.
-    unsigned int min_calls;
+    unsigned int call_threshold;
     // Force printing info about MJIT work of level VERBOSE or
     // less. 0=silence, 1=medium, 2=verbose.
     int verbose;
diff --git a/mjit_c.rb b/mjit_c.rb
index 322a8f15cfa465..c240a5ec4b9ca8 100644
--- a/mjit_c.rb
+++ b/mjit_c.rb
@@ -7,10 +7,6 @@ module RubyVM::MJIT
   # This `class << C` section is for calling C functions. For importing variables
   # or macros as is, please consider using tool/mjit/bindgen.rb instead.
   class << C
-    def ROBJECT_EMBED_LEN_MAX
-      Primitive.cexpr! 'INT2NUM(RBIMPL_EMBED_LEN_MAX_OF(VALUE))'
-    end
-
     def cdhash_to_hash(cdhash_addr)
       Primitive.cdhash_to_hash(cdhash_addr)
     end
@@ -162,10 +158,6 @@ def C.VM_METHOD_TYPE_ISEQ
     Primitive.cexpr! %q{ INT2NUM(VM_METHOD_TYPE_ISEQ) }
   end
 
-  def C.SHAPE_BITS
-    Primitive.cexpr! %q{ UINT2NUM(SHAPE_BITS) }
-  end
-
   def C.SHAPE_CAPACITY_CHANGE
     Primitive.cexpr! %q{ UINT2NUM(SHAPE_CAPACITY_CHANGE) }
   end
@@ -178,6 +170,10 @@ def C.SHAPE_FROZEN
     Primitive.cexpr! %q{ UINT2NUM(SHAPE_FROZEN) }
   end
 
+  def C.SHAPE_ID_NUM_BITS
+    Primitive.cexpr! %q{ UINT2NUM(SHAPE_ID_NUM_BITS) }
+  end
+
   def C.SHAPE_INITIAL_CAPACITY
     Primitive.cexpr! %q{ UINT2NUM(SHAPE_INITIAL_CAPACITY) }
   end
@@ -330,7 +326,7 @@ def C.mjit_options
       debug: [self._Bool, Primitive.cexpr!("OFFSETOF((*((struct mjit_options *)NULL)), debug)")],
       debug_flags: [CType::Pointer.new { CType::Immediate.parse("char") }, Primitive.cexpr!("OFFSETOF((*((struct mjit_options *)NULL)), debug_flags)")],
       wait: [self._Bool, Primitive.cexpr!("OFFSETOF((*((struct mjit_options *)NULL)), wait)")],
-      min_calls: [CType::Immediate.parse("unsigned int"), Primitive.cexpr!("OFFSETOF((*((struct mjit_options *)NULL)), min_calls)")],
+      call_threshold: [CType::Immediate.parse("unsigned int"), Primitive.cexpr!("OFFSETOF((*((struct mjit_options *)NULL)), call_threshold)")],
       verbose: [CType::Immediate.parse("int"), Primitive.cexpr!("OFFSETOF((*((struct mjit_options *)NULL)), verbose)")],
       max_cache_size: [CType::Immediate.parse("int"), Primitive.cexpr!("OFFSETOF((*((struct mjit_options *)NULL)), max_cache_size)")],
       pause: [self._Bool, Primitive.cexpr!("OFFSETOF((*((struct mjit_options *)NULL)), pause)")],
@@ -569,7 +565,7 @@ def C.rb_iseq_t
   def C.rb_method_definition_struct
     @rb_method_definition_struct ||= CType::Struct.new(
       "rb_method_definition_struct", Primitive.cexpr!("SIZEOF(struct rb_method_definition_struct)"),
-      type: [self.rb_method_type_t, 0],
+      type: [CType::BitField.new(4, 0), 0],
       iseq_overload: [CType::BitField.new(1, 4), 4],
       alias_count: [CType::BitField.new(27, 5), 5],
       complemented_count: [CType::BitField.new(28, 0), 32],
diff --git a/node.h b/node.h
index 39427257ddc466..220de3135e136e 100644
--- a/node.h
+++ b/node.h
@@ -461,6 +461,7 @@ struct rb_args_info {
     NODE *opt_args;
     unsigned int no_kwarg: 1;
     unsigned int ruby2_keywords: 1;
+    unsigned int forwarding: 1;
 
     VALUE imemo;
 };
diff --git a/numeric.c b/numeric.c
index 8607d697942a3a..b191b25d79e041 100644
--- a/numeric.c
+++ b/numeric.c
@@ -449,7 +449,7 @@ static int
 do_coerce(VALUE *x, VALUE *y, int err)
 {
     VALUE ary = rb_check_funcall(*y, id_coerce, 1, x);
-    if (ary == Qundef) {
+    if (UNDEF_P(ary)) {
         if (err) {
             coerce_failed(*x, *y);
         }
@@ -1713,7 +1713,7 @@ flo_cmp(VALUE x, VALUE y)
         b = RFLOAT_VALUE(y);
     }
     else {
-        if (isinf(a) && (i = rb_check_funcall(y, rb_intern("infinite?"), 0, 0)) != Qundef) {
+        if (isinf(a) && !UNDEF_P(i = rb_check_funcall(y, rb_intern("infinite?"), 0, 0))) {
             if (RTEST(i)) {
                 int j = rb_cmpint(i, x, y);
                 j = (a > 0.0) ? (j > 0 ? 0 : +1) : (j < 0 ? 0 : -1);
@@ -2858,7 +2858,7 @@ num_step_negative_p(VALUE num)
     }
 
     r = rb_check_funcall(num, '>', 1, &zero);
-    if (r == Qundef) {
+    if (UNDEF_P(r)) {
         coerce_failed(num, INT2FIX(0));
     }
     return !RTEST(r);
@@ -2876,11 +2876,11 @@ num_step_extract_args(int argc, const VALUE *argv, VALUE *to, VALUE *step, VALUE
         keys[0] = id_to;
         keys[1] = id_by;
         rb_get_kwargs(hash, keys, 0, 2, values);
-        if (values[0] != Qundef) {
+        if (!UNDEF_P(values[0])) {
             if (argc > 0) rb_raise(rb_eArgError, "to is given twice");
             *to = values[0];
         }
-        if (values[1] != Qundef) {
+        if (!UNDEF_P(values[1])) {
             if (argc > 1) rb_raise(rb_eArgError, "step is given twice");
             *by = values[1];
         }
@@ -2893,7 +2893,7 @@ static int
 num_step_check_fix_args(int argc, VALUE *to, VALUE *step, VALUE by, int fix_nil, int allow_zero_step)
 {
     int desc;
-    if (by != Qundef) {
+    if (!UNDEF_P(by)) {
         *step = by;
     }
     else {
@@ -3041,7 +3041,7 @@ num_step(int argc, VALUE *argv, VALUE from)
         VALUE by = Qundef;
 
         num_step_extract_args(argc, argv, &to, &step, &by);
-        if (by != Qundef) {
+        if (!UNDEF_P(by)) {
             step = by;
         }
         if (NIL_P(step)) {
@@ -4930,7 +4930,7 @@ rb_num_coerce_bit(VALUE x, VALUE y, ID func)
     do_coerce(&args[1], &args[2], TRUE);
     ret = rb_exec_recursive_paired(num_funcall_bit_1,
                                    args[2], args[1], (VALUE)args);
-    if (ret == Qundef) {
+    if (UNDEF_P(ret)) {
         /* show the original object, not coerced object */
         coerce_failed(x, y);
     }
diff --git a/object.c b/object.c
index 6251dacae22dd9..c28e96ed362c76 100644
--- a/object.c
+++ b/object.c
@@ -129,7 +129,7 @@ rb_equal(VALUE obj1, VALUE obj2)
 
     if (obj1 == obj2) return Qtrue;
     result = rb_equal_opt(obj1, obj2);
-    if (result == Qundef) {
+    if (UNDEF_P(result)) {
         result = rb_funcall(obj1, id_eq, 1, obj2);
     }
     return RBOOL(RTEST(result));
@@ -142,7 +142,7 @@ rb_eql(VALUE obj1, VALUE obj2)
 
     if (obj1 == obj2) return TRUE;
     result = rb_eql_opt(obj1, obj2);
-    if (result == Qundef) {
+    if (UNDEF_P(result)) {
         result = rb_funcall(obj1, id_eql, 1, obj2);
     }
     return RTEST(result);
@@ -297,7 +297,7 @@ rb_obj_copy_ivar(VALUE dest, VALUE obj)
     rb_shape_t * initial_shape = rb_shape_get_shape(dest);
 
     if (initial_shape->size_pool_index != src_shape->size_pool_index) {
-        RUBY_ASSERT(initial_shape->parent_id == ROOT_SHAPE_ID || initial_shape->type == SHAPE_ROOT);
+        RUBY_ASSERT(initial_shape->type == SHAPE_T_OBJECT);
 
         shape_to_set_on_dest = rb_shape_rebuild_shape(initial_shape, src_shape);
     }
@@ -310,7 +310,7 @@ rb_obj_copy_ivar(VALUE dest, VALUE obj)
         rb_shape_t * initial_shape = rb_shape_get_shape(dest);
 
         if (initial_shape->size_pool_index != src_shape->size_pool_index) {
-            RUBY_ASSERT(initial_shape->parent_id == ROOT_SHAPE_ID || initial_shape->type == SHAPE_ROOT);
+            RUBY_ASSERT(initial_shape->type == SHAPE_T_OBJECT);
 
             shape_to_set_on_dest = rb_shape_rebuild_shape(initial_shape, src_shape);
         }
@@ -421,7 +421,7 @@ rb_get_freeze_opt(int argc, VALUE *argv)
     rb_scan_args(argc, argv, "0:", &opt);
     if (!NIL_P(opt)) {
         rb_get_kwargs(opt, keyword_ids, 0, 1, &kwfreeze);
-        if (kwfreeze != Qundef)
+        if (!UNDEF_P(kwfreeze))
             kwfreeze = obj_freeze_opt(kwfreeze);
     }
     return kwfreeze;
@@ -2555,7 +2555,7 @@ rb_mod_const_defined(int argc, VALUE *argv, VALUE mod)
 
 #if 0
         mod = rb_const_search(mod, id, beglen > 0 || !RTEST(recur), RTEST(recur), FALSE);
-        if (mod == Qundef) return Qfalse;
+        if (UNDEF_P(mod)) return Qfalse;
 #else
         if (!RTEST(recur)) {
             if (!rb_const_defined_at(mod, id))
@@ -2985,7 +2985,7 @@ static VALUE
 convert_type_with_id(VALUE val, const char *tname, ID method, int raise, int index)
 {
     VALUE r = rb_check_funcall(val, method, 0, 0);
-    if (r == Qundef) {
+    if (UNDEF_P(r)) {
         if (raise) {
             const char *msg =
                 ((index < 0 ? conv_method_index(rb_id2name(method)) : index)
diff --git a/parse.y b/parse.y
index 526a25ac3b861d..846136bd0363de 100644
--- a/parse.y
+++ b/parse.y
@@ -5322,6 +5322,9 @@ args_tail	: f_kwarg ',' f_kwrest opt_f_block_arg
 		    {
 			add_forwarding_args(p);
 			$$ = new_args_tail(p, Qnone, $1, ID2VAL(idFWD_BLOCK), &@1);
+		    /*%%%*/
+			($$->nd_ainfo)->forwarding = 1;
+		    /*% %*/
 		    }
 		;
 
@@ -5612,7 +5615,7 @@ f_kwrest	: kwrest_mark tIDENTIFIER
 		    {
 			arg_var(p, ANON_KEYWORD_REST_ID);
 		    /*%%%*/
-			$$ = internal_id(p);
+			$$ = ANON_KEYWORD_REST_ID;
 		    /*% %*/
 		    /*% ripper: kwrest_param!(Qnil) %*/
 		    }
@@ -5688,7 +5691,7 @@ f_rest_arg	: restarg_mark tIDENTIFIER
 		    {
 			arg_var(p, ANON_REST_ID);
 		    /*%%%*/
-			$$ = internal_id(p);
+			$$ = ANON_REST_ID;
 		    /*% %*/
 		    /*% ripper: rest_param!(Qnil) %*/
 		    }
@@ -5710,7 +5713,7 @@ f_block_arg	: blkarg_mark tIDENTIFIER
                     {
 			arg_var(p, ANON_BLOCK_ID);
                     /*%%%*/
-			$$ = internal_id(p);
+			$$ = ANON_BLOCK_ID;
                     /*% %*/
 		    /*% ripper: blockarg!(Qnil) %*/
                     }
@@ -10848,7 +10851,7 @@ check_literal_when(struct parser_params *p, NODE *arg, const YYLTYPE *loc)
     if (!arg || !p->case_labels) return;
 
     lit = rb_node_case_when_optimizable_literal(arg);
-    if (lit == Qundef) return;
+    if (UNDEF_P(lit)) return;
     if (nd_type_p(arg, NODE_STR)) {
 	RB_OBJ_WRITTEN(p->ast, Qnil, arg->nd_lit = lit);
     }
@@ -11501,7 +11504,7 @@ shareable_literal_constant(struct parser_params *p, enum shareability shareable,
 	    }
 	    if (RTEST(lit)) {
 		VALUE e = shareable_literal_value(elt);
-		if (e != Qundef) {
+		if (!UNDEF_P(e)) {
 		    rb_ary_push(lit, e);
 		}
 		else {
@@ -11541,7 +11544,7 @@ shareable_literal_constant(struct parser_params *p, enum shareability shareable,
 	    if (RTEST(lit)) {
 		VALUE k = shareable_literal_value(key);
 		VALUE v = shareable_literal_value(val);
-		if (k != Qundef && v != Qundef) {
+		if (!UNDEF_P(k) && !UNDEF_P(v)) {
 		    rb_hash_aset(lit, k, v);
 		}
 		else {
@@ -12204,7 +12207,7 @@ new_args(struct parser_params *p, NODE *pre_args, NODE *opt_args, ID rest_arg, N
     int saved_line = p->ruby_sourceline;
     struct rb_args_info *args = tail->nd_ainfo;
 
-    if (args->block_arg == idFWD_BLOCK) {
+    if (args->forwarding) {
 	if (rest_arg) {
 	    yyerror1(&tail->nd_loc, "... after rest argument");
 	    return tail;
@@ -12223,7 +12226,7 @@ new_args(struct parser_params *p, NODE *pre_args, NODE *opt_args, ID rest_arg, N
 
     args->opt_args       = opt_args;
 
-    args->ruby2_keywords = rest_arg == idFWD_REST;
+    args->ruby2_keywords = args->forwarding;
 
     p->ruby_sourceline = saved_line;
     nd_set_loc(tail, loc);
@@ -13787,7 +13790,7 @@ ripper_validate_object(VALUE self, VALUE x)
     if (x == Qfalse) return x;
     if (x == Qtrue) return x;
     if (NIL_P(x)) return x;
-    if (x == Qundef)
+    if (UNDEF_P(x))
 	rb_raise(rb_eArgError, "Qundef given");
     if (FIXNUM_P(x)) return x;
     if (SYMBOL_P(x)) return x;
@@ -13898,7 +13901,7 @@ static VALUE
 ripper_get_value(VALUE v)
 {
     NODE *nd;
-    if (v == Qundef) return Qnil;
+    if (UNDEF_P(v)) return Qnil;
     if (!RB_TYPE_P(v, T_NODE)) return v;
     nd = (NODE *)v;
     if (!nd_type_p(nd, NODE_RIPPER)) return Qnil;
@@ -14159,7 +14162,7 @@ static VALUE
 ripper_assert_Qundef(VALUE self, VALUE obj, VALUE msg)
 {
     StringValue(msg);
-    if (obj == Qundef) {
+    if (UNDEF_P(obj)) {
         rb_raise(rb_eArgError, "%"PRIsVALUE, msg);
     }
     return Qnil;
diff --git a/proc.c b/proc.c
index a25786c0157251..71b6f1ef803606 100644
--- a/proc.c
+++ b/proc.c
@@ -89,7 +89,7 @@ block_mark(const struct rb_block *block)
             const struct rb_captured_block *captured = &block->as.captured;
             RUBY_MARK_MOVABLE_UNLESS_NULL(captured->self);
             RUBY_MARK_MOVABLE_UNLESS_NULL((VALUE)captured->code.val);
-            if (captured->ep && captured->ep[VM_ENV_DATA_INDEX_ENV] != Qundef /* cfunc_proc_t */) {
+            if (captured->ep && !UNDEF_P(captured->ep[VM_ENV_DATA_INDEX_ENV]) /* cfunc_proc_t */) {
                 rb_gc_mark(VM_ENV_ENVVAL(captured->ep));
             }
         }
@@ -1645,7 +1645,7 @@ respond_to_missing_p(VALUE klass, VALUE obj, VALUE sym, int scope)
     /* TODO: merge with obj_respond_to() */
     ID rmiss = idRespond_to_missing;
 
-    if (obj == Qundef) return 0;
+    if (UNDEF_P(obj)) return 0;
     if (rb_method_basic_definition_p(klass, rmiss)) return 0;
     return RTEST(rb_funcall(obj, rmiss, 2, sym, RBOOL(!scope)));
 }
@@ -1746,7 +1746,7 @@ mnew_callable(VALUE klass, VALUE obj, ID id, VALUE mclass, int scope)
     const rb_method_entry_t *me;
     VALUE iclass = Qnil;
 
-    ASSUME(obj != Qundef);
+    ASSUME(!UNDEF_P(obj));
     me = (rb_method_entry_t *)rb_callable_method_entry_with_refinements(klass, id, &iclass);
     return mnew_from_me(me, klass, iclass, obj, id, mclass, scope);
 }
@@ -1988,7 +1988,7 @@ rb_method_name_error(VALUE klass, VALUE str)
     else if (RB_TYPE_P(c, T_MODULE)) {
         s = MSG(" module");
     }
-    if (s == Qundef) {
+    if (UNDEF_P(s)) {
         s = MSG(" class");
     }
     rb_name_err_raise_str(s, c, str);
@@ -2493,7 +2493,7 @@ rb_method_call_with_block_kw(int argc, const VALUE *argv, VALUE method, VALUE pa
     rb_execution_context_t *ec = GET_EC();
 
     TypedData_Get_Struct(method, struct METHOD, &method_data_type, data);
-    if (data->recv == Qundef) {
+    if (UNDEF_P(data->recv)) {
         rb_raise(rb_eTypeError, "can't call unbound method; bind first");
     }
     return call_method_data(ec, data, argc, argv, passed_procval, kw_splat);
@@ -3142,7 +3142,7 @@ method_inspect(VALUE method)
     if (FL_TEST(mklass, FL_SINGLETON)) {
         VALUE v = rb_ivar_get(mklass, attached);
 
-        if (data->recv == Qundef) {
+        if (UNDEF_P(data->recv)) {
             rb_str_buf_append(str, rb_inspect(mklass));
         }
         else if (data->recv == v) {
diff --git a/process.c b/process.c
index d95b717960d097..dbe2be5b56fbe3 100644
--- a/process.c
+++ b/process.c
@@ -1332,7 +1332,7 @@ rb_process_status_wait(rb_pid_t pid, int flags)
     if (!(flags & WNOHANG)) {
         VALUE scheduler = rb_fiber_scheduler_current();
         VALUE result = rb_fiber_scheduler_process_wait(scheduler, pid, flags);
-        if (result != Qundef) return result;
+        if (!UNDEF_P(result)) return result;
     }
 
     struct waitpid_state waitpid_state;
@@ -3144,9 +3144,10 @@ NORETURN(static VALUE f_exec(int c, const VALUE *a, VALUE _));
  *  If the string from the first form (<code>exec("command")</code>) follows
  *  these simple rules:
  *
- *  * no meta characters
- *  * not starting with shell reserved word or special built-in
- *  * Ruby invokes the command directly without shell
+ *  * no meta characters,
+ *  * not starting with shell reserved word or special built-in,
+ *
+ *  Ruby invokes the command directly without shell.
  *
  *  You can force shell invocation by adding ";" to the string (because ";" is
  *  a meta character).
diff --git a/ractor.c b/ractor.c
index 3569202e58ee27..3605da74e6ffda 100644
--- a/ractor.c
+++ b/ractor.c
@@ -728,7 +728,7 @@ ractor_receive(rb_execution_context_t *ec, rb_ractor_t *cr)
     VM_ASSERT(cr == rb_ec_ractor_ptr(ec));
     VALUE v;
 
-    while ((v = ractor_try_receive(ec, cr)) == Qundef) {
+    while (UNDEF_P(v = ractor_try_receive(ec, cr))) {
         ractor_receive_wait(ec, cr);
     }
 
@@ -875,7 +875,7 @@ ractor_receive_if(rb_execution_context_t *ec, VALUE crv, VALUE b)
         }
         RACTOR_UNLOCK_SELF(cr);
 
-        if (v != Qundef) {
+        if (!UNDEF_P(v)) {
             struct receive_block_data data = {
                 .cr = cr,
                 .rq = rq,
@@ -887,7 +887,7 @@ ractor_receive_if(rb_execution_context_t *ec, VALUE crv, VALUE b)
             VALUE result = rb_ensure(receive_if_body, (VALUE)&data,
                                      receive_if_ensure, (VALUE)&data);
 
-            if (result != Qundef) return result;
+            if (!UNDEF_P(result)) return result;
             index++;
         }
 
@@ -1095,7 +1095,7 @@ ractor_select(rb_execution_context_t *ec, const VALUE *rs, const int rs_len, VAL
     int i;
     bool interrupted = false;
     enum rb_ractor_wait_status wait_status = 0;
-    bool yield_p = (yielded_value != Qundef) ? true : false;
+    bool yield_p = !UNDEF_P(yielded_value) ? true : false;
     const int alen = rs_len + (yield_p ? 1 : 0);
 
     struct ractor_select_action {
@@ -1152,7 +1152,7 @@ ractor_select(rb_execution_context_t *ec, const VALUE *rs, const int rs_len, VAL
               case ractor_select_action_take:
                 rv = actions[i].v;
                 v = ractor_try_take(ec, RACTOR_PTR(rv));
-                if (v != Qundef) {
+                if (!UNDEF_P(v)) {
                     *ret_r = rv;
                     ret = v;
                     goto cleanup;
@@ -1160,7 +1160,7 @@ ractor_select(rb_execution_context_t *ec, const VALUE *rs, const int rs_len, VAL
                 break;
               case ractor_select_action_receive:
                 v = ractor_try_receive(ec, cr);
-                if (v != Qundef) {
+                if (!UNDEF_P(v)) {
                     *ret_r = ID2SYM(rb_intern("receive"));
                     ret = v;
                     goto cleanup;
@@ -1324,7 +1324,7 @@ ractor_select(rb_execution_context_t *ec, const VALUE *rs, const int rs_len, VAL
         goto restart;
     }
 
-    VM_ASSERT(ret != Qundef);
+    VM_ASSERT(!UNDEF_P(ret));
     return ret;
 }
 
@@ -2289,7 +2289,7 @@ obj_traverse_i(VALUE obj, struct obj_traverse_data *data)
         rb_ivar_generic_ivtbl_lookup(obj, &ivtbl);
         for (uint32_t i = 0; i < ivtbl->numiv; i++) {
             VALUE val = ivtbl->ivptr[i];
-            if (val != Qundef && obj_traverse_i(val, data)) return 1;
+            if (!UNDEF_P(val) && obj_traverse_i(val, data)) return 1;
         }
     }
 
@@ -2311,7 +2311,7 @@ obj_traverse_i(VALUE obj, struct obj_traverse_data *data)
 
             for (uint32_t i=0; i<len; i++) {
                 VALUE val = ptr[i];
-                if (val != Qundef && obj_traverse_i(val, data)) return 1;
+                if (!UNDEF_P(val) && obj_traverse_i(val, data)) return 1;
             }
         }
         break;
@@ -2735,7 +2735,7 @@ obj_traverse_replace_i(VALUE obj, struct obj_traverse_replace_data *data)
         struct gen_ivtbl *ivtbl;
         rb_ivar_generic_ivtbl_lookup(obj, &ivtbl);
         for (uint32_t i = 0; i < ivtbl->numiv; i++) {
-            if (ivtbl->ivptr[i] != Qundef) {
+            if (!UNDEF_P(ivtbl->ivptr[i])) {
                 CHECK_AND_REPLACE(ivtbl->ivptr[i]);
             }
         }
@@ -2764,7 +2764,7 @@ obj_traverse_replace_i(VALUE obj, struct obj_traverse_replace_data *data)
             VALUE *ptr = ROBJECT_IVPTR(obj);
 
             for (uint32_t i=0; i<len; i++) {
-                if (ptr[i] != Qundef) {
+                if (!UNDEF_P(ptr[i])) {
                     CHECK_AND_REPLACE(ptr[i]);
                 }
             }
@@ -2969,7 +2969,7 @@ static VALUE
 ractor_move(VALUE obj)
 {
     VALUE val = rb_obj_traverse_replace(obj, move_enter, move_leave, true);
-    if (val != Qundef) {
+    if (!UNDEF_P(val)) {
         return val;
     }
     else {
@@ -3000,7 +3000,7 @@ static VALUE
 ractor_copy(VALUE obj)
 {
     VALUE val = rb_obj_traverse_replace(obj, copy_enter, copy_leave, false);
-    if (val != Qundef) {
+    if (!UNDEF_P(val)) {
         return val;
     }
     else {
@@ -3132,7 +3132,7 @@ static bool
 ractor_local_ref(rb_ractor_local_key_t key, void **pret)
 {
     if (rb_ractor_main_p()) {
-        if ((VALUE)key->main_cache != Qundef) {
+        if (!UNDEF_P((VALUE)key->main_cache)) {
             *pret = key->main_cache;
             return true;
         }
diff --git a/ractor_core.h b/ractor_core.h
index 9d4b8387c734b0..294708fcb8ad1e 100644
--- a/ractor_core.h
+++ b/ractor_core.h
@@ -290,7 +290,7 @@ rb_ractor_id(const rb_ractor_t *r)
 #if RACTOR_CHECK_MODE > 0
 uint32_t rb_ractor_current_id(void);
 // If ractor check mode is enabled, shape bits needs to be smaller
-STATIC_ASSERT(shape_bits, SHAPE_BITS == 16);
+STATIC_ASSERT(shape_bits, SHAPE_ID_NUM_BITS == 16);
 
 static inline void
 rb_ractor_setup_belonging_to(VALUE obj, uint32_t rid)
diff --git a/range.c b/range.c
index a2c0e218600607..0c3dc51c73b520 100644
--- a/range.c
+++ b/range.c
@@ -607,7 +607,7 @@ is_integer_p(VALUE v)
     VALUE is_int;
     CONST_ID(id_integer_p, "integer?");
     is_int = rb_check_funcall(v, id_integer_p, 0, 0);
-    return RTEST(is_int) && is_int != Qundef;
+    return RTEST(is_int) && !UNDEF_P(is_int);
 }
 
 static VALUE
@@ -1505,11 +1505,11 @@ rb_range_values(VALUE range, VALUE *begp, VALUE *endp, int *exclp)
     else {
         VALUE x;
         b = rb_check_funcall(range, id_beg, 0, 0);
-        if (b == Qundef) return (int)Qfalse;
+        if (UNDEF_P(b)) return (int)Qfalse;
         e = rb_check_funcall(range, id_end, 0, 0);
-        if (e == Qundef) return (int)Qfalse;
+        if (UNDEF_P(e)) return (int)Qfalse;
         x = rb_check_funcall(range, rb_intern("exclude_end?"), 0, 0);
-        if (x == Qundef) return (int)Qfalse;
+        if (UNDEF_P(x)) return (int)Qfalse;
         excl = RTEST(x);
     }
     *begp = b;
@@ -1646,7 +1646,7 @@ inspect_range(VALUE range, VALUE dummy, int recur)
     if (NIL_P(RANGE_BEG(range)) || !NIL_P(RANGE_END(range))) {
         str2 = rb_inspect(RANGE_END(range));
     }
-    if (str2 != Qundef) rb_str_append(str, str2);
+    if (!UNDEF_P(str2)) rb_str_append(str, str2);
 
     return str;
 }
@@ -1724,7 +1724,7 @@ static VALUE
 range_eqq(VALUE range, VALUE val)
 {
     VALUE ret = range_include_internal(range, val, 1);
-    if (ret != Qundef) return ret;
+    if (!UNDEF_P(ret)) return ret;
     return r_cover_p(range, RANGE_BEG(range), RANGE_END(range), val);
 }
 
@@ -1764,7 +1764,7 @@ static VALUE
 range_include(VALUE range, VALUE val)
 {
     VALUE ret = range_include_internal(range, val, 0);
-    if (ret != Qundef) return ret;
+    if (!UNDEF_P(ret)) return ret;
     return rb_call_super(1, &val);
 }
 
diff --git a/rational.c b/rational.c
index 48a9ab2ed28932..dfe2ad74eb7b9b 100644
--- a/rational.c
+++ b/rational.c
@@ -2552,7 +2552,7 @@ nurat_convert(VALUE klass, VALUE numv, VALUE denv, int raise)
     VALUE a1 = numv, a2 = denv;
     int state;
 
-    assert(a1 != Qundef);
+    assert(!UNDEF_P(a1));
 
     if (NIL_P(a1) || NIL_P(a2)) {
         if (!raise) return Qnil;
@@ -2603,7 +2603,7 @@ nurat_convert(VALUE klass, VALUE numv, VALUE denv, int raise)
         a2 = string_to_r_strict(a2, raise);
         if (!raise && NIL_P(a2)) return Qnil;
     }
-    else if (a2 != Qundef && !rb_respond_to(a2, idTo_r)) {
+    else if (!UNDEF_P(a2) && !rb_respond_to(a2, idTo_r)) {
         VALUE tmp = rb_protect(rb_check_to_int, a2, NULL);
         rb_set_errinfo(Qnil);
         if (!NIL_P(tmp)) {
@@ -2612,11 +2612,11 @@ nurat_convert(VALUE klass, VALUE numv, VALUE denv, int raise)
     }
 
     if (RB_TYPE_P(a1, T_RATIONAL)) {
-        if (a2 == Qundef || (k_exact_one_p(a2)))
+        if (UNDEF_P(a2) || (k_exact_one_p(a2)))
             return a1;
     }
 
-    if (a2 == Qundef) {
+    if (UNDEF_P(a2)) {
         if (!RB_INTEGER_TYPE_P(a1)) {
             if (!raise) {
                 VALUE result = rb_protect(to_rational, a1, NULL);
@@ -2666,7 +2666,7 @@ nurat_convert(VALUE klass, VALUE numv, VALUE denv, int raise)
 
     a1 = nurat_int_value(a1);
 
-    if (a2 == Qundef) {
+    if (UNDEF_P(a2)) {
         a2 = ONE;
     }
     else if (!k_integer_p(a2) && !raise) {
diff --git a/re.c b/re.c
index 1b8314832156a5..15fe10b6af725c 100644
--- a/re.c
+++ b/re.c
@@ -3832,14 +3832,14 @@ rb_reg_initialize_m(int argc, VALUE *argv, VALUE self)
         str = RREGEXP_SRC(re);
     }
     else {
-        if (opts != Qundef) {
+        if (!UNDEF_P(opts)) {
             int f;
             if (FIXNUM_P(opts)) flags = FIX2INT(opts);
             else if ((f = str_to_option(opts)) >= 0) flags = f;
             else if (!NIL_P(opts) && rb_bool_expected(opts, "ignorecase", FALSE))
                 flags = ONIG_OPTION_IGNORECASE;
         }
-        if (n_flag != Qundef && !NIL_P(n_flag)) {
+        if (!UNDEF_P(n_flag) && !NIL_P(n_flag)) {
             char *kcode = StringValuePtr(n_flag);
             if (kcode[0] == 'n' || kcode[0] == 'N') {
                 enc = rb_ascii8bit_encoding();
diff --git a/regexec.c b/regexec.c
index 75ffb86c4510dc..f7c5d12133ff5b 100644
--- a/regexec.c
+++ b/regexec.c
@@ -234,10 +234,8 @@ onig_get_capture_tree(OnigRegion* region)
 #ifdef USE_CACHE_MATCH_OPT
 
 /* count number of jump-like opcodes for allocation of cache memory. */
-/* return -1 if we cannot optimize the regex matching by using cache. */
-static long count_num_cache_opcode(regex_t* reg, long* table_size)
+static OnigPosition count_num_cache_opcode(regex_t* reg, long* num, long* table_size)
 {
-  long num = 0;
   UChar* p = reg->p;
   UChar* pend = p + reg->used;
   LengthType len;
@@ -246,6 +244,9 @@ static long count_num_cache_opcode(regex_t* reg, long* table_size)
   long current_mem_num = 0;
   OnigEncoding enc = reg->enc;
 
+  *num = 0;
+  *table_size = 0;
+
   while (p < pend) {
     switch (*p++) {
       case OP_FINISH:
@@ -298,10 +299,10 @@ static long count_num_cache_opcode(regex_t* reg, long* table_size)
 	break;
       case OP_ANYCHAR_STAR:
       case OP_ANYCHAR_ML_STAR:
-	num++; *table_size += 1; break;
+	*num += 1; *table_size += 1; break;
       case OP_ANYCHAR_STAR_PEEK_NEXT:
       case OP_ANYCHAR_ML_STAR_PEEK_NEXT:
-	p++; num++; *table_size += 1; break;
+	p++; *num += 1; *table_size += 1; break;
 
       case OP_WORD:
       case OP_NOT_WORD:
@@ -334,7 +335,7 @@ static long count_num_cache_opcode(regex_t* reg, long* table_size)
       case OP_BACKREF_MULTI:
       case OP_BACKREF_MULTI_IC:
       case OP_BACKREF_WITH_LEVEL:
-	return NUM_CACHE_OPCODE_FAIL;
+	goto fail;
 
       case OP_MEMORY_START:
       case OP_MEMORY_START_PUSH:
@@ -354,43 +355,43 @@ static long count_num_cache_opcode(regex_t* reg, long* table_size)
 	break;
       case OP_PUSH:
         p += SIZE_RELADDR;
-	num++;
+	*num += 1;
 	*table_size += 1;
 	break;
       case OP_POP:
 	break;
       case OP_PUSH_OR_JUMP_EXACT1:
       case OP_PUSH_IF_PEEK_NEXT:
-	p += SIZE_RELADDR + 1; num++; *table_size += 1; break;
+	p += SIZE_RELADDR + 1; *num += 1; *table_size += 1; break;
       case OP_REPEAT:
       case OP_REPEAT_NG:
 	if (current_mem != -1) {
 	  // A nested OP_REPEAT is not yet supported.
-	  return NUM_CACHE_OPCODE_FAIL;
+	  goto fail;
 	}
 	GET_MEMNUM_INC(mem, p);
 	p += SIZE_RELADDR;
 	if (reg->repeat_range[mem].lower == 0) {
-	  num++;
+	  *num += 1;
 	  *table_size += 1;
 	}
-	reg->repeat_range[mem].base_num = num;
+	reg->repeat_range[mem].base_num = *num;
 	current_mem = mem;
-	current_mem_num = num;
+	current_mem_num = *num;
 	break;
       case OP_REPEAT_INC:
       case OP_REPEAT_INC_NG:
         GET_MEMNUM_INC(mem, p);
 	if (mem != current_mem) {
 	  // A lone or invalid OP_REPEAT_INC is found.
-	  return NUM_CACHE_OPCODE_FAIL;
+	  goto fail;
 	}
 	{
-	  long inner_num = num - current_mem_num;
+	  long inner_num = *num - current_mem_num;
 	  OnigRepeatRange *repeat_range = &reg->repeat_range[mem];
 	  repeat_range->inner_num = inner_num;
-	  num -= inner_num;
-	  num += inner_num * repeat_range->lower + (inner_num + 1) * (repeat_range->upper == 0x7fffffff ? 1 : repeat_range->upper - repeat_range->lower);
+	  *num -= inner_num;
+	  *num += inner_num * repeat_range->lower + (inner_num + 1) * (repeat_range->upper == 0x7fffffff ? 1 : repeat_range->upper - repeat_range->lower);
 	  if (repeat_range->lower < repeat_range->upper) {
 	    *table_size += 1;
 	  }
@@ -401,7 +402,7 @@ static long count_num_cache_opcode(regex_t* reg, long* table_size)
       case OP_REPEAT_INC_SG:
       case OP_REPEAT_INC_NG_SG:
 	// TODO: Support nested OP_REPEAT.
-	return NUM_CACHE_OPCODE_FAIL;
+	goto fail;
       case OP_NULL_CHECK_START:
       case OP_NULL_CHECK_END:
       case OP_NULL_CHECK_END_MEMST:
@@ -420,33 +421,43 @@ static long count_num_cache_opcode(regex_t* reg, long* table_size)
       case OP_PUSH_ABSENT_POS:
       case OP_ABSENT_END:
       case OP_ABSENT:
-	return NUM_CACHE_OPCODE_FAIL;
+	goto fail;
 
       case OP_CALL:
       case OP_RETURN:
-	return NUM_CACHE_OPCODE_FAIL;
+	goto fail;
 
       case OP_CONDITION:
-	return NUM_CACHE_OPCODE_FAIL;
+	goto fail;
 
       case OP_STATE_CHECK_PUSH:
       case OP_STATE_CHECK_PUSH_OR_JUMP:
       case OP_STATE_CHECK:
       case OP_STATE_CHECK_ANYCHAR_STAR:
       case OP_STATE_CHECK_ANYCHAR_ML_STAR:
-	return NUM_CACHE_OPCODE_FAIL;
+	goto fail;
 
       case OP_SET_OPTION_PUSH:
       case OP_SET_OPTION:
 	p += SIZE_OPTION;
 	break;
+
+      default:
+        goto bytecode_error;
     }
   }
 
-  return num;
+  return 0;
+
+fail:
+  *num = NUM_CACHE_OPCODE_FAIL;
+  return 0;
+
+bytecode_error:
+  return ONIGERR_UNDEFINED_BYTECODE;
 }
 
-static void init_cache_index_table(regex_t* reg, OnigCacheIndex *table)
+static OnigPosition init_cache_index_table(regex_t* reg, OnigCacheIndex *table)
 {
   UChar* pbegin;
   UChar* p = reg->p;
@@ -496,6 +507,7 @@ static void init_cache_index_table(regex_t* reg, OnigCacheIndex *table)
       case OP_CCLASS:
       case OP_CCLASS_NOT:
         p += SIZE_BITSET; break;
+      case OP_CCLASS_MB:
       case OP_CCLASS_MB_NOT:
 	GET_LENGTH_INC(len, p); p += len; break;
       case OP_CCLASS_MIX:
@@ -557,7 +569,7 @@ static void init_cache_index_table(regex_t* reg, OnigCacheIndex *table)
       case OP_BACKREF_MULTI:
       case OP_BACKREF_MULTI_IC:
       case OP_BACKREF_WITH_LEVEL:
-	return;
+	goto unexpected_bytecode_error;
 
       case OP_MEMORY_START:
       case OP_MEMORY_START_PUSH:
@@ -629,7 +641,7 @@ static void init_cache_index_table(regex_t* reg, OnigCacheIndex *table)
       case OP_REPEAT_INC_SG:
       case OP_REPEAT_INC_NG_SG:
 	// TODO: support OP_REPEAT opcodes.
-	return;
+	goto unexpected_bytecode_error;
       case OP_NULL_CHECK_START:
       case OP_NULL_CHECK_END:
       case OP_NULL_CHECK_END_MEMST:
@@ -648,28 +660,39 @@ static void init_cache_index_table(regex_t* reg, OnigCacheIndex *table)
       case OP_PUSH_ABSENT_POS:
       case OP_ABSENT_END:
       case OP_ABSENT:
-	return;
+	goto unexpected_bytecode_error;
 
       case OP_CALL:
       case OP_RETURN:
-	return;
+	goto unexpected_bytecode_error;
 
       case OP_CONDITION:
-	return;
+	goto unexpected_bytecode_error;
 
       case OP_STATE_CHECK_PUSH:
       case OP_STATE_CHECK_PUSH_OR_JUMP:
       case OP_STATE_CHECK:
       case OP_STATE_CHECK_ANYCHAR_STAR:
       case OP_STATE_CHECK_ANYCHAR_ML_STAR:
-	return;
+	goto unexpected_bytecode_error;
 
       case OP_SET_OPTION_PUSH:
       case OP_SET_OPTION:
 	p += SIZE_OPTION;
 	break;
+
+      default:
+        goto bytecode_error;
     }
   }
+
+  return 0;
+
+unexpected_bytecode_error:
+  return ONIGERR_UNEXPECTED_BYTECODE;
+
+bytecode_error:
+  return ONIGERR_UNDEFINED_BYTECODE;
 }
 #endif /* USE_MATCH_CACHE */
 
@@ -860,6 +883,7 @@ onig_region_copy(OnigRegion* to, const OnigRegion* from)
   (msa).enable_cache_match_opt = 0;\
   (msa).num_fail = 0;\
   (msa).num_cache_opcode = NUM_CACHE_OPCODE_UNINIT;\
+  (msa).num_cache_table = 0;\
   (msa).cache_index_table = (OnigCacheIndex *)0;\
   (msa).match_cache = (uint8_t *)0;\
 } while(0)
@@ -3819,23 +3843,26 @@ match_at(regex_t* reg, const UChar* str, const UChar* end,
 
 #ifdef USE_CACHE_MATCH_OPT
       if (++msa->num_fail >= (long)(end - str) + 1 && msa->num_cache_opcode == NUM_CACHE_OPCODE_UNINIT) {
-	long table_size = 0;
 	msa->enable_cache_match_opt = 1;
 	if (msa->num_cache_opcode == NUM_CACHE_OPCODE_UNINIT) {
-	  msa->num_cache_opcode = count_num_cache_opcode(reg, &table_size);
+	  OnigPosition r = count_num_cache_opcode(reg, &msa->num_cache_opcode, &msa->num_cache_table);
+          if (r < 0) goto bytecode_error;
 	}
 	if (msa->num_cache_opcode == NUM_CACHE_OPCODE_FAIL || msa->num_cache_opcode == 0) {
 	  msa->enable_cache_match_opt = 0;
 	  goto fail_match_cache_opt;
 	}
 	if (msa->cache_index_table == NULL) {
-	  OnigCacheIndex *table = (OnigCacheIndex *)xmalloc(table_size * sizeof(OnigCacheIndex));
+	  OnigCacheIndex *table = (OnigCacheIndex *)xmalloc(msa->num_cache_table * sizeof(OnigCacheIndex));
 	  if (table == NULL) {
 	    return ONIGERR_MEMORY;
 	  }
-	  init_cache_index_table(reg, table);
+	  OnigPosition r = init_cache_index_table(reg, table);
+          if (r < 0) {
+            if (r == ONIGERR_UNEXPECTED_BYTECODE) goto unexpected_bytecode_error;
+            else goto bytecode_error;
+          }
 	  msa->cache_index_table = table;
-	  msa->num_cache_table = table_size;
 	}
 	size_t len = (end - str) + 1;
 	size_t match_cache_size8 = (size_t)msa->num_cache_opcode * len;
diff --git a/scheduler.c b/scheduler.c
index 611182741c664b..9f28ae0eb6dffb 100644
--- a/scheduler.c
+++ b/scheduler.c
@@ -231,10 +231,10 @@ rb_fiber_scheduler_close(VALUE scheduler)
     // would create an infinite loop.
 
     result = rb_check_funcall(scheduler, id_scheduler_close, 0, NULL);
-    if (result != Qundef) return result;
+    if (!UNDEF_P(result)) return result;
 
     result = rb_check_funcall(scheduler, id_close, 0, NULL);
-    if (result != Qundef) return result;
+    if (!UNDEF_P(result)) return result;
 
     return Qnil;
 }
diff --git a/shape.c b/shape.c
index 66f5f69a0c6de3..430bfeb90a4f49 100644
--- a/shape.c
+++ b/shape.c
@@ -8,6 +8,7 @@
 #include <stdbool.h>
 
 static ID id_frozen;
+static ID id_t_object;
 static ID size_pool_edge_names[SIZE_POOL_COUNT];
 
 /*
@@ -152,6 +153,7 @@ get_next_shape_internal(rb_shape_t * shape, ID id, enum shape_type shape_type)
                   case SHAPE_CAPACITY_CHANGE:
                   case SHAPE_IVAR_UNDEF:
                   case SHAPE_FROZEN:
+                  case SHAPE_T_OBJECT:
                     new_shape->next_iv_index = shape->next_iv_index;
                     break;
                   case SHAPE_INITIAL_CAPACITY:
@@ -264,6 +266,7 @@ rb_shape_get_iv_index(rb_shape_t * shape, ID id, attr_index_t *value)
               case SHAPE_IVAR_UNDEF:
               case SHAPE_ROOT:
               case SHAPE_INITIAL_CAPACITY:
+              case SHAPE_T_OBJECT:
                 return false;
               case SHAPE_FROZEN:
                 rb_bug("Ivar should not exist on transition\n");
@@ -322,10 +325,10 @@ rb_shape_set_shape(VALUE obj, rb_shape_t* shape)
     rb_shape_set_shape_id(obj, rb_shape_id(shape));
 }
 
-VALUE
-rb_shape_flags_mask(void)
+uint8_t
+rb_shape_id_num_bits(void)
 {
-    return SHAPE_FLAG_MASK;
+    return SHAPE_ID_NUM_BITS;
 }
 
 rb_shape_t *
@@ -333,29 +336,33 @@ rb_shape_rebuild_shape(rb_shape_t * initial_shape, rb_shape_t * dest_shape)
 {
     rb_shape_t * midway_shape;
 
-    if (dest_shape->type != SHAPE_ROOT) {
+    RUBY_ASSERT(initial_shape->type == SHAPE_T_OBJECT);
+
+    if (dest_shape->type != initial_shape->type) {
         midway_shape = rb_shape_rebuild_shape(initial_shape, rb_shape_get_parent(dest_shape));
     }
     else {
         midway_shape = initial_shape;
     }
 
-    switch (dest_shape->type) {
-        case SHAPE_IVAR:
-            if (midway_shape->capacity < midway_shape->next_iv_index) {
-                // There isn't enough room to write this IV, so we need to increase the capacity
-                midway_shape = rb_shape_transition_shape_capa(midway_shape, midway_shape->capacity * 2);
-            }
+    switch ((enum shape_type)dest_shape->type) {
+      case SHAPE_IVAR:
+        if (midway_shape->capacity <= midway_shape->next_iv_index) {
+            // There isn't enough room to write this IV, so we need to increase the capacity
+            midway_shape = rb_shape_transition_shape_capa(midway_shape, midway_shape->capacity * 2);
+        }
 
-            midway_shape = rb_shape_get_next_iv_shape(midway_shape, dest_shape->edge_name);
-            break;
-        case SHAPE_IVAR_UNDEF:
-            midway_shape = get_next_shape_internal(midway_shape, dest_shape->edge_name, SHAPE_IVAR_UNDEF);
-            break;
-        case SHAPE_ROOT:
-        case SHAPE_FROZEN:
-        case SHAPE_CAPACITY_CHANGE:
-            break;
+        midway_shape = rb_shape_get_next_iv_shape(midway_shape, dest_shape->edge_name);
+        break;
+      case SHAPE_IVAR_UNDEF:
+        midway_shape = get_next_shape_internal(midway_shape, dest_shape->edge_name, SHAPE_IVAR_UNDEF);
+        break;
+      case SHAPE_ROOT:
+      case SHAPE_FROZEN:
+      case SHAPE_CAPACITY_CHANGE:
+      case SHAPE_INITIAL_CAPACITY:
+      case SHAPE_T_OBJECT:
+        break;
     }
 
     return midway_shape;
@@ -592,6 +599,7 @@ void
 Init_default_shapes(void)
 {
     id_frozen = rb_make_internal_id();
+    id_t_object = rb_make_internal_id();
 
     // Shapes by size pool
     for (int i = 0; i < SIZE_POOL_COUNT; i++) {
@@ -615,6 +623,16 @@ Init_default_shapes(void)
         RUBY_ASSERT(rb_shape_id(new_shape) == (shape_id_t)i);
     }
 
+    // Make shapes for T_OBJECT
+    for (int i = 0; i < SIZE_POOL_COUNT; i++) {
+        rb_shape_t * shape = rb_shape_get_shape_by_id(i);
+#if RUBY_DEBUG
+        rb_shape_t * t_object_shape =
+#endif
+            get_next_shape_internal(shape, id_t_object, SHAPE_T_OBJECT);
+        RUBY_ASSERT(rb_shape_id(t_object_shape) == (shape_id_t)(i + SIZE_POOL_COUNT));
+    }
+
     // Special const shape
 #if RUBY_DEBUG
     rb_shape_t * special_const_shape =
@@ -644,9 +662,10 @@ Init_shape(void)
     rb_define_method(rb_cShape, "capacity", rb_shape_capacity, 0);
     rb_define_const(rb_cShape, "SHAPE_ROOT", INT2NUM(SHAPE_ROOT));
     rb_define_const(rb_cShape, "SHAPE_IVAR", INT2NUM(SHAPE_IVAR));
+    rb_define_const(rb_cShape, "SHAPE_T_OBJECT", INT2NUM(SHAPE_T_OBJECT));
     rb_define_const(rb_cShape, "SHAPE_IVAR_UNDEF", INT2NUM(SHAPE_IVAR_UNDEF));
     rb_define_const(rb_cShape, "SHAPE_FROZEN", INT2NUM(SHAPE_FROZEN));
-    rb_define_const(rb_cShape, "SHAPE_BITS", INT2NUM(SHAPE_BITS));
+    rb_define_const(rb_cShape, "SHAPE_ID_NUM_BITS", INT2NUM(SHAPE_ID_NUM_BITS));
     rb_define_const(rb_cShape, "SHAPE_FLAG_SHIFT", INT2NUM(SHAPE_FLAG_SHIFT));
     rb_define_const(rb_cShape, "SPECIAL_CONST_SHAPE_ID", INT2NUM(SPECIAL_CONST_SHAPE_ID));
 
diff --git a/shape.h b/shape.h
index a2cbd7c482ee86..43308b833baf20 100644
--- a/shape.h
+++ b/shape.h
@@ -15,25 +15,25 @@ typedef uint16_t attr_index_t;
 #if RUBY_DEBUG || (defined(VM_CHECK_MODE) && VM_CHECK_MODE > 0)
 #  if SIZEOF_SHAPE_T == 4
 typedef uint32_t shape_id_t;
-# define SHAPE_BITS 16
+# define SHAPE_ID_NUM_BITS 16
 #  else
 typedef uint16_t shape_id_t;
-# define SHAPE_BITS 16
+# define SHAPE_ID_NUM_BITS 16
 #  endif
 #else
 #  if SIZEOF_SHAPE_T == 4
 typedef uint32_t shape_id_t;
-# define SHAPE_BITS 32
+# define SHAPE_ID_NUM_BITS 32
 #  else
 typedef uint16_t shape_id_t;
-# define SHAPE_BITS 16
+# define SHAPE_ID_NUM_BITS 16
 #  endif
 #endif
 
-# define SHAPE_MASK (((uintptr_t)1 << SHAPE_BITS) - 1)
-# define SHAPE_FLAG_MASK (((VALUE)-1) >> SHAPE_BITS)
+# define SHAPE_MASK (((uintptr_t)1 << SHAPE_ID_NUM_BITS) - 1)
+# define SHAPE_FLAG_MASK (((VALUE)-1) >> SHAPE_ID_NUM_BITS)
 
-# define SHAPE_FLAG_SHIFT ((SIZEOF_VALUE * 8) - SHAPE_BITS)
+# define SHAPE_FLAG_SHIFT ((SIZEOF_VALUE * 8) - SHAPE_ID_NUM_BITS)
 
 # define SHAPE_BITMAP_SIZE 16384
 
@@ -42,7 +42,7 @@ typedef uint16_t shape_id_t;
 # define ROOT_SHAPE_ID 0x0
 // We use SIZE_POOL_COUNT number of shape IDs for transitions out of different size pools
 // The next available shapd ID will be the SPECIAL_CONST_SHAPE_ID
-# define SPECIAL_CONST_SHAPE_ID SIZE_POOL_COUNT
+# define SPECIAL_CONST_SHAPE_ID (SIZE_POOL_COUNT * 2)
 
 struct rb_shape {
     struct rb_id_table * edges; // id_table from ID (ivar) to next shape
@@ -63,6 +63,7 @@ enum shape_type {
     SHAPE_CAPACITY_CHANGE,
     SHAPE_IVAR_UNDEF,
     SHAPE_INITIAL_CAPACITY,
+    SHAPE_T_OBJECT,
 };
 
 #if SHAPE_IN_BASIC_FLAGS
@@ -131,6 +132,7 @@ static inline shape_id_t RCLASS_SHAPE_ID(VALUE obj) {
 
 bool rb_shape_root_shape_p(rb_shape_t* shape);
 rb_shape_t * rb_shape_get_root_shape(void);
+uint8_t rb_shape_id_num_bits(void);
 
 rb_shape_t* rb_shape_get_shape_by_id_without_assertion(shape_id_t shape_id);
 rb_shape_t * rb_shape_get_parent(rb_shape_t * shape);
diff --git a/signal.c b/signal.c
index 874afd28d5b3bc..04db34fc3dd6c3 100644
--- a/signal.c
+++ b/signal.c
@@ -1129,7 +1129,7 @@ rb_signal_exec(rb_thread_t *th, int sig)
             break;
         }
     }
-    else if (cmd == Qundef) {
+    else if (UNDEF_P(cmd)) {
         rb_threadptr_signal_exit(th);
     }
     else {
diff --git a/sprintf.c b/sprintf.c
index bfe25e1d3c8b05..b26dffec8570df 100644
--- a/sprintf.c
+++ b/sprintf.c
@@ -97,7 +97,7 @@ sign_bits(int base, const char *p)
     blen += (l);\
 } while (0)
 
-#define GETARG() (nextvalue != Qundef ? nextvalue : \
+#define GETARG() (!UNDEF_P(nextvalue) ? nextvalue : \
                   GETNEXTARG())
 
 #define GETNEXTARG() ( \
@@ -193,7 +193,7 @@ get_hash(volatile VALUE *hash, int argc, const VALUE *argv)
 {
     VALUE tmp;
 
-    if (*hash != Qundef) return *hash;
+    if (!UNDEF_P(*hash)) return *hash;
     if (argc != 2) {
         rb_raise(rb_eArgError, "one hash required");
     }
@@ -336,7 +336,7 @@ rb_str_format(int argc, const VALUE *argv, VALUE fmt)
             n = 0;
             GETNUM(n, width);
             if (*p == '$') {
-                if (nextvalue != Qundef) {
+                if (!UNDEF_P(nextvalue)) {
                     rb_raise(rb_eArgError, "value given twice - %d$", n);
                 }
                 nextvalue = GETPOSARG(n);
@@ -381,7 +381,7 @@ rb_str_format(int argc, const VALUE *argv, VALUE fmt)
                                            len - 2 /* without parenthesis */,
                                            enc);
                 if (!NIL_P(sym)) nextvalue = rb_hash_lookup2(hash, sym, Qundef);
-                if (nextvalue == Qundef) {
+                if (UNDEF_P(nextvalue)) {
                     if (NIL_P(sym)) {
                         sym = rb_sym_intern(start + 1,
                                             len - 2 /* without parenthesis */,
diff --git a/string.c b/string.c
index 1ce4a07651dcaf..990fe8f8273751 100644
--- a/string.c
+++ b/string.c
@@ -499,7 +499,7 @@ register_fstring(VALUE str, bool copy)
         do {
             args.fstr = str;
             st_update(frozen_strings, (st_data_t)str, fstr_update_callback, (st_data_t)&args);
-        } while (args.fstr == Qundef);
+        } while (UNDEF_P(args.fstr));
     }
     RB_VM_LOCK_LEAVE();
 
@@ -1877,10 +1877,10 @@ rb_str_init(int argc, VALUE *argv, VALUE str)
         rb_get_kwargs(opt, keyword_ids, 0, 2, kwargs);
         venc = kwargs[0];
         vcapa = kwargs[1];
-        if (venc != Qundef && !NIL_P(venc)) {
+        if (!UNDEF_P(venc) && !NIL_P(venc)) {
             enc = rb_to_encoding(venc);
         }
-        if (vcapa != Qundef && !NIL_P(vcapa)) {
+        if (!UNDEF_P(vcapa) && !NIL_P(vcapa)) {
             long capa = NUM2LONG(vcapa);
             long len = 0;
             int termlen = enc ? rb_enc_mbminlen(enc) : 1;
@@ -8926,7 +8926,7 @@ rb_str_enumerate_lines(int argc, VALUE *argv, VALUE str, VALUE ary)
             keywords[0] = rb_intern_const("chomp");
         }
         rb_get_kwargs(opts, keywords, 0, 1, &chomp);
-        chomp = (chomp != Qundef && RTEST(chomp));
+        chomp = (!UNDEF_P(chomp) && RTEST(chomp));
     }
 
     if (NIL_P(rs)) {
@@ -11528,23 +11528,6 @@ rb_sym_to_s(VALUE sym)
     return str_new_shared(rb_cString, rb_sym2str(sym));
 }
 
-/*
- *  call-seq:
- *    to_sym -> self
- *
- *  Returns +self+.
- *
- *  Symbol#intern is an alias for Symbol#to_sym.
- *
- *  Related: String#to_sym.
- */
-
-static VALUE
-sym_to_sym(VALUE sym)
-{
-    return sym;
-}
-
 MJIT_FUNC_EXPORTED VALUE
 rb_sym_proc_call(ID mid, int argc, const VALUE *argv, int kw_splat, VALUE passed_proc)
 {
@@ -12111,8 +12094,6 @@ Init_String(void)
     rb_define_method(rb_cSymbol, "to_s", rb_sym_to_s, 0);
     rb_define_method(rb_cSymbol, "id2name", rb_sym_to_s, 0);
     rb_define_method(rb_cSymbol, "name", rb_sym2str, 0); /* in symbol.c */
-    rb_define_method(rb_cSymbol, "intern", sym_to_sym, 0);
-    rb_define_method(rb_cSymbol, "to_sym", sym_to_sym, 0);
     rb_define_method(rb_cSymbol, "to_proc", rb_sym_to_proc, 0); /* in proc.c */
     rb_define_method(rb_cSymbol, "succ", sym_succ, 0);
     rb_define_method(rb_cSymbol, "next", sym_succ, 0);
diff --git a/struct.c b/struct.c
index da84fa6bcb7b76..10e5209fb989fd 100644
--- a/struct.c
+++ b/struct.c
@@ -650,7 +650,7 @@ rb_struct_s_def(int argc, VALUE *argv, VALUE klass)
             keyword_ids[0] = rb_intern("keyword_init");
         }
         rb_get_kwargs(opt, keyword_ids, 0, 1, &keyword_init);
-        if (keyword_init == Qundef) {
+        if (UNDEF_P(keyword_init)) {
             keyword_init = Qnil;
         }
         else if (RTEST(keyword_init)) {
diff --git a/symbol.c b/symbol.c
index adcc1275e3e30c..cd6a3c3407609c 100644
--- a/symbol.c
+++ b/symbol.c
@@ -22,6 +22,7 @@
 #include "ruby/st.h"
 #include "symbol.h"
 #include "vm_sync.h"
+#include "builtin.h"
 
 #ifndef USE_SYMBOL_GC
 # define USE_SYMBOL_GC 1
@@ -1262,3 +1263,4 @@ rb_is_local_name(VALUE name)
 }
 
 #include "id_table.c"
+#include "symbol.rbinc"
diff --git a/symbol.rb b/symbol.rb
new file mode 100644
index 00000000000000..0b23ebb267ea90
--- /dev/null
+++ b/symbol.rb
@@ -0,0 +1,15 @@
+class Symbol
+  # call-seq:
+  #   to_sym -> self
+  #
+  # Returns +self+.
+  #
+  # Symbol#intern is an alias for Symbol#to_sym.
+  #
+  # Related: String#to_sym.
+  def to_sym
+    self
+  end
+
+  alias intern to_sym
+end
diff --git a/test/fiber/test_enumerator.rb b/test/fiber/test_enumerator.rb
index c635f474dbde49..40f7d0172531dc 100644
--- a/test/fiber/test_enumerator.rb
+++ b/test/fiber/test_enumerator.rb
@@ -10,12 +10,6 @@ def test_read_characters
 
     i, o = UNIXSocket.pair
 
-    unless i.nonblock? && o.nonblock?
-      i.close
-      o.close
-      omit "I/O is not non-blocking!"
-    end
-
     message = String.new
 
     thread = Thread.new do
diff --git a/test/fiber/test_io.rb b/test/fiber/test_io.rb
index 821a169e44af72..de88745e57966c 100644
--- a/test/fiber/test_io.rb
+++ b/test/fiber/test_io.rb
@@ -6,14 +6,12 @@ class TestFiberIO < Test::Unit::TestCase
   MESSAGE = "Hello World"
 
   def test_read
-    omit "UNIXSocket is not defined!" unless defined?(UNIXSocket)
+    omit unless defined?(UNIXSocket)
 
     i, o = UNIXSocket.pair
-
-    unless i.nonblock? && o.nonblock?
-      i.close
-      o.close
-      omit "I/O is not non-blocking!"
+    if RUBY_PLATFORM=~/mswin|mingw/
+      i.nonblock = true
+      o.nonblock = true
     end
 
     message = nil
@@ -46,6 +44,10 @@ def test_heavy_read
     16.times.map do
       Thread.new do
         i, o = UNIXSocket.pair
+        if RUBY_PLATFORM=~/mswin|mingw/
+          i.nonblock = true
+          o.nonblock = true
+        end
 
         scheduler = Scheduler.new
         Fiber.set_scheduler scheduler
@@ -64,16 +66,11 @@ def test_heavy_read
   end
 
   def test_epipe_on_read
-    omit "UNIXSocket is not defined!" unless defined?(UNIXSocket)
+    omit unless defined?(UNIXSocket)
+    omit "nonblock=true isn't properly supported on Windows" if RUBY_PLATFORM=~/mswin|mingw/
 
     i, o = UNIXSocket.pair
 
-    unless i.nonblock? && o.nonblock?
-      i.close
-      o.close
-      omit "I/O is not non-blocking!"
-    end
-
     error = nil
 
     thread = Thread.new do
diff --git a/test/fileutils/test_fileutils.rb b/test/fileutils/test_fileutils.rb
index 05ba8d184ae307..2748bd247fe9b5 100644
--- a/test/fileutils/test_fileutils.rb
+++ b/test/fileutils/test_fileutils.rb
@@ -472,10 +472,14 @@ def test_cp_r_dev
   else
     def test_cp_r_socket
       pend "Skipping socket test on JRuby" if RUBY_ENGINE == 'jruby'
+
       Dir.mkdir('tmp/cpr_src')
       UNIXServer.new('tmp/cpr_src/socket').close
       cp_r 'tmp/cpr_src', 'tmp/cpr_dest'
       assert_equal(true, File.socket?('tmp/cpr_dest/socket'))
+    rescue Errno::EINVAL => error
+      # On some platforms (windows) sockets cannot be copied by FileUtils.
+      omit error.message
     end if defined?(UNIXServer)
   end
 
diff --git a/test/io/console/test_io_console.rb b/test/io/console/test_io_console.rb
index 3c44181f2ac0b6..27d8e4a9888d49 100644
--- a/test/io/console/test_io_console.rb
+++ b/test/io/console/test_io_console.rb
@@ -440,7 +440,9 @@ def helper
   def run_pty(src, n = 1)
     pend("PTY.spawn cannot control terminal on JRuby") if RUBY_ENGINE == 'jruby'
 
-    r, w, pid = PTY.spawn(EnvUtil.rubybin, "-I#{TestIO_Console::PATHS.join(File::PATH_SEPARATOR)}", "-rio/console", "-e", src)
+    args = ["-I#{TestIO_Console::PATHS.join(File::PATH_SEPARATOR)}", "-rio/console", "-e", src]
+    args.shift if args.first == "-I" # statically linked
+    r, w, pid = PTY.spawn(EnvUtil.rubybin, *args)
   rescue RuntimeError
     omit $!
   else
diff --git a/test/irb/helper.rb b/test/irb/helper.rb
index 15d5dafc57ef9d..293315879a1e8c 100644
--- a/test/irb/helper.rb
+++ b/test/irb/helper.rb
@@ -1,7 +1,37 @@
 require "test/unit"
 
+module IRB
+  class InputMethod; end
+end
+
 module TestIRB
   class TestCase < Test::Unit::TestCase
+    class TestInputMethod < ::IRB::InputMethod
+      attr_reader :list, :line_no
+
+      def initialize(list = [])
+        super("test")
+        @line_no = 0
+        @list = list
+      end
+
+      def gets
+        @list[@line_no]&.tap {@line_no += 1}
+      end
+
+      def eof?
+        @line_no >= @list.size
+      end
+
+      def encoding
+        Encoding.default_external
+      end
+
+      def reset
+        @line_no = 0
+      end
+    end
+
     def save_encodings
       @default_encoding = [Encoding.default_external, Encoding.default_internal]
       @stdio_encodings = [STDIN, STDOUT, STDERR].map {|io| [io.external_encoding, io.internal_encoding] }
diff --git a/test/irb/test_cmd.rb b/test/irb/test_cmd.rb
index 3af4ccec98dc02..bcfb1d0b86511b 100644
--- a/test/irb/test_cmd.rb
+++ b/test/irb/test_cmd.rb
@@ -6,32 +6,6 @@
 
 module TestIRB
   class ExtendCommandTest < TestCase
-    class TestInputMethod < ::IRB::InputMethod
-      attr_reader :list, :line_no
-
-      def initialize(list = [])
-        super("test")
-        @line_no = 0
-        @list = list
-      end
-
-      def gets
-        @list[@line_no]&.tap {@line_no += 1}
-      end
-
-      def eof?
-        @line_no >= @list.size
-      end
-
-      def encoding
-        Encoding.default_external
-      end
-
-      def reset
-        @line_no = 0
-      end
-    end
-
     def setup
       @pwd = Dir.pwd
       @tmpdir = File.join(Dir.tmpdir, "test_reline_config_#{$$}")
@@ -549,7 +523,7 @@ def test_show_source_end_finder
         def show_source_test_method
           unless true
           end
-        end
+        end unless defined?(show_source_test_method)
       EOS
 
       out, err = execute_lines(
diff --git a/test/irb/test_context.rb b/test/irb/test_context.rb
index e7cc0bab4f4fd8..4d256a73a20e4c 100644
--- a/test/irb/test_context.rb
+++ b/test/irb/test_context.rb
@@ -7,32 +7,6 @@
 
 module TestIRB
   class TestContext < TestCase
-    class TestInputMethod < ::IRB::InputMethod
-      attr_reader :list, :line_no
-
-      def initialize(list = [])
-        super("test")
-        @line_no = 0
-        @list = list
-      end
-
-      def gets
-        @list[@line_no]&.tap {@line_no += 1}
-      end
-
-      def eof?
-        @line_no >= @list.size
-      end
-
-      def encoding
-        Encoding.default_external
-      end
-
-      def reset
-        @line_no = 0
-      end
-    end
-
     def setup
       IRB.init_config(nil)
       IRB.conf[:USE_SINGLELINE] = false
@@ -518,7 +492,7 @@ def test_eval_input_with_exception
         irb.eval_input
       end
       assert_empty err
-      if '2.5.0' <= RUBY_VERSION && RUBY_VERSION < '3.0.0' && STDOUT.tty?
+      if RUBY_VERSION < '3.0.0' && STDOUT.tty?
         expected = [
           :*, /Traceback \(most recent call last\):\n/,
           :*, /\t 2: from \(irb\):1:in `<main>'\n/,
@@ -549,7 +523,7 @@ def test_eval_input_with_invalid_byte_sequence_exception
         irb.eval_input
       end
       assert_empty err
-      if '2.5.0' <= RUBY_VERSION && RUBY_VERSION < '3.0.0' && STDOUT.tty?
+      if RUBY_VERSION < '3.0.0' && STDOUT.tty?
         expected = [
           :*, /Traceback \(most recent call last\):\n/,
           :*, /\t 2: from \(irb\):1:in `<main>'\n/,
@@ -586,7 +560,7 @@ def test_eval_input_with_long_exception
         irb.eval_input
       end
       assert_empty err
-      if '2.5.0' <= RUBY_VERSION && RUBY_VERSION < '3.0.0' && STDOUT.tty?
+      if RUBY_VERSION < '3.0.0' && STDOUT.tty?
         expected = [
           :*, /Traceback \(most recent call last\):\n/,
           :*, /\t... \d+ levels...\n/,
diff --git a/test/irb/test_history.rb b/test/irb/test_history.rb
index b0a07ca29d3e8a..2ef4bb337351b6 100644
--- a/test/irb/test_history.rb
+++ b/test/irb/test_history.rb
@@ -15,38 +15,10 @@ def teardown
       IRB.conf[:RC_NAME_GENERATOR] = nil
     end
 
-    class TestInputMethod < ::IRB::InputMethod
+    class TestInputMethodWithHistory < TestInputMethod
       HISTORY = Array.new
 
       include IRB::HistorySavingAbility
-
-      attr_reader :list, :line_no
-
-      def initialize(list = [])
-        super("test")
-        @line_no = 0
-        @list = list
-      end
-
-      def gets
-        @list[@line_no]&.tap {@line_no += 1}
-      end
-
-      def eof?
-        @line_no >= @list.size
-      end
-
-      def encoding
-        Encoding.default_external
-      end
-
-      def reset
-        @line_no = 0
-      end
-
-      def winsize
-        [10, 20]
-      end
     end
 
     def test_history_save_1
@@ -167,7 +139,7 @@ def test_history_concurrent_use_not_present
       IRB.conf[:SAVE_HISTORY] = 1
       Dir.mktmpdir("test_irb_history_") do |tmpdir|
         ENV["HOME"] = tmpdir
-        io = TestInputMethod.new
+        io = TestInputMethodWithHistory.new
         io.class::HISTORY.clear
         io.load_history
         io.class::HISTORY.concat(%w"line1 line2")
@@ -198,7 +170,7 @@ def assert_history(expected_history, initial_irb_history, input)
           f.write(initial_irb_history)
         end
 
-        io = TestInputMethod.new
+        io = TestInputMethodWithHistory.new
         io.class::HISTORY.clear
         io.load_history
         if block_given?
diff --git a/test/irb/test_raise_no_backtrace_exception.rb b/test/irb/test_raise_no_backtrace_exception.rb
index ba8e89c59fb63b..9565419cdd0d64 100644
--- a/test/irb/test_raise_no_backtrace_exception.rb
+++ b/test/irb/test_raise_no_backtrace_exception.rb
@@ -1,4 +1,5 @@
 # frozen_string_literal: false
+require "tmpdir"
 
 require_relative "helper"
 
diff --git a/test/irb/test_ruby_lex.rb b/test/irb/test_ruby_lex.rb
index 2b16e2e9a10b6c..fa68a4632cb968 100644
--- a/test/irb/test_ruby_lex.rb
+++ b/test/irb/test_ruby_lex.rb
@@ -181,9 +181,6 @@ def test_symbols
     end
 
     def test_endless_range_at_end_of_line
-      if Gem::Version.new(RUBY_VERSION) < Gem::Version.new('2.6.0')
-        pend 'Endless range is available in 2.6.0 or later'
-      end
       input_with_prompt = [
         PromptRow.new('001:0: :> ', %q(a = 3..)),
         PromptRow.new('002:0: :* ', %q()),
diff --git a/test/lib/jit_support.rb b/test/lib/jit_support.rb
index 264fe9763e2a02..ce3ba6ba4b96b0 100644
--- a/test/lib/jit_support.rb
+++ b/test/lib/jit_support.rb
@@ -38,10 +38,10 @@ def eval_with_jit(env = nil, script, **opts)
     [stdout, stderr]
   end
 
-  def eval_with_jit_without_retry(env = nil, script, verbose: 0, min_calls: 5, save_temps: false, max_cache: 1000, wait: true, timeout: JIT_TIMEOUT)
+  def eval_with_jit_without_retry(env = nil, script, verbose: 0, call_threshold: 5, save_temps: false, max_cache: 1000, wait: true, timeout: JIT_TIMEOUT)
     args = [
       '--disable-gems', "--mjit-verbose=#{verbose}",
-      "--mjit-min-calls=#{min_calls}", "--mjit-max-cache=#{max_cache}",
+      "--mjit-call-threshold=#{call_threshold}", "--mjit-max-cache=#{max_cache}",
     ]
     args << '--disable-yjit'
     args << '--mjit-wait' if wait
diff --git a/test/ruby/test_ast.rb b/test/ruby/test_ast.rb
index 0932e93d5a909e..acf6722bb7391e 100644
--- a/test/ruby/test_ast.rb
+++ b/test/ruby/test_ast.rb
@@ -461,6 +461,30 @@ def test_until
     assert_not_equal(type1, type2)
   end
 
+  def test_rest_arg
+    rest_arg = lambda do |arg_str|
+      node = RubyVM::AbstractSyntaxTree.parse("def a(#{arg_str}) end")
+      node = node.children.last.children.last.children[1].children[-4]
+    end
+
+    assert_equal(nil, rest_arg.call(''))
+    assert_equal(:r, rest_arg.call('*r'))
+    assert_equal(:r, rest_arg.call('a, *r'))
+    assert_equal(:*, rest_arg.call('*'))
+    assert_equal(:*, rest_arg.call('a, *'))
+  end
+
+  def test_block_arg
+    block_arg = lambda do |arg_str|
+      node = RubyVM::AbstractSyntaxTree.parse("def a(#{arg_str}) end")
+      node = node.children.last.children.last.children[1].children[-1]
+    end
+
+    assert_equal(nil, block_arg.call(''))
+    assert_equal(:block, block_arg.call('&block'))
+    assert_equal(:&, block_arg.call('&'))
+  end
+
   def test_keyword_rest
     kwrest = lambda do |arg_str|
       node = RubyVM::AbstractSyntaxTree.parse("def a(#{arg_str}) end")
@@ -469,7 +493,7 @@ def test_keyword_rest
     end
 
     assert_equal(nil, kwrest.call(''))
-    assert_equal([nil], kwrest.call('**'))
+    assert_equal([:**], kwrest.call('**'))
     assert_equal(false, kwrest.call('**nil'))
     assert_equal([:a], kwrest.call('**a'))
   end
diff --git a/test/ruby/test_file_exhaustive.rb b/test/ruby/test_file_exhaustive.rb
index 8cd020533bd901..d0472a0081278b 100644
--- a/test/ruby/test_file_exhaustive.rb
+++ b/test/ruby/test_file_exhaustive.rb
@@ -649,7 +649,7 @@ def test_birthtime
       # ignore unsupporting filesystems
     rescue Errno::EPERM
       # Docker prohibits statx syscall by the default.
-      skip("statx(2) is prohibited by seccomp")
+      omit("statx(2) is prohibited by seccomp")
     end
     assert_raise(Errno::ENOENT) { File.birthtime(nofile) }
   end if File.respond_to?(:birthtime)
diff --git a/test/ruby/test_io.rb b/test/ruby/test_io.rb
index 6313e111791977..0bf24960c6ee92 100644
--- a/test/ruby/test_io.rb
+++ b/test/ruby/test_io.rb
@@ -900,6 +900,10 @@ def test_copy_stream_socket3
   end if defined? UNIXSocket
 
   def test_copy_stream_socket4
+    if RUBY_PLATFORM =~ /mingw|mswin/
+      omit "pread(2) is not implemented."
+    end
+
     with_bigsrc {|bigsrc, bigcontent|
       File.open(bigsrc) {|f|
         assert_equal(0, f.pos)
@@ -916,9 +920,13 @@ def test_copy_stream_socket4
         }
       }
     }
-  end if defined? UNIXSocket
+  end
 
   def test_copy_stream_socket5
+    if RUBY_PLATFORM =~ /mingw|mswin/
+      omit "pread(2) is not implemented."
+    end
+
     with_bigsrc {|bigsrc, bigcontent|
       File.open(bigsrc) {|f|
         assert_equal(bigcontent[0,100], f.read(100))
@@ -936,9 +944,13 @@ def test_copy_stream_socket5
         }
       }
     }
-  end if defined? UNIXSocket
+  end
 
   def test_copy_stream_socket6
+    if RUBY_PLATFORM =~ /mingw|mswin/
+      omit "pread(2) is not implemented."
+    end
+
     mkcdtmpdir {
       megacontent = "abc" * 1234567
       File.open("megasrc", "w") {|f| f << megacontent }
@@ -959,9 +971,13 @@ def test_copy_stream_socket6
         assert_equal(megacontent, result)
       }
     }
-  end if defined? UNIXSocket
+  end
 
   def test_copy_stream_socket7
+    if RUBY_PLATFORM =~ /mingw|mswin/
+      omit "pread(2) is not implemented."
+    end
+
     GC.start
     mkcdtmpdir {
       megacontent = "abc" * 1234567
@@ -996,7 +1012,7 @@ def test_copy_stream_socket7
         end
       }
     }
-  end if defined? UNIXSocket and IO.method_defined?("nonblock=")
+  end
 
   def test_copy_stream_strio
     src = StringIO.new("abcd")
diff --git a/test/ruby/test_io_timeout.rb b/test/ruby/test_io_timeout.rb
index ca4c0b833b5b63..e017395980564b 100644
--- a/test/ruby/test_io_timeout.rb
+++ b/test/ruby/test_io_timeout.rb
@@ -9,12 +9,6 @@ def with_pipe
     begin
       i, o = UNIXSocket.pair
 
-      unless i.nonblock? && o.nonblock?
-        i.close
-        o.close
-        omit "I/O is not non-blocking!"
-      end
-
       yield i, o
     ensure
       i.close
diff --git a/test/ruby/test_mjit.rb b/test/ruby/test_mjit.rb
index 2fc878154be639..2ed6d6ac091458 100644
--- a/test/ruby/test_mjit.rb
+++ b/test/ruby/test_mjit.rb
@@ -142,7 +142,7 @@ def test_compile_insn_instancevariable
     end;
 
     # optimized getinstancevariable call
-    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", stdout: '33', success_count: 1, min_calls: 2)
+    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", stdout: '33', success_count: 1, call_threshold: 2)
     begin;
       class A
         def initialize
@@ -533,7 +533,7 @@ def test_compile_insn_opt_or
 
   def test_compile_insn_opt_aref
     # optimized call (optimized JIT) -> send call
-    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", stdout: '21', success_count: 2, min_calls: 1, insns: %i[opt_aref])
+    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", stdout: '21', success_count: 2, call_threshold: 1, insns: %i[opt_aref])
     begin;
       obj = Object.new
       def obj.[](h)
@@ -546,7 +546,7 @@ def obj.[](h)
     end;
 
     # send call -> optimized call (send JIT) -> optimized call
-    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", stdout: '122', success_count: 2, min_calls: 2)
+    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", stdout: '122', success_count: 2, call_threshold: 2)
     begin;
       obj = Object.new
       def obj.[](h)
@@ -637,7 +637,7 @@ def test(arg = 'hello')
   end
 
   def test_mjit_output
-    out, err = eval_with_jit('5.times { puts "MJIT" }', verbose: 1, min_calls: 5)
+    out, err = eval_with_jit('5.times { puts "MJIT" }', verbose: 1, call_threshold: 5)
     assert_equal("MJIT\n" * 5, out)
     assert_match(/^#{JIT_SUCCESS_PREFIX}: block in <main>@-e:1 -> .+_ruby_mjit_p\d+u\d+\.c$/, err)
     assert_match(/^Successful MJIT finish$/, err)
@@ -686,7 +686,7 @@ def a11() print('hello') end
   def test_unload_units_and_compaction
     Dir.mktmpdir("jit_test_unload_units_") do |dir|
       # MIN_CACHE_SIZE is 10
-      out, err = eval_with_jit({"TMPDIR"=>dir}, "#{<<~"begin;"}\n#{<<~'end;'}", verbose: 1, min_calls: 1, max_cache: 10)
+      out, err = eval_with_jit({"TMPDIR"=>dir}, "#{<<~"begin;"}\n#{<<~'end;'}", verbose: 1, call_threshold: 1, max_cache: 10)
       begin;
         i = 0
         while i < 11
@@ -805,7 +805,7 @@ def wrapper(paths, prefixes)
   end
 
   def test_inlined_builtin_methods
-    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", stdout: '', success_count: 1, min_calls: 2)
+    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", stdout: '', success_count: 1, call_threshold: 2)
     begin;
       def test
         float = 0.0
@@ -819,7 +819,7 @@ def test
   end
 
   def test_inlined_c_method
-    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", stdout: "aaa", success_count: 2, recompile_count: 1, min_calls: 2)
+    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", stdout: "aaa", success_count: 2, recompile_count: 1, call_threshold: 2)
     begin;
       def test(obj, recursive: nil)
         if recursive
@@ -837,7 +837,7 @@ def test(obj, recursive: nil)
   end
 
   def test_inlined_exivar
-    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", stdout: "aaa", success_count: 4, recompile_count: 2, min_calls: 2)
+    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", stdout: "aaa", success_count: 4, recompile_count: 2, call_threshold: 2)
     begin;
       class Foo < Hash
         def initialize
@@ -856,7 +856,7 @@ def bar
   end
 
   def test_inlined_undefined_ivar
-    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", stdout: "bbb", success_count: 2, min_calls: 2)
+    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", stdout: "bbb", success_count: 2, call_threshold: 2)
     begin;
       class Foo
         def initialize
@@ -877,7 +877,7 @@ def bar
   end
 
   def test_inlined_setivar_frozen
-    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", stdout: "FrozenError\n", success_count: 2, min_calls: 3)
+    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", stdout: "FrozenError\n", success_count: 2, call_threshold: 3)
     begin;
       class A
         def a
@@ -899,7 +899,7 @@ def a
   end
 
   def test_inlined_getconstant
-    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", stdout: '11', success_count: 1, min_calls: 2)
+    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", stdout: '11', success_count: 1, call_threshold: 2)
     begin;
       FOO = 1
       def const
@@ -911,7 +911,7 @@ def const
   end
 
   def test_attr_reader
-    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", stdout: "4nil\nnil\n6", success_count: 2, min_calls: 2)
+    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", stdout: "4nil\nnil\n6", success_count: 2, call_threshold: 2)
     begin;
       class A
         attr_reader :a, :b
@@ -942,7 +942,7 @@ def a.test
       print(2 * a.test)
     end;
 
-    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", stdout: "true", success_count: 1, min_calls: 2)
+    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", stdout: "true", success_count: 1, call_threshold: 2)
     begin;
       class Hoge
         attr_reader :foo
@@ -977,7 +977,7 @@ def test(recv)
   def test_heap_promotion_of_ivar_in_the_middle_of_jit
     omit if GC.using_rvargc?
 
-    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", stdout: "true\ntrue\n", success_count: 2, min_calls: 2)
+    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", stdout: "true\ntrue\n", success_count: 2, call_threshold: 2)
     begin;
       class A
         def initialize
@@ -1004,7 +1004,7 @@ def add_ivar
   end
 
   def test_jump_to_precompiled_branch
-    assert_eval_with_jit("#{<<~'begin;'}\n#{<<~'end;'}", stdout: ".0", success_count: 1, min_calls: 1)
+    assert_eval_with_jit("#{<<~'begin;'}\n#{<<~'end;'}", stdout: ".0", success_count: 1, call_threshold: 1)
     begin;
       def test(foo)
         ".#{foo unless foo == 1}" if true
@@ -1038,7 +1038,7 @@ def test_clean_objects_on_exec
       omit '.bundle.dSYM directory is left but removing it is not supported for now'
     end
     Dir.mktmpdir("jit_test_clean_objects_on_exec_") do |dir|
-      eval_with_jit({"TMPDIR"=>dir}, "#{<<~"begin;"}\n#{<<~"end;"}", min_calls: 1)
+      eval_with_jit({"TMPDIR"=>dir}, "#{<<~"begin;"}\n#{<<~"end;"}", call_threshold: 1)
       begin;
         def a; end; a
         exec "true"
@@ -1070,7 +1070,7 @@ def test_stack_pointer_with_assignment
   end
 
   def test_frame_omitted_inlining
-    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", stdout: "true\ntrue\ntrue\n", success_count: 1, min_calls: 2)
+    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", stdout: "true\ntrue\ntrue\n", success_count: 1, call_threshold: 2)
     begin;
       class Integer
         remove_method :zero?
@@ -1086,7 +1086,7 @@ def zero?
   end
 
   def test_block_handler_with_possible_frame_omitted_inlining
-    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", stdout: "70.0\n70.0\n70.0\n", success_count: 2, min_calls: 2)
+    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", stdout: "70.0\n70.0\n70.0\n", success_count: 2, call_threshold: 2)
     begin;
       def multiply(a, b)
         a *= b
@@ -1099,7 +1099,7 @@ def multiply(a, b)
   end
 
   def test_builtin_frame_omitted_inlining
-    assert_eval_with_jit('0.zero?; 0.zero?; 3.times { p 0.zero? }', stdout: "true\ntrue\ntrue\n", success_count: 1, min_calls: 2)
+    assert_eval_with_jit('0.zero?; 0.zero?; 3.times { p 0.zero? }', stdout: "true\ntrue\ntrue\n", success_count: 1, call_threshold: 2)
   end
 
   def test_program_counter_with_regexpmatch
@@ -1131,7 +1131,7 @@ def test_pushed_values_with_opt_aref_with
   end
 
   def test_mjit_pause_wait
-    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", stdout: '', success_count: 0, min_calls: 1)
+    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", stdout: '', success_count: 0, call_threshold: 1)
     begin;
       RubyVM::MJIT.pause
       proc {}.call
@@ -1139,7 +1139,7 @@ def test_mjit_pause_wait
   end
 
   def test_not_cancel_by_tracepoint_class
-    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", success_count: 1, min_calls: 2)
+    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", success_count: 1, call_threshold: 2)
     begin;
       TracePoint.new(:class) {}.enable
       2.times {}
@@ -1147,7 +1147,7 @@ def test_not_cancel_by_tracepoint_class
   end
 
   def test_cancel_by_tracepoint
-    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", success_count: 0, min_calls: 2)
+    assert_eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", success_count: 0, call_threshold: 2)
     begin;
       TracePoint.new(:line) {}.enable
       2.times {}
@@ -1155,7 +1155,7 @@ def test_cancel_by_tracepoint
   end
 
   def test_caller_locations_without_catch_table
-    out, _ = eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", min_calls: 1)
+    out, _ = eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", call_threshold: 1)
     begin;
       def b                             # 2
         caller_locations.first          # 3
@@ -1175,8 +1175,8 @@ def a                             # 6
 
   def test_fork_with_mjit_worker_thread
     Dir.mktmpdir("jit_test_fork_with_mjit_worker_thread_") do |dir|
-      # min_calls: 2 to skip fork block
-      out, err = eval_with_jit({ "TMPDIR" => dir }, "#{<<~"begin;"}\n#{<<~"end;"}", min_calls: 2, verbose: 1)
+      # call_threshold: 2 to skip fork block
+      out, err = eval_with_jit({ "TMPDIR" => dir }, "#{<<~"begin;"}\n#{<<~"end;"}", call_threshold: 2, verbose: 1)
       begin;
         def before_fork; end
         def after_fork; end
@@ -1206,7 +1206,7 @@ def after_fork; end
   end if defined?(fork)
 
   def test_jit_failure
-    _, err = eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", min_calls: 1, verbose: 1)
+    _, err = eval_with_jit("#{<<~"begin;"}\n#{<<~"end;"}", call_threshold: 1, verbose: 1)
     begin;
       1.times do
         class A
@@ -1230,14 +1230,14 @@ def assert_compile_once(script, result_inspect:, insns: [], uplevel: 1)
   end
 
   # Shorthand for normal test cases
-  def assert_eval_with_jit(script, stdout: nil, success_count:, recompile_count: nil, min_calls: 1, max_cache: 1000, insns: [], uplevel: 1, ignorable_patterns: [])
-    out, err = eval_with_jit(script, verbose: 1, min_calls: min_calls, max_cache: max_cache)
+  def assert_eval_with_jit(script, stdout: nil, success_count:, recompile_count: nil, call_threshold: 1, max_cache: 1000, insns: [], uplevel: 1, ignorable_patterns: [])
+    out, err = eval_with_jit(script, verbose: 1, call_threshold: call_threshold, max_cache: max_cache)
     success_actual = err.scan(/^#{JIT_SUCCESS_PREFIX}:/).size
     recompile_actual = err.scan(/^#{JIT_RECOMPILE_PREFIX}:/).size
     # Add --mjit-verbose=2 logs for cl.exe because compiler's error message is suppressed
     # for cl.exe with --mjit-verbose=1. See `start_process` in mjit.c.
     if RUBY_PLATFORM.match?(/mswin/) && success_count != success_actual
-      out2, err2 = eval_with_jit(script, verbose: 2, min_calls: min_calls, max_cache: max_cache)
+      out2, err2 = eval_with_jit(script, verbose: 2, call_threshold: call_threshold, max_cache: max_cache)
     end
 
     # Make sure that the script has insns expected to be tested
diff --git a/test/ruby/test_rubyoptions.rb b/test/ruby/test_rubyoptions.rb
index 0198bbd9003e9f..15c9f293ede616 100644
--- a/test/ruby/test_rubyoptions.rb
+++ b/test/ruby/test_rubyoptions.rb
@@ -14,7 +14,7 @@ def self.yjit_enabled? = defined?(RubyVM::YJIT.enabled?) && RubyVM::YJIT.enabled
     if mjit_enabled?
       RUBY_DESCRIPTION.sub(/\+MJIT /, '')
     elsif yjit_enabled?
-      RUBY_DESCRIPTION.sub(/\+YJIT /, '')
+      RUBY_DESCRIPTION.sub(/\+YJIT( (dev|dev_nodebug|stats))? /, '')
     else
       RUBY_DESCRIPTION
     end
diff --git a/test/ruby/test_rubyvm_mjit.rb b/test/ruby/test_rubyvm_mjit.rb
index 8ca0fb9ef22cf1..90ff2edc8ef509 100644
--- a/test/ruby/test_rubyvm_mjit.rb
+++ b/test/ruby/test_rubyvm_mjit.rb
@@ -14,7 +14,7 @@ def setup
   end
 
   def test_pause
-    out, err = eval_with_jit(<<~'EOS', verbose: 1, min_calls: 1, wait: false)
+    out, err = eval_with_jit(<<~'EOS', verbose: 1, call_threshold: 1, wait: false)
       i = 0
       while i < 5
         eval("def mjit#{i}; end; mjit#{i}")
@@ -36,7 +36,7 @@ def test_pause
   end
 
   def test_pause_waits_until_compaction
-    out, err = eval_with_jit(<<~'EOS', verbose: 1, min_calls: 1, wait: false)
+    out, err = eval_with_jit(<<~'EOS', verbose: 1, call_threshold: 1, wait: false)
       def a() end; a
       def b() end; b
       RubyVM::MJIT.pause
@@ -52,7 +52,7 @@ def b() end; b
   end
 
   def test_pause_after_waitall
-    out, err = eval_with_jit(<<~'EOS', verbose: 1, min_calls: 1, wait: false)
+    out, err = eval_with_jit(<<~'EOS', verbose: 1, call_threshold: 1, wait: false)
       def test() = nil
       test
       Process.waitall
@@ -65,7 +65,7 @@ def test() = nil
   end
 
   def test_pause_does_not_hang_on_full_units
-    out, _ = eval_with_jit(<<~'EOS', verbose: 1, min_calls: 1, max_cache: 10, wait: false)
+    out, _ = eval_with_jit(<<~'EOS', verbose: 1, call_threshold: 1, max_cache: 10, wait: false)
       i = 0
       while i < 11
         eval("def mjit#{i}; end; mjit#{i}")
@@ -77,7 +77,7 @@ def test_pause_does_not_hang_on_full_units
   end
 
   def test_pause_wait_false
-    out, err = eval_with_jit(<<~'EOS', verbose: 1, min_calls: 1, wait: false)
+    out, err = eval_with_jit(<<~'EOS', verbose: 1, call_threshold: 1, wait: false)
       i = 0
       while i < 10
         eval("def mjit#{i}; end; mjit#{i}")
@@ -95,7 +95,7 @@ def test_pause_wait_false
   end
 
   def test_resume
-    out, err = eval_with_jit(<<~'EOS', verbose: 1, min_calls: 1, wait: false)
+    out, err = eval_with_jit(<<~'EOS', verbose: 1, call_threshold: 1, wait: false)
       print RubyVM::MJIT.resume
       print RubyVM::MJIT.pause
       print RubyVM::MJIT.resume
diff --git a/test/ruby/test_shapes.rb b/test/ruby/test_shapes.rb
index 326ff3a4537391..848bb4971aadb4 100644
--- a/test/ruby/test_shapes.rb
+++ b/test/ruby/test_shapes.rb
@@ -88,8 +88,8 @@ def test_iv_index
 
   class TestObject; end
 
-  def test_new_obj_has_root_shape
-    assert_shape_equal(RubyVM::Shape.root_shape, RubyVM::Shape.of(TestObject.new))
+  def test_new_obj_has_t_object_shape
+    assert_shape_equal(RubyVM::Shape.root_shape, RubyVM::Shape.of(TestObject.new).parent)
   end
 
   def test_str_has_root_shape
@@ -114,14 +114,23 @@ def test_nil_has_special_const_shape_id
 
   def test_basic_shape_transition
     obj = Example.new
-    refute_equal(RubyVM::Shape.root_shape, RubyVM::Shape.of(obj))
-    assert_shape_equal(RubyVM::Shape.root_shape.edges[:@a], RubyVM::Shape.of(obj))
+    shape = RubyVM::Shape.of(obj)
+    refute_equal(RubyVM::Shape.root_shape, shape)
+    assert_equal :@a, shape.edge_name
+    assert_equal RubyVM::Shape::SHAPE_IVAR, shape.type
+
+    shape = shape.parent
+    assert_equal RubyVM::Shape::SHAPE_T_OBJECT, shape.type
+
+    shape = shape.parent
+    assert_equal(RubyVM::Shape.root_shape.id, shape.id)
     assert_equal(obj.instance_variable_get(:@a), 1)
   end
 
   def test_different_objects_make_same_transition
-    obj = Example.new
+    obj = []
     obj2 = ""
+    obj.instance_variable_set(:@a, 1)
     obj2.instance_variable_set(:@a, 1)
     assert_shape_equal(RubyVM::Shape.of(obj), RubyVM::Shape.of(obj2))
   end
diff --git a/test/ruby/test_syntax.rb b/test/ruby/test_syntax.rb
index b0ad012131208c..251448ec011615 100644
--- a/test/ruby/test_syntax.rb
+++ b/test/ruby/test_syntax.rb
@@ -163,9 +163,11 @@ def b(**); c(**) end
         def c(**kw); kw end
         def d(**); b(k: 1, **) end
         def e(**); b(**, k: 1) end
+        def f(a: nil, **); b(**) end
         assert_equal({a: 1, k: 3}, b(a: 1, k: 3))
         assert_equal({a: 1, k: 3}, d(a: 1, k: 3))
         assert_equal({a: 1, k: 1}, e(a: 1, k: 3))
+        assert_equal({k: 3}, f(a: 1, k: 3))
     end;
   end
 
@@ -1707,6 +1709,8 @@ def test_argument_forwarding
     assert_syntax_error('def foo(...) foo[...] = x; end', /unexpected/)
     assert_syntax_error('def foo(...) foo(...) { }; end', /both block arg and actual block given/)
     assert_syntax_error('def foo(...) defined?(...); end', /unexpected/)
+    assert_syntax_error('def foo(*rest, ...) end', '... after rest argument')
+    assert_syntax_error('def foo(*, ...) end', '... after rest argument')
 
     obj1 = Object.new
     def obj1.bar(*args, **kws, &block)
diff --git a/test/ruby/test_yjit.rb b/test/ruby/test_yjit.rb
index fab8768a7e4692..9ab058d97bb2dd 100644
--- a/test/ruby/test_yjit.rb
+++ b/test/ruby/test_yjit.rb
@@ -905,7 +905,7 @@ def test_code_gc_with_many_iseqs
         end
       }
 
-      return :not_paged1 unless add_pages(500) # use some pages
+      return :not_paged1 unless add_pages(250) # use some pages
       return :broken_resume1 if fiber.resume != 0 # leave an on-stack code as well
 
       add_pages(2000) # use a whole lot of pages to run out of 1MiB
diff --git a/test/socket/test_nonblock.rb b/test/socket/test_nonblock.rb
index d9d1e186b2c518..5a4688bac3421a 100644
--- a/test/socket/test_nonblock.rb
+++ b/test/socket/test_nonblock.rb
@@ -307,11 +307,13 @@ def test_sendmsg_nonblock_seqpacket
           loop { s1.sendmsg_nonblock(buf) }
         end
       end
-    rescue NotImplementedError, Errno::ENOSYS, Errno::EPROTONOSUPPORT
+    rescue NotImplementedError, Errno::ENOSYS, Errno::EPROTONOSUPPORT, Errno::EPROTOTYPE
       omit "UNIXSocket.pair(:SEQPACKET) not implemented on this platform: #{$!}"
     end
 
     def test_sendmsg_nonblock_no_exception
+      omit "AF_UNIX + SEQPACKET is not supported on windows" if /mswin|mingw/ =~ RUBY_PLATFORM
+
       buf = '*' * 4096
       UNIXSocket.pair(:SEQPACKET) do |s1, s2|
         n = 0
diff --git a/test/socket/test_unix.rb b/test/socket/test_unix.rb
index 8c74d0c93989ea..e206339db09596 100644
--- a/test/socket/test_unix.rb
+++ b/test/socket/test_unix.rb
@@ -60,6 +60,8 @@ def test_fd_passing_class_mode
       assert_not_equal s1.fileno, r.fileno
       r.close
     end
+  rescue NotImplementedError => error
+    omit error.message
   end
 
   def test_fd_passing_n
@@ -334,62 +336,70 @@ def test_cloexec
   end
 
   def test_noname_path
-    s1, s2 = UNIXSocket.pair
-    assert_equal("", s1.path)
-    assert_equal("", s2.path)
-  ensure
-    s1.close
-    s2.close
+    if /mswin|mingw/ =~ RUBY_PLATFORM
+      omit "unnamed pipe is emulated on windows"
+    end
+
+    UNIXSocket.pair do |s1, s2|
+      assert_equal("", s1.path)
+      assert_equal("", s2.path)
+    end
   end
 
   def test_noname_addr
-    s1, s2 = UNIXSocket.pair
-    assert_equal(["AF_UNIX", ""], s1.addr)
-    assert_equal(["AF_UNIX", ""], s2.addr)
-  ensure
-    s1.close
-    s2.close
+    if /mswin|mingw/ =~ RUBY_PLATFORM
+      omit "unnamed pipe is emulated on windows"
+    end
+
+    UNIXSocket.pair do |s1, s2|
+      assert_equal(["AF_UNIX", ""], s1.addr)
+      assert_equal(["AF_UNIX", ""], s2.addr)
+    end
   end
 
   def test_noname_peeraddr
-    s1, s2 = UNIXSocket.pair
-    assert_equal(["AF_UNIX", ""], s1.peeraddr)
-    assert_equal(["AF_UNIX", ""], s2.peeraddr)
-  ensure
-    s1.close
-    s2.close
+    if /mswin|mingw/ =~ RUBY_PLATFORM
+      omit "unnamed pipe is emulated on windows"
+    end
+
+    UNIXSocket.pair do |s1, s2|
+      assert_equal(["AF_UNIX", ""], s1.peeraddr)
+      assert_equal(["AF_UNIX", ""], s2.peeraddr)
+    end
   end
 
   def test_noname_unpack_sockaddr_un
-    s1, s2 = UNIXSocket.pair
-    n = nil
-    assert_equal("", Socket.unpack_sockaddr_un(n)) if (n = s1.getsockname) != ""
-    assert_equal("", Socket.unpack_sockaddr_un(n)) if (n = s1.getsockname) != ""
-    assert_equal("", Socket.unpack_sockaddr_un(n)) if (n = s2.getsockname) != ""
-    assert_equal("", Socket.unpack_sockaddr_un(n)) if (n = s1.getpeername) != ""
-    assert_equal("", Socket.unpack_sockaddr_un(n)) if (n = s2.getpeername) != ""
-  ensure
-    s1.close
-    s2.close
+    if /mswin|mingw/ =~ RUBY_PLATFORM
+      omit "unnamed pipe is emulated on windows"
+    end
+
+    UNIXSocket.pair do |s1, s2|
+      n = nil
+      assert_equal("", Socket.unpack_sockaddr_un(n)) if (n = s1.getsockname) != ""
+      assert_equal("", Socket.unpack_sockaddr_un(n)) if (n = s1.getsockname) != ""
+      assert_equal("", Socket.unpack_sockaddr_un(n)) if (n = s2.getsockname) != ""
+      assert_equal("", Socket.unpack_sockaddr_un(n)) if (n = s1.getpeername) != ""
+      assert_equal("", Socket.unpack_sockaddr_un(n)) if (n = s2.getpeername) != ""
+    end
   end
 
   def test_noname_recvfrom
-    s1, s2 = UNIXSocket.pair
-    s2.write("a")
-    assert_equal(["a", ["AF_UNIX", ""]], s1.recvfrom(10))
-  ensure
-    s1.close
-    s2.close
+    if /mswin|mingw/ =~ RUBY_PLATFORM
+      omit "unnamed pipe is emulated on windows"
+    end
+
+    UNIXSocket.pair do |s1, s2|
+      s2.write("a")
+      assert_equal(["a", ["AF_UNIX", ""]], s1.recvfrom(10))
+    end
   end
 
   def test_noname_recv_nonblock
-    s1, s2 = UNIXSocket.pair
-    s2.write("a")
-    IO.select [s1]
-    assert_equal("a", s1.recv_nonblock(10))
-  ensure
-    s1.close
-    s2.close
+    UNIXSocket.pair do |s1, s2|
+      s2.write("a")
+      IO.select [s1]
+      assert_equal("a", s1.recv_nonblock(10))
+    end
   end
 
   def test_too_long_path
@@ -429,12 +439,18 @@ def test_dgram_pair
     rv = s1.recv(100, 0, buf)
     assert_equal buf.object_id, rv.object_id
     assert_equal "BBBBBB", rv
+  rescue Errno::EPROTOTYPE => error
+    omit error.message
   ensure
     s1.close if s1
     s2.close if s2
   end
 
   def test_dgram_pair_sendrecvmsg_errno_set
+    if /mswin|mingw/ =~ RUBY_PLATFORM
+      omit("AF_UNIX + SOCK_DGRAM is not supported on windows")
+    end
+
     s1, s2 = to_close = UNIXSocket.pair(Socket::SOCK_DGRAM)
     pipe = IO.pipe
     to_close.concat(pipe)
@@ -457,9 +473,17 @@ def test_dgram_pair_sendrecvmsg_errno_set
   end
 
   def test_epipe # [ruby-dev:34619]
+    # This is a good example of why reporting the exact `errno` is a terrible
+    # idea for platform abstractions.
+    if RUBY_PLATFORM =~ /mswin|mingw/
+      error = Errno::ESHUTDOWN
+    else
+      error = Errno::EPIPE
+    end
+
     UNIXSocket.pair {|s1, s2|
       s1.shutdown(Socket::SHUT_WR)
-      assert_raise(Errno::EPIPE) { s1.write "a" }
+      assert_raise(error) { s1.write "a" }
       assert_equal(nil, s2.read(1))
       s2.write "a"
       assert_equal("a", s1.read(1))
@@ -493,6 +517,45 @@ def test_unix_socket_pair_close_on_exec
     }
   end
 
+  if /mingw|mswin/ =~ RUBY_PLATFORM
+
+    def test_unix_socket_with_encoding
+      Dir.mktmpdir do |tmpdir|
+        path = "#{tmpdir}/sockäöü".encode("cp850")
+        UNIXServer.open(path) do |serv|
+          assert File.socket?(path)
+          assert File.stat(path).socket?
+          assert File.lstat(path).socket?
+          assert_equal path.encode("utf-8"), serv.path
+          UNIXSocket.open(path) do |s1|
+            s2 = serv.accept
+            s2.close
+          end
+        end
+      end
+    end
+
+    def test_windows_unix_socket_pair_with_umlaut
+      otmp = ENV['TMP']
+      ENV['TMP'] = File.join(Dir.tmpdir, "äöü€")
+      FileUtils.mkdir_p ENV['TMP']
+
+      s1, = UNIXSocket.pair
+      assert !s1.path.empty?
+      assert !File.exist?(s1.path)
+    ensure
+      FileUtils.rm_rf ENV['TMP']
+      ENV['TMP'] = otmp
+    end
+
+    def test_windows_unix_socket_pair_paths
+      s1, s2 = UNIXSocket.pair
+      assert !s1.path.empty?
+      assert s2.path.empty?
+      assert !File.exist?(s1.path)
+    end
+  end
+
   def test_initialize
     Dir.mktmpdir {|d|
       Socket.open(Socket::AF_UNIX, Socket::SOCK_STREAM, 0) {|s|
diff --git a/thread.c b/thread.c
index 89d4a910c14fa0..6e45b4d3154947 100644
--- a/thread.c
+++ b/thread.c
@@ -692,7 +692,7 @@ thread_start_func_2(rb_thread_t *th, VALUE *stack_start)
     th->ec->machine.stack_maxsize -= size * sizeof(VALUE);
 
     // Ensure that we are not joinable.
-    VM_ASSERT(th->value == Qundef);
+    VM_ASSERT(UNDEF_P(th->value));
 
     EC_PUSH_TAG(th->ec);
 
@@ -738,7 +738,7 @@ thread_start_func_2(rb_thread_t *th, VALUE *stack_start)
     }
 
     // The thread is effectively finished and can be joined.
-    VM_ASSERT(th->value != Qundef);
+    VM_ASSERT(!UNDEF_P(th->value));
 
     rb_threadptr_join_list_wakeup(th);
     rb_threadptr_unlock_all_locking_mutexes(th);
@@ -1038,7 +1038,7 @@ remove_from_join_list(VALUE arg)
 static int
 thread_finished(rb_thread_t *th)
 {
-    return th->status == THREAD_KILLED || th->value != Qundef;
+    return th->status == THREAD_KILLED || !UNDEF_P(th->value);
 }
 
 static VALUE
@@ -1230,7 +1230,7 @@ thread_value(VALUE self)
 {
     rb_thread_t *th = rb_thread_ptr(self);
     thread_join(th, Qnil, 0);
-    if (th->value == Qundef) {
+    if (UNDEF_P(th->value)) {
         // If the thread is dead because we forked th->value is still Qundef.
         return Qnil;
     }
@@ -2360,7 +2360,7 @@ rb_threadptr_execute_interrupts(rb_thread_t *th, int blocking_timing)
             RUBY_DEBUG_LOG("err:%"PRIdVALUE"\n", err);
             ret = TRUE;
 
-            if (err == Qundef) {
+            if (UNDEF_P(err)) {
                 /* no error */
             }
             else if (err == eKillSignal        /* Thread#kill received */   ||
@@ -5046,7 +5046,7 @@ recursive_check(VALUE list, VALUE obj, VALUE paired_obj_id)
 #endif
 
     VALUE pair_list = rb_hash_lookup2(list, obj, Qundef);
-    if (pair_list == Qundef)
+    if (UNDEF_P(pair_list))
         return Qfalse;
     if (paired_obj_id) {
         if (!RB_TYPE_P(pair_list, T_HASH)) {
@@ -5078,7 +5078,7 @@ recursive_push(VALUE list, VALUE obj, VALUE paired_obj)
     if (!paired_obj) {
         rb_hash_aset(list, obj, Qtrue);
     }
-    else if ((pair_list = rb_hash_lookup2(list, obj, Qundef)) == Qundef) {
+    else if (UNDEF_P(pair_list = rb_hash_lookup2(list, obj, Qundef))) {
         rb_hash_aset(list, obj, paired_obj);
     }
     else {
@@ -5105,7 +5105,7 @@ recursive_pop(VALUE list, VALUE obj, VALUE paired_obj)
 {
     if (paired_obj) {
         VALUE pair_list = rb_hash_lookup2(list, obj, Qundef);
-        if (pair_list == Qundef) {
+        if (UNDEF_P(pair_list)) {
             return 0;
         }
         if (RB_TYPE_P(pair_list, T_HASH)) {
diff --git a/time.c b/time.c
index fe4ea0014465ca..7d74b56a3be451 100644
--- a/time.c
+++ b/time.c
@@ -523,7 +523,7 @@ num_exact(VALUE v)
         return rb_rational_canonicalize(v);
 
       default:
-        if ((tmp = rb_check_funcall(v, idTo_r, 0, NULL)) != Qundef) {
+        if (!UNDEF_P(tmp = rb_check_funcall(v, idTo_r, 0, NULL))) {
             /* test to_int method availability to reject non-Numeric
              * objects such as String, Time, etc which have to_r method. */
             if (!rb_respond_to(v, idTo_int)) {
@@ -2277,7 +2277,7 @@ zone_set_dst(VALUE zone, struct time_object *tobj, VALUE tm)
     VALUE dst;
     CONST_ID(id_dst_p, "dst?");
     dst = rb_check_funcall(zone, id_dst_p, 1, &tm);
-    tobj->vtm.isdst = (dst != Qundef && RTEST(dst));
+    tobj->vtm.isdst = (!UNDEF_P(dst) && RTEST(dst));
 }
 
 static int
@@ -2290,7 +2290,7 @@ zone_timelocal(VALUE zone, VALUE time)
     t = rb_time_unmagnify(tobj->timew);
     tm = tm_from_time(rb_cTimeTM, time);
     utc = rb_check_funcall(zone, id_local_to_utc, 1, &tm);
-    if (utc == Qundef) return 0;
+    if (UNDEF_P(utc)) return 0;
 
     s = extract_time(utc);
     zone_set_offset(zone, tobj, t, s);
@@ -2314,7 +2314,7 @@ zone_localtime(VALUE zone, VALUE time)
     tm = tm_from_time(rb_cTimeTM, time);
 
     local = rb_check_funcall(zone, id_utc_to_local, 1, &tm);
-    if (local == Qundef) return 0;
+    if (UNDEF_P(local)) return 0;
 
     s = extract_vtm(local, &tobj->vtm, subsecx);
     tobj->tm_got = 1;
@@ -2616,7 +2616,7 @@ time_timespec(VALUE num, int interval)
     else {
         i = INT2FIX(1);
         ary = rb_check_funcall(num, id_divmod, 1, &i);
-        if (ary != Qundef && !NIL_P(ary = rb_check_array_type(ary))) {
+        if (!UNDEF_P(ary) && !NIL_P(ary = rb_check_array_type(ary))) {
             i = rb_ary_entry(ary, 0);
             f = rb_ary_entry(ary, 1);
             t.tv_sec = NUM2TIMET(i);
@@ -5481,12 +5481,12 @@ rb_time_zone_abbreviation(VALUE zone, VALUE time)
 
     tm = tm_from_time(rb_cTimeTM, time);
     abbr = rb_check_funcall(zone, rb_intern("abbr"), 1, &tm);
-    if (abbr != Qundef) {
+    if (!UNDEF_P(abbr)) {
         goto found;
     }
 #ifdef SUPPORT_TZINFO_ZONE_ABBREVIATION
     abbr = rb_check_funcall(zone, rb_intern("period_for_utc"), 1, &tm);
-    if (abbr != Qundef) {
+    if (!UNDEF_P(abbr)) {
         abbr = rb_funcallv(abbr, rb_intern("abbreviation"), 0, 0);
         goto found;
     }
@@ -5494,7 +5494,7 @@ rb_time_zone_abbreviation(VALUE zone, VALUE time)
     strftime_args[0] = rb_fstring_lit("%Z");
     strftime_args[1] = tm;
     abbr = rb_check_funcall(zone, rb_intern("strftime"), 2, strftime_args);
-    if (abbr != Qundef) {
+    if (!UNDEF_P(abbr)) {
         goto found;
     }
     abbr = rb_check_funcall_default(zone, idName, 0, 0, Qnil);
diff --git a/timev.rb b/timev.rb
index a2a8bb3cb1577d..6bfb4e5e1b7729 100644
--- a/timev.rb
+++ b/timev.rb
@@ -330,12 +330,17 @@ def self.at(time, subsec = false, unit = :microsecond, in: nil)
   #     Time.new(2000, 1, 1, 0, 0)  # => 2000-01-01 00:00:00 -0600
   #     Time.new(2000, 1, 1, 0, 59) # => 2000-01-01 00:59:00 -0600
   #
-  # - +sec+: Second in range (0..59), or 60 if +usec+ is zero:
+  # - +sec+: Second in range (0...61):
   #
   #     Time.new(2000, 1, 1, 0, 0, 0)  # => 2000-01-01 00:00:00 -0600
   #     Time.new(2000, 1, 1, 0, 0, 59) # => 2000-01-01 00:00:59 -0600
   #     Time.new(2000, 1, 1, 0, 0, 60) # => 2000-01-01 00:01:00 -0600
   #
+  #   +sec+ may be Float or Rational.
+  #
+  #     Time.new(2000, 1, 1, 0, 0, 59.5)  # => 2000-12-31 23:59:59.5 +0900
+  #     Time.new(2000, 1, 1, 0, 0, 59.7r) # => 2000-12-31 23:59:59.7 +0900
+  #
   # These values may be:
   #
   # - Integers, as above.
diff --git a/tool/generic_erb.rb b/tool/generic_erb.rb
index 47bffd830c81dd..6607d5c256e458 100644
--- a/tool/generic_erb.rb
+++ b/tool/generic_erb.rb
@@ -23,6 +23,9 @@
 output = out.path
 vpath = out.vpath
 
+# A hack to prevent "unused variable" warnings
+output, vpath = output, vpath
+
 result = templates.map do |template|
   if ERB.instance_method(:initialize).parameters.assoc(:key) # Ruby 2.6+
     erb = ERB.new(File.read(template), trim_mode: '%-')
diff --git a/tool/mjit/.gitignore b/tool/mjit/.gitignore
deleted file mode 100644
index 66f8ed35a47c74..00000000000000
--- a/tool/mjit/.gitignore
+++ /dev/null
@@ -1 +0,0 @@
-/Gemfile.lock
diff --git a/tool/mjit/Gemfile b/tool/mjit/Gemfile
deleted file mode 100644
index d7f2838765cd5b..00000000000000
--- a/tool/mjit/Gemfile
+++ /dev/null
@@ -1,3 +0,0 @@
-source 'https://rubygems.org'
-
-gem 'ffi-clang', git: 'https://github.com/ioquatix/ffi-clang', ref: 'c08ca683c4f4cf73f4dc38539c3180288b360ea1'
diff --git a/tool/mjit/bindgen.rb b/tool/mjit/bindgen.rb
index 5ffe7166bcd685..c1003fd723e4b4 100755
--- a/tool/mjit/bindgen.rb
+++ b/tool/mjit/bindgen.rb
@@ -1,8 +1,18 @@
 #!/usr/bin/env ruby
 # frozen_string_literal: true
 
-ENV['BUNDLE_GEMFILE'] ||= File.expand_path('./Gemfile', __dir__)
-require 'bundler/setup'
+ENV['GEM_HOME'] = File.expand_path('./.bundle', __dir__)
+require 'rubygems/source'
+require 'bundler/inline'
+gemfile do
+  source 'https://rubygems.org'
+  gem 'ffi-clang', '0.7.0', require: false
+end
+
+# Help ffi-clang find libclang
+# Hint: apt install libclang1
+ENV['LIBCLANG'] ||= Dir.glob("/usr/lib/llvm-*/lib/libclang.so.1").grep_v(/-cpp/).sort.last
+require 'ffi/clang'
 
 require 'etc'
 require 'fiddle/import'
@@ -12,11 +22,6 @@
   abort "Usage: #{$0} BUILD_DIR"
 end
 
-# Help ffi-clang find libclang
-# Hint: apt install libclang1
-ENV['LIBCLANG'] ||= Dir.glob("/lib/#{RUBY_PLATFORM}-gnu/libclang-*.so*").grep_v(/-cpp/).sort.last
-require 'ffi/clang'
-
 class Node < Struct.new(
   :kind,
   :spelling,
@@ -224,7 +229,7 @@ def generate_node(node, sizeof_type: nil)
 
         case child
         # BitField is struct-specific. So it must be handled here.
-        in Node[kind: :field_decl, spelling:, bitwidth:, children: [_grandchild]] if bitwidth > 0
+        in Node[kind: :field_decl, spelling:, bitwidth:, children: [_grandchild, *]] if bitwidth > 0
           buf << field_builder.call(spelling, "CType::BitField.new(#{bitwidth}, #{node.offsetof.fetch(spelling) % 8})")
         # "(unnamed ...)" struct and union are handled here, which are also struct-specific.
         in Node[kind: :field_decl, spelling:, type:, children: [grandchild]] if type.match?(/\((unnamed|anonymous) [^)]+\)\z/)
@@ -341,7 +346,7 @@ def push_target(target)
       VM_METHOD_TYPE_ISEQ
     ],
     UINT: %w[
-      SHAPE_BITS
+      SHAPE_ID_NUM_BITS
       SHAPE_CAPACITY_CHANGE
       SHAPE_FLAG_SHIFT
       SHAPE_FROZEN
diff --git a/tool/test-bundled-gems.rb b/tool/test-bundled-gems.rb
index 12358b69cc43ea..67de52c36c113c 100644
--- a/tool/test-bundled-gems.rb
+++ b/tool/test-bundled-gems.rb
@@ -35,11 +35,6 @@
     test_command << " stdlib_test validate"
     first_timeout *= 3
 
-  when "minitest"
-    # Tentatively exclude some tests that conflict with error_highlight
-    # https://github.com/seattlerb/minitest/pull/880
-    test_command << " 'TESTOPTS=-e /test_stub_value_block_args_5__break_if_not_passed|test_no_method_error_on_unexpected_methods/'"
-
   when "debug"
     # Since debug gem requires debug.so in child processes without
     # acitvating the gem, we preset necessary paths in RUBYLIB
diff --git a/tool/update-deps b/tool/update-deps
index ba94840f658117..f142b30be82bde 100755
--- a/tool/update-deps
+++ b/tool/update-deps
@@ -88,7 +88,6 @@ result.each {|k,v|
 # They can be referenced as $(top_srcdir)/filename.
 # % ruby -e 'def g(d) Dir.chdir(d) { Dir["**/*.{c,h,inc,dmyh}"] } end; puts((g("repo_source_dir_after_build") - g("repo_source_dir_original")).sort)'
 FILES_IN_SOURCE_DIRECTORY = %w[
-  revision.h
 ]
 
 # Files built in the build directory (except extconf.h).
@@ -129,6 +128,7 @@ FILES_NEED_VPATH = %w[
   parse.c
   parse.h
   probes.dmyh
+  revision.h
   vm.inc
   vmtc.inc
 
@@ -340,7 +340,7 @@ def read_single_cc_deps(path_i, cwd)
     next if /\A\# \d+ "(.*)"/ !~ line
     dep = $1
     next if %r{\A<.*>\z} =~ dep # omit <command-line>, etc.
-    next if /\.erb\z/ =~ dep
+    next if /\.e?rb\z/ =~ dep
     compiler_wd ||= dep
     files[dep] = true
   }
diff --git a/transcode.c b/transcode.c
index e315a8f1ab06b2..f1d871e292e794 100644
--- a/transcode.c
+++ b/transcode.c
@@ -2352,7 +2352,7 @@ transcode_loop(const unsigned char **in_pos, unsigned char **out_pos,
                 ec->last_error.error_bytes_len,
                 rb_enc_find(ec->last_error.source_encoding));
         rep = (*fallback_func)(fallback, rep);
-        if (rep != Qundef && !NIL_P(rep)) {
+        if (!UNDEF_P(rep) && !NIL_P(rep)) {
             StringValue(rep);
             ret = rb_econv_insert_output(ec, (const unsigned char *)RSTRING_PTR(rep),
                     RSTRING_LEN(rep), rb_enc_name(rb_enc_get(rep)));
diff --git a/transient_heap.c b/transient_heap.c
index ddf40d104153fc..9dfd980e64b95b 100644
--- a/transient_heap.c
+++ b/transient_heap.c
@@ -169,7 +169,7 @@ ATTRIBUTE_NO_ADDRESS_SAFETY_ANALYSIS(static void transient_heap_ptr_check(struct
 static void
 transient_heap_ptr_check(struct transient_heap *theap, VALUE obj)
 {
-    if (obj != Qundef) {
+    if (!UNDEF_P(obj)) {
         const void *ptr = transient_heap_ptr(obj, FALSE);
         TH_ASSERT(ptr == NULL || transient_header_managed_ptr_p(theap, ptr));
     }
diff --git a/variable.c b/variable.c
index 93abdac454752d..15e18f21aef084 100644
--- a/variable.c
+++ b/variable.c
@@ -281,7 +281,7 @@ rb_path_to_class(VALUE pathname)
             goto undefined_class;
         }
         c = rb_const_search(c, id, TRUE, FALSE, FALSE);
-        if (c == Qundef) goto undefined_class;
+        if (UNDEF_P(c)) goto undefined_class;
         if (!rb_namespace_p(c)) {
             rb_raise(rb_eTypeError, "%"PRIsVALUE" does not refer to class/module",
                      pathname);
@@ -1108,7 +1108,7 @@ gen_ivtbl_count(const struct gen_ivtbl *ivtbl)
     size_t n = 0;
 
     for (i = 0; i < ivtbl->numiv; i++) {
-        if (ivtbl->ivptr[i] != Qundef) {
+        if (!UNDEF_P(ivtbl->ivptr[i])) {
             n++;
         }
     }
@@ -1598,7 +1598,7 @@ iterate_over_shapes_with_callback(rb_shape_t *shape, rb_ivar_foreach_callback_fu
             break;
         }
         VALUE val = iv_list[shape->next_iv_index - 1];
-        if (val != Qundef) {
+        if (!UNDEF_P(val)) {
             callback(shape->edge_name, val, itr_data->arg);
         }
         return;
@@ -1606,6 +1606,7 @@ iterate_over_shapes_with_callback(rb_shape_t *shape, rb_ivar_foreach_callback_fu
       case SHAPE_CAPACITY_CHANGE:
       case SHAPE_FROZEN:
       case SHAPE_IVAR_UNDEF:
+      case SHAPE_T_OBJECT:
         iterate_over_shapes_with_callback(rb_shape_get_parent(shape), callback, itr_data);
         return;
     }
@@ -1756,7 +1757,7 @@ rb_ivar_count(VALUE obj)
             st_index_t i, count, num = ROBJECT_IV_COUNT(obj);
             const VALUE *const ivptr = ROBJECT_IVPTR(obj);
             for (i = count = 0; i < num; ++i) {
-                if (ivptr[i] != Qundef) {
+                if (!UNDEF_P(ivptr[i])) {
                     count++;
                 }
             }
@@ -1773,7 +1774,7 @@ rb_ivar_count(VALUE obj)
                 st_index_t i, num = rb_shape_get_shape(obj)->next_iv_index;
                 const VALUE *const ivptr = RCLASS_IVPTR(obj);
                 for (i = count = 0; i < num; ++i) {
-                    if (ivptr[i] != Qundef) {
+                    if (!UNDEF_P(ivptr[i])) {
                         count++;
                     }
                 }
@@ -2283,7 +2284,7 @@ autoload_synchronized(VALUE _arguments)
     struct autoload_arguments *arguments = (struct autoload_arguments *)_arguments;
 
     rb_const_entry_t *constant_entry = rb_const_lookup(arguments->module, arguments->name);
-    if (constant_entry && constant_entry->value != Qundef) {
+    if (constant_entry && !UNDEF_P(constant_entry->value)) {
         return Qfalse;
     }
 
@@ -2468,7 +2469,7 @@ autoloading_const_entry(VALUE mod, ID id)
 
     // Check if it's being loaded by the current thread/fiber:
     if (autoload_by_current(ele)) {
-        if (ac->value != Qundef) {
+        if (!UNDEF_P(ac->value)) {
             return ac;
         }
     }
@@ -2482,7 +2483,7 @@ autoload_defined_p(VALUE mod, ID id)
     rb_const_entry_t *ce = rb_const_lookup(mod, id);
 
     // If there is no constant or the constant is not undefined (special marker for autoloading):
-    if (!ce || ce->value != Qundef) {
+    if (!ce || !UNDEF_P(ce->value)) {
         // We are not autoloading:
         return 0;
     }
@@ -2578,7 +2579,7 @@ autoload_apply_constants(VALUE _arguments)
 
     // Iterate over all constants and assign them:
     ccan_list_for_each_safe(&arguments->autoload_data->constants, autoload_const, next, cnode) {
-        if (autoload_const->value != Qundef) {
+        if (!UNDEF_P(autoload_const->value)) {
             autoload_const_set(autoload_const);
         }
     }
@@ -2617,7 +2618,7 @@ autoload_try_load(VALUE _arguments)
     // After we loaded the feature, if the constant is not defined, we remove it completely:
     rb_const_entry_t *ce = rb_const_lookup(arguments->module, arguments->name);
 
-    if (!ce || ce->value == Qundef) {
+    if (!ce || UNDEF_P(ce->value)) {
         result = Qfalse;
 
         rb_const_remove(arguments->module, arguments->name);
@@ -2652,7 +2653,7 @@ rb_autoload_load(VALUE module, ID name)
     rb_const_entry_t *ce = rb_const_lookup(module, name);
 
     // We bail out as early as possible without any synchronisation:
-    if (!ce || ce->value != Qundef) {
+    if (!ce || !UNDEF_P(ce->value)) {
         return Qfalse;
     }
 
@@ -2725,7 +2726,7 @@ static VALUE
 rb_const_get_0(VALUE klass, ID id, int exclude, int recurse, int visibility)
 {
     VALUE c = rb_const_search(klass, id, exclude, recurse, visibility);
-    if (c != Qundef) {
+    if (!UNDEF_P(c)) {
         if (UNLIKELY(!rb_ractor_main_p())) {
             if (!rb_ractor_shareable_p(c)) {
                 rb_raise(rb_eRactorIsolationError, "can not access non-shareable objects in constant %"PRIsVALUE"::%s by non-main Ractor.", rb_class_path(klass), rb_id2name(id));
@@ -2769,7 +2770,7 @@ rb_const_search_from(VALUE klass, ID id, int exclude, int recurse, int visibilit
             }
             rb_const_warn_if_deprecated(ce, tmp, id);
             value = ce->value;
-            if (value == Qundef) {
+            if (UNDEF_P(value)) {
                 struct autoload_const *ac;
                 if (am == tmp) break;
                 am = tmp;
@@ -2798,7 +2799,7 @@ rb_const_search(VALUE klass, ID id, int exclude, int recurse, int visibility)
 
     if (klass == rb_cObject) exclude = FALSE;
     value = rb_const_search_from(klass, id, exclude, recurse, visibility);
-    if (value != Qundef) return value;
+    if (!UNDEF_P(value)) return value;
     if (exclude) return value;
     if (BUILTIN_TYPE(klass) != T_MODULE) return value;
     /* search global const too, if klass is a module */
@@ -2935,7 +2936,7 @@ rb_const_remove(VALUE mod, ID id)
 
     val = ce->value;
 
-    if (val == Qundef) {
+    if (UNDEF_P(val)) {
         autoload_delete(mod, id);
         val = Qnil;
     }
@@ -3092,7 +3093,7 @@ rb_const_defined_0(VALUE klass, ID id, int exclude, int recurse, int visibility)
             if (visibility && RB_CONST_PRIVATE_P(ce)) {
                 return (int)Qfalse;
             }
-            if (ce->value == Qundef && !check_autoload_required(tmp, id, 0) &&
+            if (UNDEF_P(ce->value) && !check_autoload_required(tmp, id, 0) &&
                 !rb_autoloading_value(tmp, id, NULL, NULL))
                 return (int)Qfalse;
 
@@ -3298,7 +3299,7 @@ const_tbl_update(struct autoload_const *ac, int autoload_force)
 
     if (rb_id_table_lookup(tbl, id, &value)) {
         ce = (rb_const_entry_t *)value;
-        if (ce->value == Qundef) {
+        if (UNDEF_P(ce->value)) {
             RUBY_ASSERT_CRITICAL_SECTION_ENTER();
             VALUE file = ac->file;
             int line = ac->line;
@@ -3398,7 +3399,7 @@ set_const_visibility(VALUE mod, int argc, const VALUE *argv,
         if ((ce = rb_const_lookup(mod, id))) {
             ce->flag &= ~mask;
             ce->flag |= flag;
-            if (ce->value == Qundef) {
+            if (UNDEF_P(ce->value)) {
                 struct autoload_data *ele;
 
                 ele = autoload_data_for_named_constant(mod, id, &ac);
@@ -3508,7 +3509,7 @@ cvar_lookup_at(VALUE klass, ID id, st_data_t *v)
     }
 
     VALUE n = rb_ivar_lookup(klass, id, Qundef);
-    if (n == Qundef) return 0;
+    if (UNDEF_P(n)) return 0;
 
     if (v) *v = n;
     return 1;
@@ -3838,7 +3839,7 @@ rb_mod_remove_cvar(VALUE mod, VALUE name)
     }
     rb_check_frozen(mod);
     val = rb_ivar_delete(mod, id, Qundef);
-    if (val != Qundef) {
+    if (!UNDEF_P(val)) {
         return (VALUE)val;
     }
     if (rb_cvar_defined(mod, id)) {
diff --git a/vm.c b/vm.c
index eff8a527a96468..d60db5d358c9ef 100644
--- a/vm.c
+++ b/vm.c
@@ -172,7 +172,7 @@ vm_ep_in_heap_p_(const rb_execution_context_t *ec, const VALUE *ep)
     if (VM_EP_IN_HEAP_P(ec, ep)) {
         VALUE envval = ep[VM_ENV_DATA_INDEX_ENV]; /* VM_ENV_ENVVAL(ep); */
 
-        if (envval != Qundef) {
+        if (!UNDEF_P(envval)) {
             const rb_env_t *env = (const rb_env_t *)envval;
 
             VM_ASSERT(vm_assert_env(envval));
@@ -391,7 +391,7 @@ mjit_check_iseq(rb_execution_context_t *ec, const rb_iseq_t *iseq, struct rb_ise
     ASSUME(func_i <= LAST_JIT_ISEQ_FUNC);
     switch ((enum rb_mjit_iseq_func)func_i) {
       case NOT_ADDED_JIT_ISEQ_FUNC:
-        if (body->total_calls == mjit_opts.min_calls) {
+        if (body->total_calls == mjit_opts.call_threshold) {
             rb_mjit_add_iseq_to_process(iseq);
             if (UNLIKELY(mjit_opts.wait && (uintptr_t)body->jit_func > LAST_JIT_ISEQ_FUNC)) {
                 return body->jit_func(ec, ec->cfp);
@@ -1838,7 +1838,7 @@ rb_vm_make_jump_tag_but_local_jump(int state, VALUE val)
       default:
         return Qnil;
     }
-    if (val == Qundef) {
+    if (UNDEF_P(val)) {
         val = GET_EC()->tag->retval;
     }
     return make_localjump_error(mesg, val, state);
@@ -2278,7 +2278,7 @@ vm_exec_enter_vm_loop(rb_execution_context_t *ec, struct rb_vm_exec_context *ctx
 
     ctx->result = ec->errinfo;
     rb_ec_raised_reset(ec, RAISED_STACKOVERFLOW | RAISED_NOMEMORY);
-    while ((ctx->result = vm_exec_handle_exception(ec, ctx->state, ctx->result, &ctx->initial)) == Qundef) {
+    while (UNDEF_P(ctx->result = vm_exec_handle_exception(ec, ctx->state, ctx->result, &ctx->initial))) {
         /* caught a jump, exec the handler */
         ctx->result = vm_exec_core(ec, ctx->initial);
     vm_loop_start:
@@ -2295,7 +2295,7 @@ vm_exec_bottom_main(void *context)
     struct rb_vm_exec_context *ctx = (struct rb_vm_exec_context *)context;
 
     ctx->state = TAG_NONE;
-    if (!ctx->jit_enable_p || (ctx->result = jit_exec(ctx->ec)) == Qundef) {
+    if (!ctx->jit_enable_p || UNDEF_P(ctx->result = jit_exec(ctx->ec))) {
         ctx->result = vm_exec_core(ctx->ec, ctx->initial);
     }
     vm_exec_enter_vm_loop(ctx->ec, ctx, ctx->tag, true);
@@ -2347,7 +2347,7 @@ vm_exec(rb_execution_context_t *ec, bool jit_enable_p)
 
     _tag.retval = Qnil;
     if ((state = EC_EXEC_TAG()) == TAG_NONE) {
-        if (!jit_enable_p || (result = jit_exec(ec)) == Qundef) {
+        if (!jit_enable_p || UNDEF_P(result = jit_exec(ec))) {
             result = vm_exec_core(ec, initial);
         }
         goto vm_loop_start; /* fallback to the VM */
@@ -2355,7 +2355,7 @@ vm_exec(rb_execution_context_t *ec, bool jit_enable_p)
     else {
         result = ec->errinfo;
         rb_ec_raised_reset(ec, RAISED_STACKOVERFLOW | RAISED_NOMEMORY);
-        while ((result = vm_exec_handle_exception(ec, state, result, &initial)) == Qundef) {
+        while (UNDEF_P(result = vm_exec_handle_exception(ec, state, result, &initial))) {
             /* caught a jump, exec the handler */
             result = vm_exec_core(ec, initial);
           vm_loop_start:
diff --git a/vm_args.c b/vm_args.c
index 35adfd94b183ec..0197109b032b67 100644
--- a/vm_args.c
+++ b/vm_args.c
@@ -283,7 +283,7 @@ make_unknown_kw_hash(const VALUE *passed_keywords, int passed_keyword_len, const
     VALUE obj = rb_ary_hidden_new(1);
 
     for (i=0; i<passed_keyword_len; i++) {
-        if (kw_argv[i] != Qundef) {
+        if (!UNDEF_P(kw_argv[i])) {
             rb_ary_push(obj, passed_keywords[i]);
         }
     }
@@ -297,7 +297,7 @@ make_rest_kw_hash(const VALUE *passed_keywords, int passed_keyword_len, const VA
     VALUE obj = rb_hash_new_with_size(passed_keyword_len);
 
     for (i=0; i<passed_keyword_len; i++) {
-        if (kw_argv[i] != Qundef) {
+        if (!UNDEF_P(kw_argv[i])) {
             rb_hash_aset(obj, passed_keywords[i], kw_argv[i]);
         }
     }
@@ -355,7 +355,7 @@ args_setup_kw_parameters(rb_execution_context_t *const ec, const rb_iseq_t *cons
             found++;
         }
         else {
-            if (default_values[di] == Qundef) {
+            if (UNDEF_P(default_values[di])) {
                 locals[i] = Qnil;
 
                 if (LIKELY(i < KW_SPECIFIED_BITS_MAX)) {
diff --git a/vm_eval.c b/vm_eval.c
index eddc6f80da7cfc..c83a88f9fa9d1d 100644
--- a/vm_eval.c
+++ b/vm_eval.c
@@ -621,7 +621,7 @@ check_funcall_missing(rb_execution_context_t *ec, VALUE klass, VALUE recv, ID mi
                                        ID2SYM(mid), Qtrue);
     if (!RTEST(ret)) return def;
     args.respond = respond > 0;
-    args.respond_to_missing = (ret != Qundef);
+    args.respond_to_missing = !UNDEF_P(ret);
     ret = def;
     cme = callable_method_entry(klass, idMethodMissing, &args.defined_class);
 
@@ -684,7 +684,7 @@ rb_check_funcall_default_kw(VALUE recv, ID mid, int argc, const VALUE *argv, VAL
     if (!check_funcall_callable(ec, me)) {
         VALUE ret = check_funcall_missing(ec, klass, recv, mid, argc, argv,
                                           respond, def, kw_splat);
-        if (ret == Qundef) ret = def;
+        if (UNDEF_P(ret)) ret = def;
         return ret;
     }
     stack_check(ec);
@@ -715,7 +715,7 @@ rb_check_funcall_with_hook_kw(VALUE recv, ID mid, int argc, const VALUE *argv,
     if (!check_funcall_callable(ec, me)) {
         VALUE ret = check_funcall_missing(ec, klass, recv, mid, argc, argv,
                                           respond, Qundef, kw_splat);
-        (*hook)(ret != Qundef, recv, mid, argc, argv, arg);
+        (*hook)(!UNDEF_P(ret), recv, mid, argc, argv, arg);
         return ret;
     }
     stack_check(ec);
@@ -846,7 +846,7 @@ rb_method_call_status(rb_execution_context_t *ec, const rb_callable_method_entry
                 defined_class = RBASIC(defined_class)->klass;
             }
 
-            if (self == Qundef || !rb_obj_is_kind_of(self, defined_class)) {
+            if (UNDEF_P(self) || !rb_obj_is_kind_of(self, defined_class)) {
                 return MISSING_PROTECTED;
             }
         }
@@ -1357,7 +1357,7 @@ rb_yield_1(VALUE val)
 VALUE
 rb_yield(VALUE val)
 {
-    if (val == Qundef) {
+    if (UNDEF_P(val)) {
         return rb_yield_0(0, NULL);
     }
     else {
@@ -1698,7 +1698,7 @@ eval_make_iseq(VALUE src, VALUE fname, int line, const rb_binding_t *bind,
         fname = rb_source_location(&line);
     }
 
-    if (fname != Qundef) {
+    if (!UNDEF_P(fname)) {
         if (!NIL_P(fname)) fname = rb_fstring(fname);
     }
     else {
diff --git a/vm_exec.c b/vm_exec.c
index 0f59d08b963507..36bacfd5e84d8e 100644
--- a/vm_exec.c
+++ b/vm_exec.c
@@ -183,7 +183,7 @@ vm_exec_core(rb_execution_context_t *ec, VALUE initial)
         }
     }
 
-    if ((th = rb_ec_thread_ptr(ec))->retval != Qundef) {
+    if (!UNDEF_P((th = rb_ec_thread_ptr(ec))->retval)) {
         VALUE ret = th->retval;
         th->retval = Qundef;
         return ret;
diff --git a/vm_insnhelper.c b/vm_insnhelper.c
index a39b6f87ccc941..5d7d5ddee8f35e 100644
--- a/vm_insnhelper.c
+++ b/vm_insnhelper.c
@@ -1018,7 +1018,7 @@ vm_get_ev_const(rb_execution_context_t *ec, VALUE orig_klass, ID id, bool allow_
                 if ((ce = rb_const_lookup(klass, id))) {
                     rb_const_warn_if_deprecated(ce, klass, id);
                     val = ce->value;
-                    if (val == Qundef) {
+                    if (UNDEF_P(val)) {
                         if (am == klass) break;
                         am = klass;
                         if (is_defined) return 1;
@@ -1212,7 +1212,7 @@ vm_getivar(VALUE obj, ID id, const rb_iseq_t *iseq, IVC ic, const struct rb_call
         }
 
         val = ivar_list[index];
-        RUBY_ASSERT(val != Qundef);
+        RUBY_ASSERT(!UNDEF_P(val));
     }
     else { // cache miss case
 #if RUBY_DEBUG
@@ -1243,7 +1243,7 @@ vm_getivar(VALUE obj, ID id, const rb_iseq_t *iseq, IVC ic, const struct rb_call
 
             // We fetched the ivar list above
             val = ivar_list[index];
-            RUBY_ASSERT(val != Qundef);
+            RUBY_ASSERT(!UNDEF_P(val));
         }
         else {
             if (is_attr) {
@@ -1258,7 +1258,7 @@ vm_getivar(VALUE obj, ID id, const rb_iseq_t *iseq, IVC ic, const struct rb_call
 
     }
 
-    RUBY_ASSERT(val != Qundef);
+    RUBY_ASSERT(!UNDEF_P(val));
 
     return val;
 
@@ -1517,7 +1517,7 @@ vm_getclassvariable(const rb_iseq_t *iseq, const rb_control_frame_t *reg_cfp, ID
         RB_DEBUG_COUNTER_INC(cvar_read_inline_hit);
 
         VALUE v = rb_ivar_lookup(ic->entry->class_value, id, Qundef);
-        RUBY_ASSERT(v != Qundef);
+        RUBY_ASSERT(!UNDEF_P(v));
 
         return v;
     }
@@ -1573,14 +1573,14 @@ vm_setinstancevariable(const rb_iseq_t *iseq, VALUE obj, ID id, VALUE val, IVC i
     attr_index_t index;
     vm_ic_atomic_shape_and_index(ic, &dest_shape_id, &index);
 
-    if (UNLIKELY(vm_setivar(obj, id, val, dest_shape_id, index) == Qundef)) {
+    if (UNLIKELY(UNDEF_P(vm_setivar(obj, id, val, dest_shape_id, index)))) {
         switch (BUILTIN_TYPE(obj)) {
           case T_OBJECT:
           case T_CLASS:
           case T_MODULE:
             break;
           default:
-            if (vm_setivar_default(obj, id, val, dest_shape_id, index) != Qundef) {
+            if (!UNDEF_P(vm_setivar_default(obj, id, val, dest_shape_id, index))) {
                 return;
             }
         }
@@ -2303,7 +2303,7 @@ opt_equality(const rb_iseq_t *cd_owner, VALUE recv, VALUE obj, CALL_DATA cd)
     VM_ASSERT(cd_owner != NULL);
 
     VALUE val = opt_equality_specialized(recv, obj);
-    if (val != Qundef) return val;
+    if (!UNDEF_P(val)) return val;
 
     if (!vm_method_cfunc_is(cd_owner, cd, recv, rb_obj_equal)) {
         return Qundef;
@@ -2337,7 +2337,7 @@ static VALUE
 opt_equality_by_mid(VALUE recv, VALUE obj, ID mid)
 {
     VALUE val = opt_equality_specialized(recv, obj);
-    if (val != Qundef) {
+    if (!UNDEF_P(val)) {
         return val;
     }
     else {
@@ -3301,7 +3301,7 @@ vm_call_attrset_direct(rb_execution_context_t *ec, rb_control_frame_t *cfp, cons
     ID id = vm_cc_cme(cc)->def->body.attr.id;
     rb_check_frozen_internal(obj);
     VALUE res = vm_setivar(obj, id, val, dest_shape_id, index);
-    if (res == Qundef) {
+    if (UNDEF_P(res)) {
         switch (BUILTIN_TYPE(obj)) {
           case T_OBJECT:
           case T_CLASS:
@@ -3310,7 +3310,7 @@ vm_call_attrset_direct(rb_execution_context_t *ec, rb_control_frame_t *cfp, cons
           default:
             {
                 res = vm_setivar_default(obj, id, val, dest_shape_id, index);
-                if (res != Qundef) {
+                if (!UNDEF_P(res)) {
                     return res;
                 }
             }
@@ -4526,7 +4526,7 @@ check_respond_to_missing(VALUE obj, VALUE v)
 
     args[0] = obj; args[1] = Qfalse;
     r = rb_check_funcall(v, idRespond_to_missing, 2, args);
-    if (r != Qundef && RTEST(r)) {
+    if (!UNDEF_P(r) && RTEST(r)) {
         return true;
     }
     else {
@@ -5076,7 +5076,7 @@ vm_sendish(
     }
 #endif
 
-    if (val != Qundef) {
+    if (!UNDEF_P(val)) {
         return val;             /* CFUNC normal return */
     }
     else {
@@ -5094,7 +5094,7 @@ vm_sendish(
         VM_ENV_FLAGS_SET(GET_EP(), VM_FRAME_FLAG_FINISH);
         return vm_exec(ec, true);
     }
-    else if ((val = jit_exec(ec)) == Qundef) {
+    else if (UNDEF_P(val = jit_exec(ec))) {
         VM_ENV_FLAGS_SET(GET_EP(), VM_FRAME_FLAG_FINISH);
         return vm_exec(ec, false);
     }
@@ -5550,7 +5550,7 @@ vm_opt_neq(const rb_iseq_t *iseq, CALL_DATA cd, CALL_DATA cd_eq, VALUE recv, VAL
     if (vm_method_cfunc_is(iseq, cd, recv, rb_obj_not_equal)) {
         VALUE val = opt_equality(iseq, recv, obj, cd_eq);
 
-        if (val != Qundef) {
+        if (!UNDEF_P(val)) {
             return RBOOL(!RTEST(val));
         }
     }
diff --git a/vm_method.c b/vm_method.c
index 08e91ea0392f91..f1c50b9300ebc7 100644
--- a/vm_method.c
+++ b/vm_method.c
@@ -187,6 +187,7 @@ clear_method_cache_by_id_in_class(VALUE klass, ID mid)
         // invalidate CCs
         if (cc_tbl && rb_id_table_lookup(cc_tbl, mid, &ccs_data)) {
             struct rb_class_cc_entries *ccs = (struct rb_class_cc_entries *)ccs_data;
+            rb_yjit_cme_invalidate((rb_callable_method_entry_t *)ccs->cme);
             if (NIL_P(ccs->cme->owner)) invalidate_negative_cache(mid);
             rb_vm_ccs_free(ccs);
             rb_id_table_delete(cc_tbl, mid);
@@ -196,6 +197,10 @@ clear_method_cache_by_id_in_class(VALUE klass, ID mid)
         // remove from callable_m_tbl, if exists
         struct rb_id_table *cm_tbl;
         if ((cm_tbl = RCLASS_CALLABLE_M_TBL(klass)) != NULL) {
+            VALUE cme;
+            if (rb_yjit_enabled_p() && rb_id_table_lookup(cm_tbl, mid, &cme)) {
+                rb_yjit_cme_invalidate((rb_callable_method_entry_t *)cme);
+            }
             rb_id_table_delete(cm_tbl, mid);
             RB_DEBUG_COUNTER_INC(cc_invalidate_leaf_callable);
         }
@@ -255,8 +260,6 @@ clear_method_cache_by_id_in_class(VALUE klass, ID mid)
         }
     }
     RB_VM_LOCK_LEAVE();
-
-    rb_yjit_method_lookup_change(klass, mid);
 }
 
 static void
@@ -2735,7 +2738,7 @@ basic_obj_respond_to(rb_execution_context_t *ec, VALUE obj, ID id, int pub)
       case 0:
         ret = basic_obj_respond_to_missing(ec, klass, obj, ID2SYM(id),
                                            RBOOL(!pub));
-        return RTEST(ret) && ret != Qundef;
+        return RTEST(ret) && !UNDEF_P(ret);
       default:
         return TRUE;
     }
@@ -2847,7 +2850,7 @@ obj_respond_to(int argc, VALUE *argv, VALUE obj)
     if (!(id = rb_check_id(&mid))) {
         VALUE ret = basic_obj_respond_to_missing(ec, CLASS_OF(obj), obj,
                                                  rb_to_symbol(mid), priv);
-        if (ret == Qundef) ret = Qfalse;
+        if (UNDEF_P(ret)) ret = Qfalse;
         return ret;
     }
     return  RBOOL(basic_obj_respond_to(ec, obj, id, !RTEST(priv)));
diff --git a/vm_trace.c b/vm_trace.c
index 3e5cb29156c9f0..ea1d47361d624d 100644
--- a/vm_trace.c
+++ b/vm_trace.c
@@ -262,7 +262,7 @@ remove_event_hook(const rb_execution_context_t *ec, const rb_thread_t *filter_th
     while (hook) {
         if (func == 0 || hook->func == func) {
             if (hook->filter.th == filter_th || filter_th == MATCH_ANY_FILTER_TH) {
-                if (data == Qundef || hook->data == data) {
+                if (UNDEF_P(data) || hook->data == data) {
                     hook->hook_flags |= RUBY_EVENT_HOOK_FLAG_DELETED;
                     ret+=1;
                     list->need_clean = true;
@@ -857,7 +857,7 @@ rb_tracearg_event(rb_trace_arg_t *trace_arg)
 static void
 fill_path_and_lineno(rb_trace_arg_t *trace_arg)
 {
-    if (trace_arg->path == Qundef) {
+    if (UNDEF_P(trace_arg->path)) {
         get_path_and_lineno(trace_arg->ec, trace_arg->cfp, trace_arg->event, &trace_arg->path, &trace_arg->lineno);
     }
 }
@@ -986,7 +986,7 @@ rb_tracearg_return_value(rb_trace_arg_t *trace_arg)
     else {
         rb_raise(rb_eRuntimeError, "not supported by this event");
     }
-    if (trace_arg->data == Qundef) {
+    if (UNDEF_P(trace_arg->data)) {
         rb_bug("rb_tracearg_return_value: unreachable");
     }
     return trace_arg->data;
@@ -1001,7 +1001,7 @@ rb_tracearg_raised_exception(rb_trace_arg_t *trace_arg)
     else {
         rb_raise(rb_eRuntimeError, "not supported by this event");
     }
-    if (trace_arg->data == Qundef) {
+    if (UNDEF_P(trace_arg->data)) {
         rb_bug("rb_tracearg_raised_exception: unreachable");
     }
     return trace_arg->data;
@@ -1018,7 +1018,7 @@ rb_tracearg_eval_script(rb_trace_arg_t *trace_arg)
     else {
         rb_raise(rb_eRuntimeError, "not supported by this event");
     }
-    if (data == Qundef) {
+    if (UNDEF_P(data)) {
         rb_bug("rb_tracearg_raised_exception: unreachable");
     }
     if (rb_obj_is_iseq(data)) {
@@ -1042,7 +1042,7 @@ rb_tracearg_instruction_sequence(rb_trace_arg_t *trace_arg)
     else {
         rb_raise(rb_eRuntimeError, "not supported by this event");
     }
-    if (data == Qundef) {
+    if (UNDEF_P(data)) {
         rb_bug("rb_tracearg_raised_exception: unreachable");
     }
 
@@ -1067,7 +1067,7 @@ rb_tracearg_object(rb_trace_arg_t *trace_arg)
     else {
         rb_raise(rb_eRuntimeError, "not supported by this event");
     }
-    if (trace_arg->data == Qundef) {
+    if (UNDEF_P(trace_arg->data)) {
         rb_bug("rb_tracearg_object: unreachable");
     }
     return trace_arg->data;
diff --git a/win32/Makefile.sub b/win32/Makefile.sub
index e84f978bb72e4f..4b8904c5363b65 100644
--- a/win32/Makefile.sub
+++ b/win32/Makefile.sub
@@ -629,6 +629,9 @@ $(CONFIG_H): $(MKFILES) $(srcdir)/win32/Makefile.sub $(win_srcdir)/Makefile.sub
 #define HAVE_STDDEF_H 1
 #define HAVE_STRING_H 1
 #define HAVE_MEMORY_H 1
+!if $(MSC_VER) >= 1920
+#define HAVE_AFUNIX_H 1
+!endif
 !if $(MSC_VER) >= 1400
 #define HAVE_LONG_LONG 1
 !else
diff --git a/win32/file.c b/win32/file.c
index 243cb1722a0334..e047144d36245e 100644
--- a/win32/file.c
+++ b/win32/file.c
@@ -591,50 +591,6 @@ rb_file_expand_path_internal(VALUE fname, VALUE dname, int abs_mode, int long_na
     return result;
 }
 
-VALUE
-rb_readlink(VALUE path, rb_encoding *resultenc)
-{
-    DWORD len;
-    VALUE wtmp = 0, wpathbuf, str;
-    rb_w32_reparse_buffer_t rbuf, *rp = &rbuf;
-    WCHAR *wpath, *wbuf;
-    rb_encoding *enc;
-    UINT cp, path_cp;
-    int e;
-
-    FilePathValue(path);
-    enc = rb_enc_get(path);
-    cp = path_cp = code_page(enc);
-    if (cp == INVALID_CODE_PAGE) {
-        path = fix_string_encoding(path, enc);
-        cp = CP_UTF8;
-    }
-    len = MultiByteToWideChar(cp, 0, RSTRING_PTR(path), RSTRING_LEN(path), NULL, 0);
-    wpath = ALLOCV_N(WCHAR, wpathbuf, len+1);
-    MultiByteToWideChar(cp, 0, RSTRING_PTR(path), RSTRING_LEN(path), wpath, len);
-    wpath[len] = L'\0';
-    e = rb_w32_read_reparse_point(wpath, rp, sizeof(rbuf), &wbuf, &len);
-    if (e == ERROR_MORE_DATA) {
-        size_t size = rb_w32_reparse_buffer_size(len + 1);
-        rp = ALLOCV(wtmp, size);
-        e = rb_w32_read_reparse_point(wpath, rp, size, &wbuf, &len);
-    }
-    ALLOCV_END(wpathbuf);
-    if (e) {
-        ALLOCV_END(wtmp);
-        if (e != -1)
-            rb_syserr_fail_path(rb_w32_map_errno(e), path);
-        else /* not symlink; maybe volume mount point */
-            rb_syserr_fail_path(EINVAL, path);
-    }
-    enc = resultenc;
-    path_cp = code_page(enc);
-    len = lstrlenW(wbuf);
-    str = append_wstr(rb_enc_str_new(0, 0, enc), wbuf, len, path_cp, enc);
-    ALLOCV_END(wtmp);
-    return str;
-}
-
 int
 rb_file_load_ok(const char *path)
 {
diff --git a/win32/file.h b/win32/file.h
index 36ff27c9b1c744..4f1f36a75cd72a 100644
--- a/win32/file.h
+++ b/win32/file.h
@@ -1,10 +1,12 @@
 #ifndef RUBY_WIN32_FILE_H
 #define RUBY_WIN32_FILE_H
 
-#define MAX_REPARSE_PATH_LEN 4092
+#ifndef IO_REPARSE_TAG_AF_UNIX
+# define IO_REPARSE_TAG_AF_UNIX 0x80000023
+#endif
 
 enum {
-    MINIMUM_REPARSE_BUFFER_PATH_LEN = 4
+    MINIMUM_REPARSE_BUFFER_PATH_LEN = 100
 };
 /* License: Ruby's */
 typedef struct {
@@ -18,14 +20,14 @@ typedef struct {
             USHORT PrintNameOffset;
             USHORT PrintNameLength;
             ULONG  Flags;
-            WCHAR  PathBuffer[4];
+            WCHAR  PathBuffer[MINIMUM_REPARSE_BUFFER_PATH_LEN];
         } SymbolicLinkReparseBuffer;
         struct {
             USHORT SubstituteNameOffset;
             USHORT SubstituteNameLength;
             USHORT PrintNameOffset;
             USHORT PrintNameLength;
-            WCHAR  PathBuffer[4];
+            WCHAR  PathBuffer[MINIMUM_REPARSE_BUFFER_PATH_LEN];
         } MountPointReparseBuffer;
     };
 } rb_w32_reparse_buffer_t;
diff --git a/win32/win32.c b/win32/win32.c
index 865edc8aa68f41..fee31677f0b229 100644
--- a/win32/win32.c
+++ b/win32/win32.c
@@ -49,6 +49,9 @@
 #ifdef __MINGW32__
 #include <mswsock.h>
 #endif
+#ifdef HAVE_AFUNIX_H
+# include <afunix.h>
+#endif
 #include "ruby/win32.h"
 #include "ruby/vm.h"
 #include "win32/dir.h"
@@ -4018,15 +4021,93 @@ rb_w32_getservbyport(int port, const char *proto)
     return r;
 }
 
+#ifdef HAVE_AFUNIX_H
+
+/* License: Ruby's */
+static size_t
+socketpair_unix_path(struct sockaddr_un *sock_un)
+{
+    SOCKET listener;
+    WCHAR wpath[sizeof(sock_un->sun_path)/sizeof(*sock_un->sun_path)] = L"";
+
+    /* AF_UNIX/SOCK_STREAM became available in Windows 10
+     * See https://devblogs.microsoft.com/commandline/af_unix-comes-to-windows
+     */
+    listener = socket(AF_UNIX, SOCK_STREAM, 0);
+    if (listener == INVALID_SOCKET)
+        return 0;
+
+    memset(sock_un, 0, sizeof(*sock_un));
+    sock_un->sun_family = AF_UNIX;
+
+    /* Abstract sockets (filesystem-independent) don't work, contrary to
+     * the claims of the aforementioned blog post:
+     * https://github.com/microsoft/WSL/issues/4240#issuecomment-549663217
+     *
+     * So we must use a named path, and that comes with all the attendant
+     * problems of permissions and collisions. Trying various temporary
+     * directories and putting high-res time and PID in the filename.
+     */
+    for (int try = 0; ; try++) {
+        LARGE_INTEGER ticks;
+        size_t path_len = 0;
+        const size_t maxpath = sizeof(sock_un->sun_path)/sizeof(*sock_un->sun_path);
+
+        switch (try) {
+        case 0:
+            /* user temp dir from TMP or TEMP env var, it ends with a backslash */
+            path_len = GetTempPathW(maxpath, wpath);
+            break;
+        case 1:
+            wcsncpy(wpath, L"C:/Temp/", maxpath);
+            path_len = lstrlenW(wpath);
+            break;
+        case 2:
+            /* Current directory */
+            path_len = 0;
+            break;
+        case 3:
+            closesocket(listener);
+            return 0;
+        }
+
+        /* Windows UNIXSocket implementation expects UTF-8 instead of UTF16 */
+        path_len = WideCharToMultiByte(CP_UTF8, 0, wpath, path_len, sock_un->sun_path, maxpath, NULL, NULL);
+        QueryPerformanceCounter(&ticks);
+        path_len += snprintf(sock_un->sun_path + path_len,
+                 maxpath - path_len,
+                 "%lld-%ld.($)",
+                 ticks.QuadPart,
+                 GetCurrentProcessId());
+
+        /* Convert to UTF16 for DeleteFileW */
+        MultiByteToWideChar(CP_UTF8, 0, sock_un->sun_path, -1, wpath, sizeof(wpath)/sizeof(*wpath));
+
+        if (bind(listener, (struct sockaddr *)sock_un, sizeof(*sock_un)) != SOCKET_ERROR)
+            break;
+    }
+    closesocket(listener);
+    DeleteFileW(wpath);
+    return sizeof(*sock_un);
+}
+#endif
+
 /* License: Ruby's */
 static int
 socketpair_internal(int af, int type, int protocol, SOCKET *sv)
 {
     SOCKET svr = INVALID_SOCKET, r = INVALID_SOCKET, w = INVALID_SOCKET;
     struct sockaddr_in sock_in4;
+
 #ifdef INET6
     struct sockaddr_in6 sock_in6;
 #endif
+
+#ifdef HAVE_AFUNIX_H
+    struct sockaddr_un sock_un = {0, {0}};
+    WCHAR wpath[sizeof(sock_un.sun_path)/sizeof(*sock_un.sun_path)] = L"";
+#endif
+
     struct sockaddr *addr;
     int ret = -1;
     int len;
@@ -4050,6 +4131,15 @@ socketpair_internal(int af, int type, int protocol, SOCKET *sv)
         addr = (struct sockaddr *)&sock_in6;
         len = sizeof(sock_in6);
         break;
+#endif
+#ifdef HAVE_AFUNIX_H
+      case AF_UNIX:
+        addr = (struct sockaddr *)&sock_un;
+        len = socketpair_unix_path(&sock_un);
+        MultiByteToWideChar(CP_UTF8, 0, sock_un.sun_path, -1, wpath, sizeof(wpath)/sizeof(*wpath));
+        if (len)
+            break;
+        /* fall through */
 #endif
       default:
         errno = EAFNOSUPPORT;
@@ -4101,6 +4191,10 @@ socketpair_internal(int af, int type, int protocol, SOCKET *sv)
         }
         if (svr != INVALID_SOCKET)
             closesocket(svr);
+#ifdef HAVE_AFUNIX_H
+        if (sock_un.sun_family == AF_UNIX)
+            DeleteFileW(wpath);
+#endif
     }
 
     return ret;
@@ -5144,32 +5238,35 @@ rb_w32_read_reparse_point(const WCHAR *path, rb_w32_reparse_buffer_t *rp,
 static ssize_t
 w32_readlink(UINT cp, const char *path, char *buf, size_t bufsize)
 {
-    VALUE wtmp;
+    VALUE rp_buf, rp_buf_bigger = 0;
     DWORD len = MultiByteToWideChar(cp, 0, path, -1, NULL, 0);
-    size_t size = rb_w32_reparse_buffer_size(len);
-    WCHAR *wname, *wpath = ALLOCV(wtmp, size + sizeof(WCHAR) * len);
+    size_t size = rb_w32_reparse_buffer_size(bufsize);
+    WCHAR *wname;
+    WCHAR *wpath = ALLOCV(rp_buf, sizeof(WCHAR) * len + size);
     rb_w32_reparse_buffer_t *rp = (void *)(wpath + len);
     ssize_t ret;
     int e;
 
     MultiByteToWideChar(cp, 0, path, -1, wpath, len);
     e = rb_w32_read_reparse_point(wpath, rp, size, &wname, &len);
-    if (e && e != ERROR_MORE_DATA) {
-        ALLOCV_END(wtmp);
-        errno = map_errno(e);
+    if (e == ERROR_MORE_DATA) {
+        size = rb_w32_reparse_buffer_size(len + 1);
+        rp = ALLOCV(rp_buf_bigger, size);
+        e = rb_w32_read_reparse_point(wpath, rp, size, &wname, &len);
+    }
+    if (e) {
+        ALLOCV_END(rp_buf);
+        ALLOCV_END(rp_buf_bigger);
+        errno = e == -1 ? EINVAL : map_errno(e);
         return -1;
     }
-    len = lstrlenW(wname) + 1;
+    len = lstrlenW(wname);
     ret = WideCharToMultiByte(cp, 0, wname, len, buf, bufsize, NULL, NULL);
-    ALLOCV_END(wtmp);
-    if (e) {
+    ALLOCV_END(rp_buf);
+    ALLOCV_END(rp_buf_bigger);
+    if (!ret) {
         ret = bufsize;
     }
-    else if (!ret) {
-        e = GetLastError();
-        errno = map_errno(e);
-        ret = -1;
-    }
     return ret;
 }
 
@@ -5629,10 +5726,8 @@ fileattr_to_unixmode(DWORD attr, const WCHAR *path, unsigned mode)
         /* format is already set */
     }
     else if (attr & FILE_ATTRIBUTE_REPARSE_POINT) {
-        if (rb_w32_reparse_symlink_p(path))
-            mode |= S_IFLNK | S_IEXEC;
-        else
-            mode |= S_IFDIR | S_IEXEC;
+        /* Only used by stat_by_find in the case the file can not be opened.
+         * In this case we can't get more details. */
     }
     else if (attr & FILE_ATTRIBUTE_DIRECTORY) {
         mode |= S_IFDIR | S_IEXEC;
@@ -5707,14 +5802,6 @@ stat_by_find(const WCHAR *path, struct stati128 *st)
 {
     HANDLE h;
     WIN32_FIND_DATAW wfd;
-    /* GetFileAttributesEx failed; check why. */
-    int e = GetLastError();
-
-    if ((e == ERROR_FILE_NOT_FOUND) || (e == ERROR_INVALID_NAME)
-        || (e == ERROR_PATH_NOT_FOUND || (e == ERROR_BAD_NETPATH))) {
-        errno = map_errno(e);
-        return -1;
-    }
 
     /* Fall back to FindFirstFile for ERROR_SHARING_VIOLATION */
     h = FindFirstFileW(path, &wfd);
@@ -5750,9 +5837,24 @@ winnt_stat(const WCHAR *path, struct stati128 *st, BOOL lstat)
     DWORD flags = lstat ? FILE_FLAG_OPEN_REPARSE_POINT : 0;
     HANDLE f;
     WCHAR finalname[PATH_MAX];
+    int open_error;
 
     memset(st, 0, sizeof(*st));
     f = open_special(path, 0, flags);
+    open_error = GetLastError();
+    if (f == INVALID_HANDLE_VALUE && !lstat) {
+        /* Support stat (not only lstat) of UNIXSocket */
+        FILE_ATTRIBUTE_TAG_INFO attr_info;
+        DWORD e;
+
+        f = open_special(path, 0, FILE_FLAG_OPEN_REPARSE_POINT);
+        e = GetFileInformationByHandleEx( f, FileAttributeTagInfo,
+                &attr_info, sizeof(attr_info));
+        if (!e || attr_info.ReparseTag != IO_REPARSE_TAG_AF_UNIX) {
+            CloseHandle(f);
+            f = INVALID_HANDLE_VALUE;
+        }
+    }
     if (f != INVALID_HANDLE_VALUE) {
         DWORD attr = stati128_handle(f, st);
         const DWORD len = get_final_path(f, finalname, numberof(finalname), 0);
@@ -5764,15 +5866,26 @@ winnt_stat(const WCHAR *path, struct stati128 *st, BOOL lstat)
           case FILE_TYPE_PIPE:
             mode = S_IFIFO;
             break;
+          default:
+            if (attr & FILE_ATTRIBUTE_REPARSE_POINT) {
+                FILE_ATTRIBUTE_TAG_INFO attr_info;
+                DWORD e;
+
+                e = GetFileInformationByHandleEx( f, FileAttributeTagInfo,
+                        &attr_info, sizeof(attr_info));
+                if (e && attr_info.ReparseTag == IO_REPARSE_TAG_AF_UNIX) {
+                    st->st_size = 0;
+                    mode |= S_IFSOCK;
+                } else if (rb_w32_reparse_symlink_p(path)) {
+                    /* TODO: size in which encoding? */
+                    st->st_size = 0;
+                    mode |= S_IFLNK | S_IEXEC;
+                } else {
+                    mode |= S_IFDIR | S_IEXEC;
+                }
+            }
         }
         CloseHandle(f);
-        if (attr & FILE_ATTRIBUTE_REPARSE_POINT) {
-            /* TODO: size in which encoding? */
-            if (rb_w32_reparse_symlink_p(path))
-                st->st_size = 0;
-            else
-                attr &= ~FILE_ATTRIBUTE_REPARSE_POINT;
-        }
         if (attr & FILE_ATTRIBUTE_DIRECTORY) {
             if (check_valid_dir(path)) return -1;
         }
@@ -5785,6 +5898,12 @@ winnt_stat(const WCHAR *path, struct stati128 *st, BOOL lstat)
         }
     }
     else {
+        if ((open_error == ERROR_FILE_NOT_FOUND) || (open_error == ERROR_INVALID_NAME)
+            || (open_error == ERROR_PATH_NOT_FOUND || (open_error == ERROR_BAD_NETPATH))) {
+            errno = map_errno(open_error);
+            return -1;
+        }
+
         if (stat_by_find(path, st)) return -1;
     }
 
diff --git a/yjit.c b/yjit.c
index aa49b3cfdca4f6..db0a5f5978a265 100644
--- a/yjit.c
+++ b/yjit.c
@@ -1071,6 +1071,14 @@ rb_yjit_invalidate_all_method_lookup_assumptions(void)
     // method caches, so we do nothing here for now.
 }
 
+// Number of object shapes, which might be useful for investigating YJIT exit reasons.
+static VALUE
+object_shape_count(rb_execution_context_t *ec, VALUE self)
+{
+    // next_shape_id starts from 0, so it's the same as the count
+    return ULONG2NUM((unsigned long)GET_VM()->next_shape_id);
+}
+
 // Primitives used by yjit.rb
 VALUE rb_yjit_stats_enabled_p(rb_execution_context_t *ec, VALUE self);
 VALUE rb_yjit_trace_exit_locations_enabled_p(rb_execution_context_t *ec, VALUE self);
diff --git a/yjit.h b/yjit.h
index 5f2722639f3946..707c0f4b9d92eb 100644
--- a/yjit.h
+++ b/yjit.h
@@ -28,7 +28,6 @@
 bool rb_yjit_enabled_p(void);
 unsigned rb_yjit_call_threshold(void);
 void rb_yjit_invalidate_all_method_lookup_assumptions(void);
-void rb_yjit_method_lookup_change(VALUE klass, ID mid);
 void rb_yjit_cme_invalidate(rb_callable_method_entry_t *cme);
 void rb_yjit_collect_vm_usage_insn(int insn);
 void rb_yjit_collect_binding_alloc(void);
@@ -51,7 +50,6 @@ void rb_yjit_tracing_invalidate_all(void);
 static inline bool rb_yjit_enabled_p(void) { return false; }
 static inline unsigned rb_yjit_call_threshold(void) { return UINT_MAX; }
 static inline void rb_yjit_invalidate_all_method_lookup_assumptions(void) {}
-static inline void rb_yjit_method_lookup_change(VALUE klass, ID mid) {}
 static inline void rb_yjit_cme_invalidate(rb_callable_method_entry_t *cme) {}
 static inline void rb_yjit_collect_vm_usage_insn(int insn) {}
 static inline void rb_yjit_collect_binding_alloc(void) {}
diff --git a/yjit.rb b/yjit.rb
index cac2430127881c..8d67069b1365e9 100644
--- a/yjit.rb
+++ b/yjit.rb
@@ -146,7 +146,10 @@ def self.dump_exit_locations(filename)
   # Return nil when option is not passed or unavailable.
   def self.runtime_stats
     stats = Primitive.rb_yjit_get_stats
-    return stats if stats.nil? || !Primitive.rb_yjit_stats_enabled_p
+    return stats if stats.nil?
+
+    stats[:object_shape_count] = Primitive.object_shape_count
+    return stats unless Primitive.rb_yjit_stats_enabled_p
 
     side_exits = total_exit_count(stats)
     total_exits = side_exits + stats[:leave_interp_return]
@@ -163,6 +166,7 @@ def self.runtime_stats
       # Proportion of instructions that retire in YJIT
       total_insns_count = retired_in_yjit + stats[:vm_insns_count]
       yjit_ratio_pct = 100.0 * retired_in_yjit.to_f / total_insns_count
+      stats[:total_insns_count] = total_insns_count
       stats[:ratio_in_yjit] = yjit_ratio_pct
     end
 
@@ -254,22 +258,25 @@ def _print_stats
       $stderr.puts "bindings_allocations:  " + ("%10d" % stats[:binding_allocations])
       $stderr.puts "bindings_set:          " + ("%10d" % stats[:binding_set])
       $stderr.puts "compilation_failure:   " + ("%10d" % compilation_failure) if compilation_failure != 0
-      $stderr.puts "compiled_block_count:  " + ("%10d" % stats[:compiled_block_count])
       $stderr.puts "compiled_iseq_count:   " + ("%10d" % stats[:compiled_iseq_count])
+      $stderr.puts "compiled_block_count:  " + ("%10d" % stats[:compiled_block_count])
+      $stderr.puts "compiled_branch_count: " + ("%10d" % stats[:compiled_branch_count])
       $stderr.puts "freed_iseq_count:      " + ("%10d" % stats[:freed_iseq_count])
       $stderr.puts "invalidation_count:    " + ("%10d" % stats[:invalidation_count])
       $stderr.puts "constant_state_bumps:  " + ("%10d" % stats[:constant_state_bumps])
       $stderr.puts "inline_code_size:      " + ("%10d" % stats[:inline_code_size])
       $stderr.puts "outlined_code_size:    " + ("%10d" % stats[:outlined_code_size])
       $stderr.puts "freed_code_size:       " + ("%10d" % stats[:freed_code_size])
+      $stderr.puts "code_region_size:      " + ("%10d" % stats[:code_region_size])
       $stderr.puts "yjit_alloc_size:       " + ("%10d" % stats[:yjit_alloc_size]) if stats.key?(:yjit_alloc_size)
       $stderr.puts "live_page_count:       " + ("%10d" % stats[:live_page_count])
       $stderr.puts "freed_page_count:      " + ("%10d" % stats[:freed_page_count])
       $stderr.puts "code_gc_count:         " + ("%10d" % stats[:code_gc_count])
       $stderr.puts "num_gc_obj_refs:       " + ("%10d" % stats[:num_gc_obj_refs])
+      $stderr.puts "object_shape_count:    " + ("%10d" % stats[:object_shape_count])
       $stderr.puts "side_exit_count:       " + ("%10d" % stats[:side_exit_count])
-      $stderr.puts "total_exit_count:      " + ("%10d" % stats[:side_exit_count])
-      $stderr.puts "total_insns_count:     " + ("%10d" % stats[:total_exit_count])
+      $stderr.puts "total_exit_count:      " + ("%10d" % stats[:total_exit_count])
+      $stderr.puts "total_insns_count:     " + ("%10d" % stats[:total_insns_count]) if stats.key?(:total_insns_count)
       if stats.key?(:vm_insns_count)
         $stderr.puts "vm_insns_count:        " + ("%10d" % stats[:vm_insns_count])
       end
diff --git a/yjit/bindgen/src/main.rs b/yjit/bindgen/src/main.rs
index 2b94d95608de6c..9afba864d247b0 100644
--- a/yjit/bindgen/src/main.rs
+++ b/yjit/bindgen/src/main.rs
@@ -85,7 +85,7 @@ fn main() {
         // From shape.h
         .allowlist_function("rb_shape_get_shape_id")
         .allowlist_function("rb_shape_get_shape_by_id")
-        .allowlist_function("rb_shape_flags_mask")
+        .allowlist_function("rb_shape_id_num_bits")
         .allowlist_function("rb_shape_get_iv_index")
 
         // From ruby/internal/intern/object.h
diff --git a/yjit/src/asm/arm64/mod.rs b/yjit/src/asm/arm64/mod.rs
index 683711259e89c2..d4636139438f5f 100644
--- a/yjit/src/asm/arm64/mod.rs
+++ b/yjit/src/asm/arm64/mod.rs
@@ -540,8 +540,6 @@ pub fn ldur(cb: &mut CodeBlock, rt: A64Opnd, rn: A64Opnd) {
 pub fn ldurh(cb: &mut CodeBlock, rt: A64Opnd, rn: A64Opnd) {
     let bytes: [u8; 4] = match (rt, rn) {
         (A64Opnd::Reg(rt), A64Opnd::Mem(rn)) => {
-            assert!(rt.num_bits == 32, "Rt should be a 32 bit register");
-            assert!(rn.num_bits == 64, "Rn should be a 64 bit register");
             assert!(mem_disp_fits_bits(rn.disp), "Expected displacement to be 9 bits or less");
 
             LoadStore::ldurh(rt.reg_no, rn.base_reg_no, rn.disp as i16).into()
diff --git a/yjit/src/asm/mod.rs b/yjit/src/asm/mod.rs
index 4f3d20f5e5f772..728444b281e868 100644
--- a/yjit/src/asm/mod.rs
+++ b/yjit/src/asm/mod.rs
@@ -210,12 +210,15 @@ impl CodeBlock {
         self.page_size
     }
 
+    pub fn mapped_region_size(&self) -> usize {
+        self.mem_block.borrow().mapped_region_size()
+    }
+
     /// Return the number of code pages that have been mapped by the VirtualMemory.
     pub fn num_mapped_pages(&self) -> usize {
-        let mapped_region_size = self.mem_block.borrow().mapped_region_size();
         // CodeBlock's page size != VirtualMem's page size on Linux,
         // so mapped_region_size % self.page_size may not be 0
-        ((mapped_region_size - 1) / self.page_size) + 1
+        ((self.mapped_region_size() - 1) / self.page_size) + 1
     }
 
     /// Return the number of code pages that have been reserved by the VirtualMemory.
diff --git a/yjit/src/asm/x86_64/mod.rs b/yjit/src/asm/x86_64/mod.rs
index 616a54ba7bd129..30fe4072b4b7d5 100644
--- a/yjit/src/asm/x86_64/mod.rs
+++ b/yjit/src/asm/x86_64/mod.rs
@@ -1034,6 +1034,20 @@ pub fn mov(cb: &mut CodeBlock, dst: X86Opnd, src: X86Opnd) {
     };
 }
 
+/// A variant of mov used for always writing the value in 64 bits for GC offsets.
+pub fn movabs(cb: &mut CodeBlock, dst: X86Opnd, value: u64) {
+    match dst {
+        X86Opnd::Reg(reg) => {
+            assert_eq!(reg.num_bits, 64);
+            write_rex(cb, true, 0, 0, reg.reg_no);
+
+            write_opcode(cb, 0xb8, reg);
+            cb.write_int(value, 64);
+        },
+        _ => unreachable!()
+    }
+}
+
 /// movsx - Move with sign extension (signed integers)
 pub fn movsx(cb: &mut CodeBlock, dst: X86Opnd, src: X86Opnd) {
     if let X86Opnd::Reg(_dst_reg) = dst {
diff --git a/yjit/src/asm/x86_64/tests.rs b/yjit/src/asm/x86_64/tests.rs
index 57cc0807102e62..c6d49e084d2e47 100644
--- a/yjit/src/asm/x86_64/tests.rs
+++ b/yjit/src/asm/x86_64/tests.rs
@@ -188,6 +188,12 @@ fn test_mov() {
     check_bytes("48c742f8f4ffffff", |cb| mov(cb, mem_opnd(64, RDX, -8), imm_opnd(-12)));
 }
 
+#[test]
+fn test_movabs() {
+    check_bytes("49b83400000000000000", |cb| movabs(cb, R8, 0x34));
+    check_bytes("49b80000008000000000", |cb| movabs(cb, R8, 0x80000000));
+}
+
 #[test]
 fn test_mov_unsigned() {
     // MOV AL, imm8
diff --git a/yjit/src/backend/arm64/mod.rs b/yjit/src/backend/arm64/mod.rs
index c899f6871f9d1e..cbda5eec054ffa 100644
--- a/yjit/src/backend/arm64/mod.rs
+++ b/yjit/src/backend/arm64/mod.rs
@@ -344,7 +344,14 @@ impl Assembler
                 Insn::Cmp { left, right } => {
                     let opnd0 = split_load_operand(asm, left);
                     let opnd0 = split_less_than_32_cmp(asm, opnd0);
-                    let opnd1 = split_shifted_immediate(asm, right);
+                    let split_right = split_shifted_immediate(asm, right);
+                    let opnd1 = match split_right {
+                        Opnd::InsnOut { .. } if opnd0.num_bits() != split_right.num_bits() => {
+                            split_right.with_num_bits(opnd0.num_bits().unwrap()).unwrap()
+                        },
+                        _ => split_right
+                    };
+
                     asm.cmp(opnd0, opnd1);
                 },
                 Insn::CRet(opnd) => {
@@ -828,6 +835,7 @@ impl Assembler
                         Opnd::Mem(_) => {
                             match opnd.rm_num_bits() {
                                 64 | 32 => ldur(cb, out.into(), opnd.into()),
+                                16 => ldurh(cb, out.into(), opnd.into()),
                                 8 => ldurb(cb, out.into(), opnd.into()),
                                 num_bits => panic!("unexpected num_bits: {}", num_bits)
                             };
@@ -1356,6 +1364,15 @@ mod tests {
         assert_eq!(4, cb.get_write_pos());
     }
 
+    #[test]
+    fn test_32_bit_register_with_some_number() {
+        let (mut asm, mut cb) = setup_asm();
+
+        let shape_opnd = Opnd::mem(32, Opnd::Reg(X0_REG), 6);
+        asm.cmp(shape_opnd, Opnd::UImm(4097));
+        asm.compile_with_num_regs(&mut cb, 2);
+    }
+
     #[test]
     fn test_emit_xor() {
         let (mut asm, mut cb) = setup_asm();
diff --git a/yjit/src/backend/ir.rs b/yjit/src/backend/ir.rs
index 0aa087630d5d42..973fe89b6d0c22 100644
--- a/yjit/src/backend/ir.rs
+++ b/yjit/src/backend/ir.rs
@@ -109,8 +109,8 @@ impl Opnd
                 })
             },
 
-            Opnd::InsnOut{idx, num_bits } => {
-                assert!(num_bits == 64);
+            Opnd::InsnOut{idx, num_bits: out_num_bits } => {
+                assert!(num_bits <= out_num_bits);
                 Opnd::Mem(Mem {
                     base: MemBase::InsnOut(idx),
                     disp: disp,
@@ -143,7 +143,7 @@ impl Opnd
     }
 
     /// Get the size in bits for this operand if there is one.
-    fn num_bits(&self) -> Option<u8> {
+    pub fn num_bits(&self) -> Option<u8> {
         match *self {
             Opnd::Reg(Reg { num_bits, .. }) => Some(num_bits),
             Opnd::Mem(Mem { num_bits, .. }) => Some(num_bits),
diff --git a/yjit/src/backend/x86_64/mod.rs b/yjit/src/backend/x86_64/mod.rs
index dc5f21221da048..68cd35574fd1a6 100644
--- a/yjit/src/backend/x86_64/mod.rs
+++ b/yjit/src/backend/x86_64/mod.rs
@@ -465,15 +465,15 @@ impl Assembler
                 // This assumes only load instructions can contain references to GC'd Value operands
                 Insn::Load { opnd, out } |
                 Insn::LoadInto { dest: out, opnd } => {
-                    mov(cb, out.into(), opnd.into());
-
-                    // If the value being loaded is a heap object
-                    if let Opnd::Value(val) = opnd {
-                        if !val.special_const_p() {
+                    match opnd {
+                        Opnd::Value(val) if val.heap_object_p() => {
+                            // Using movabs because mov might write value in 32 bits
+                            movabs(cb, out.into(), val.0 as _);
                             // The pointer immediate is encoded as the last part of the mov written out
                             let ptr_offset: u32 = (cb.get_write_pos() as u32) - (SIZEOF_VALUE as u32);
                             insn_gc_offsets.push(ptr_offset);
                         }
+                        _ => mov(cb, out.into(), opnd.into())
                     }
                 },
 
diff --git a/yjit/src/codegen.rs b/yjit/src/codegen.rs
index ac70cf98bda24b..c66a29332228cd 100644
--- a/yjit/src/codegen.rs
+++ b/yjit/src/codegen.rs
@@ -721,7 +721,8 @@ pub fn gen_single_block(
 
     #[cfg(feature = "disasm")]
     if get_option_ref!(dump_disasm).is_some() {
-        asm.comment(&format!("Block: {} (ISEQ offset: {})", iseq_get_location(blockid.iseq), blockid.idx));
+        let blockid_idx = blockid.idx;
+        asm.comment(&format!("Block: {} (ISEQ offset: {})", iseq_get_location(blockid.iseq), blockid_idx));
     }
 
     // For each instruction to compile
@@ -829,9 +830,7 @@ pub fn gen_single_block(
         let gc_offsets = asm.compile(cb);
 
         // Add the GC offsets to the block
-        for offset in gc_offsets {
-            block.add_gc_obj_offset(offset)
-        }
+        block.add_gc_obj_offsets(gc_offsets);
 
         // Mark the end position of the block
         block.set_end_addr(cb.get_write_ptr());
@@ -2041,16 +2040,14 @@ fn gen_get_ivar(
     // Compile time self is embedded and the ivar index lands within the object
     let embed_test_result = unsafe { FL_TEST_RAW(comptime_receiver, VALUE(ROBJECT_EMBED.as_usize())) != VALUE(0) };
 
-    let flags_mask: usize = unsafe { rb_shape_flags_mask() }.as_usize();
-    let expected_flags_mask: usize = (RUBY_T_MASK as usize) | !flags_mask | (ROBJECT_EMBED as usize);
-    let expected_flags = comptime_receiver.builtin_flags() & expected_flags_mask;
-
-    // Combined guard for all flags: shape, embeddedness, and T_OBJECT
-    let flags_opnd = Opnd::mem(64, recv, RUBY_OFFSET_RBASIC_FLAGS);
+    let expected_shape = unsafe { rb_shape_get_shape_id(comptime_receiver) };
+    let shape_bit_size = unsafe { rb_shape_id_num_bits() }; // either 16 or 32 depending on RUBY_DEBUG
+    let shape_byte_size = shape_bit_size / 8;
+    let shape_opnd = Opnd::mem(shape_bit_size, recv, RUBY_OFFSET_RBASIC_FLAGS + (8 - shape_byte_size as i32));
 
-    asm.comment("guard shape, embedded, and T_OBJECT");
-    let flags_opnd = asm.and(flags_opnd, Opnd::UImm(expected_flags_mask as u64));
-    asm.cmp(flags_opnd, Opnd::UImm(expected_flags as u64));
+    asm.comment("guard shape");
+    asm.cmp(shape_opnd, Opnd::UImm(expected_shape as u64));
+    let megamorphic_side_exit = counted_exit!(ocb, side_exit, getivar_megamorphic).into();
     jit_chain_guard(
         JCC_JNE,
         jit,
@@ -2058,7 +2055,7 @@ fn gen_get_ivar(
         asm,
         ocb,
         max_chain_depth,
-        side_exit,
+        megamorphic_side_exit,
     );
 
     match ivar_index {
@@ -3895,7 +3892,7 @@ fn jit_obj_respond_to(
     // Invalidate this block if method lookup changes for the method being queried. This works
     // both for the case where a method does or does not exist, as for the latter we asked for a
     // "negative CME" earlier.
-    assume_method_lookup_stable(jit, ocb, recv_class, target_cme);
+    assume_method_lookup_stable(jit, ocb, target_cme);
 
     // Generate a side exit
     let side_exit = get_side_exit(jit, ocb, ctx);
@@ -4179,7 +4176,7 @@ fn gen_send_cfunc(
     }
 
     // Delegate to codegen for C methods if we have it.
-    if kw_arg.is_null() {
+    if kw_arg.is_null() && flags & VM_CALL_OPT_SEND == 0 {
         let codegen_p = lookup_cfunc_codegen(unsafe { (*cme).def });
         if let Some(known_cfunc_codegen) = codegen_p {
             if known_cfunc_codegen(jit, ctx, asm, ocb, ci, cme, block, argc, recv_known_klass) {
@@ -5291,7 +5288,7 @@ fn gen_send_general(
 
     // Register block for invalidation
     //assert!(cme->called_id == mid);
-    assume_method_lookup_stable(jit, ocb, comptime_recv_klass, cme);
+    assume_method_lookup_stable(jit, ocb, cme);
 
     // To handle the aliased method case (VM_METHOD_TYPE_ALIAS)
     loop {
@@ -5470,7 +5467,7 @@ fn gen_send_general(
 
                         flags |= VM_CALL_FCALL | VM_CALL_OPT_SEND;
 
-                        assume_method_lookup_stable(jit, ocb, comptime_recv_klass, cme);
+                        assume_method_lookup_stable(jit, ocb, cme);
 
                         let (known_class, type_mismatch_exit) = {
                             if compile_time_name.string_p() {
@@ -5891,8 +5888,8 @@ fn gen_invokesuper(
 
     // We need to assume that both our current method entry and the super
     // method entry we invoke remain stable
-    assume_method_lookup_stable(jit, ocb, current_defined_class, me);
-    assume_method_lookup_stable(jit, ocb, comptime_superclass, cme);
+    assume_method_lookup_stable(jit, ocb, me);
+    assume_method_lookup_stable(jit, ocb, cme);
 
     // Method calls may corrupt types
     ctx.clear_local_types();
diff --git a/yjit/src/core.rs b/yjit/src/core.rs
index 0dcaa73453e539..869c0859b5e869 100644
--- a/yjit/src/core.rs
+++ b/yjit/src/core.rs
@@ -304,6 +304,7 @@ pub struct Context {
 /// Tuple of (iseq, idx) used to identify basic blocks
 /// There are a lot of blockid objects so we try to keep the size small.
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
+#[repr(packed)]
 pub struct BlockId {
     /// Instruction sequence
     pub iseq: IseqPtr,
@@ -369,13 +370,8 @@ impl Branch {
     }
 }
 
-// In case this block is invalidated, these two pieces of info
-// help to remove all pointers to this block in the system.
-#[derive(Debug)]
-pub struct CmeDependency {
-    pub receiver_klass: VALUE,
-    pub callee_cme: *const rb_callable_method_entry_t,
-}
+// In case a block is invalidated, this helps to remove all pointers to the block.
+pub type CmePtr = *const rb_callable_method_entry_t;
 
 /// Basic block version
 /// Represents a portion of an iseq compiled with a given context
@@ -412,7 +408,7 @@ pub struct Block {
 
     // CME dependencies of this block, to help to remove all pointers to this
     // block in the system.
-    cme_dependencies: Vec<CmeDependency>,
+    cme_dependencies: Vec<CmePtr>,
 
     // Code address of an exit for `ctx` and `blockid`.
     // Used for block invalidation.
@@ -635,9 +631,8 @@ pub extern "C" fn rb_yjit_iseq_mark(payload: *mut c_void) {
             unsafe { rb_gc_mark_movable(block.blockid.iseq.into()) };
 
             // Mark method entry dependencies
-            for cme_dep in &block.cme_dependencies {
-                unsafe { rb_gc_mark_movable(cme_dep.receiver_klass) };
-                unsafe { rb_gc_mark_movable(cme_dep.callee_cme.into()) };
+            for &cme_dep in &block.cme_dependencies {
+                unsafe { rb_gc_mark_movable(cme_dep.into()) };
             }
 
             // Mark outgoing branch entries
@@ -692,8 +687,7 @@ pub extern "C" fn rb_yjit_iseq_update_references(payload: *mut c_void) {
 
             // Update method entry dependencies
             for cme_dep in &mut block.cme_dependencies {
-                cme_dep.receiver_klass = unsafe { rb_gc_location(cme_dep.receiver_klass) };
-                cme_dep.callee_cme = unsafe { rb_gc_location(cme_dep.callee_cme.into()) }.as_cme();
+                *cme_dep = unsafe { rb_gc_location((*cme_dep).into()) }.as_cme();
             }
 
             // Update outgoing branch entries
@@ -884,13 +878,13 @@ fn add_block_version(blockref: &BlockRef, cb: &CodeBlock) {
     let version_list = get_or_create_version_list(block.blockid);
 
     version_list.push(blockref.clone());
+    version_list.shrink_to_fit();
 
     // By writing the new block to the iseq, the iseq now
     // contains new references to Ruby objects. Run write barriers.
     let iseq: VALUE = block.blockid.iseq.into();
-    for dep in block.iter_cme_deps() {
-        obj_written!(iseq, dep.receiver_klass);
-        obj_written!(iseq, dep.callee_cme.into());
+    for &dep in block.iter_cme_deps() {
+        obj_written!(iseq, dep.into());
     }
 
     // Run write barriers for all objects in generated code.
@@ -972,7 +966,7 @@ impl Block {
     }
 
     /// Get an immutable iterator over cme dependencies
-    pub fn iter_cme_deps(&self) -> std::slice::Iter<'_, CmeDependency> {
+    pub fn iter_cme_deps(&self) -> std::slice::Iter<'_, CmePtr> {
         self.cme_dependencies.iter()
     }
 
@@ -1000,22 +994,31 @@ impl Block {
         self.end_idx = end_idx;
     }
 
-    pub fn add_gc_obj_offset(self: &mut Block, ptr_offset: u32) {
-        self.gc_obj_offsets.push(ptr_offset);
-        incr_counter!(num_gc_obj_refs);
+    pub fn add_gc_obj_offsets(self: &mut Block, gc_offsets: Vec<u32>) {
+        for offset in gc_offsets {
+            self.gc_obj_offsets.push(offset);
+            incr_counter!(num_gc_obj_refs);
+        }
+        self.gc_obj_offsets.shrink_to_fit();
     }
 
     /// Instantiate a new CmeDependency struct and add it to the list of
     /// dependencies for this block.
-    pub fn add_cme_dependency(
-        &mut self,
-        receiver_klass: VALUE,
-        callee_cme: *const rb_callable_method_entry_t,
-    ) {
-        self.cme_dependencies.push(CmeDependency {
-            receiver_klass,
-            callee_cme,
-        });
+    pub fn add_cme_dependency(&mut self, callee_cme: CmePtr) {
+        self.cme_dependencies.push(callee_cme);
+        self.cme_dependencies.shrink_to_fit();
+    }
+
+    // Push an incoming branch ref and shrink the vector
+    fn push_incoming(&mut self, branch: BranchRef) {
+        self.incoming.push(branch);
+        self.incoming.shrink_to_fit();
+    }
+
+    // Push an outgoing branch ref and shrink the vector
+    fn push_outgoing(&mut self, branch: BranchRef) {
+        self.outgoing.push(branch);
+        self.outgoing.shrink_to_fit();
     }
 
     // Compute the size of the block code
@@ -1508,8 +1511,7 @@ fn gen_block_series_body(
         last_branch.dst_addrs[0] = new_blockref.borrow().start_addr;
         new_blockref
             .borrow_mut()
-            .incoming
-            .push(last_branchref.clone());
+            .push_incoming(last_branchref.clone());
 
         // Track the block
         batch.push(new_blockref.clone());
@@ -1526,7 +1528,8 @@ fn gen_block_series_body(
             let iseq_location = iseq_get_location(blockid.iseq);
             if iseq_location.contains(substr) {
                 let last_block = last_blockref.borrow();
-                println!("Compiling {} block(s) for {}, ISEQ offsets [{}, {})", batch.len(), iseq_location, blockid.idx, last_block.end_idx);
+                let blockid_idx = blockid.idx;
+                println!("Compiling {} block(s) for {}, ISEQ offsets [{}, {})", batch.len(), iseq_location, blockid_idx, last_block.end_idx);
                 print!("{}", disasm_iseq_insn_range(blockid.iseq, blockid.idx, last_block.end_idx));
             }
         }
@@ -1668,7 +1671,8 @@ fn make_branch_entry(block: &BlockRef, gen_fn: BranchGenFn) -> BranchRef {
 
     // Add to the list of outgoing branches for the block
     let branchref = Rc::new(RefCell::new(branch));
-    block.borrow_mut().outgoing.push(branchref.clone());
+    block.borrow_mut().push_outgoing(branchref.clone());
+    incr_counter!(compiled_branch_count);
 
     return branchref;
 }
@@ -1799,7 +1803,7 @@ fn branch_stub_hit_body(branch_ptr: *const c_void, target_idx: u32, ec: EcPtr) -
             assert!(!(branch.shape == target_branch_shape && block.start_addr != branch.end_addr));
 
             // Add this branch to the list of incoming branches for the target
-            block.incoming.push(branch_rc.clone());
+            block.push_incoming(branch_rc.clone());
 
             // Update the branch target address
             let dst_addr = block.start_addr;
@@ -1847,8 +1851,8 @@ fn branch_stub_hit_body(branch_ptr: *const c_void, target_idx: u32, ec: EcPtr) -
     let new_branch_size = branch.code_size();
     assert!(
         new_branch_size <= branch_size_on_entry,
-        "branch stubs should never enlarge branches: (old_size: {}, new_size: {})",
-        branch_size_on_entry, new_branch_size,
+        "branch stubs should never enlarge branches (start_addr: {:?}, old_size: {}, new_size: {})",
+        branch.start_addr.unwrap().raw_ptr(), branch_size_on_entry, new_branch_size,
     );
 
     // Return a pointer to the compiled block version
@@ -1870,7 +1874,7 @@ fn get_branch_target(
         let mut block = blockref.borrow_mut();
 
         // Add an incoming branch into this block
-        block.incoming.push(branchref.clone());
+        block.push_incoming(branchref.clone());
         let mut branch = branchref.borrow_mut();
         branch.blocks[target_idx.as_usize()] = Some(blockref.clone());
 
@@ -2017,7 +2021,7 @@ pub fn gen_direct_jump(jit: &JITState, ctx: &Context, target0: BlockId, asm: &mu
     if let Some(blockref) = maybe_block {
         let mut block = blockref.borrow_mut();
 
-        block.incoming.push(branchref.clone());
+        block.push_incoming(branchref.clone());
 
         branch.dst_addrs[0] = block.start_addr;
         branch.blocks[0] = Some(blockref.clone());
@@ -2147,7 +2151,8 @@ pub fn invalidate_block_version(blockref: &BlockRef) {
         if let Some(substr) = get_option_ref!(dump_iseq_disasm).as_ref() {
             let iseq_location = iseq_get_location(block.blockid.iseq);
             if iseq_location.contains(substr) {
-                println!("Invalidating block from {}, ISEQ offsets [{}, {})", iseq_location, block.blockid.idx, block.end_idx);
+                let blockid_idx = block.blockid.idx;
+                println!("Invalidating block from {}, ISEQ offsets [{}, {})", iseq_location, blockid_idx, block.end_idx);
             }
         }
     }
@@ -2253,14 +2258,17 @@ pub fn invalidate_block_version(blockref: &BlockRef) {
         }
 
         // Rewrite the branch with the new jump target address
-        let branch_end_addr = branch.end_addr;
+        let old_branch_size = branch.code_size();
         regenerate_branch(cb, &mut branch);
 
         if target_next && branch.end_addr > block.end_addr {
             panic!("yjit invalidate rewrote branch past end of invalidated block: {:?} (code_size: {})", branch, block.code_size());
         }
-        if !target_next && branch.end_addr > branch_end_addr {
-            panic!("invalidated branch grew in size: {:?}", branch);
+        if !target_next && branch.code_size() > old_branch_size {
+            panic!(
+                "invalidated branch grew in size (start_addr: {:?}, old_size: {}, new_size: {})",
+                branch.start_addr.unwrap().raw_ptr(), old_branch_size, branch.code_size()
+            );
         }
     }
 
diff --git a/yjit/src/cruby.rs b/yjit/src/cruby.rs
index 168443e6f0a8a6..d37af383207b30 100644
--- a/yjit/src/cruby.rs
+++ b/yjit/src/cruby.rs
@@ -333,6 +333,11 @@ impl VALUE {
         self.immediate_p() || !self.test()
     }
 
+    /// Return true if the value is a heap object
+    pub fn heap_object_p(self) -> bool {
+        !self.special_const_p()
+    }
+
     /// Return true if the value is a Ruby Fixnum (immediate-size integer)
     pub fn fixnum_p(self) -> bool {
         let VALUE(cval) = self;
diff --git a/yjit/src/cruby_bindings.inc.rs b/yjit/src/cruby_bindings.inc.rs
index 17e5a84c3c6c60..78967cd4ced2ab 100644
--- a/yjit/src/cruby_bindings.inc.rs
+++ b/yjit/src/cruby_bindings.inc.rs
@@ -424,6 +424,9 @@ pub struct rb_shape {
     pub parent_id: shape_id_t,
 }
 pub type rb_shape_t = rb_shape;
+extern "C" {
+    pub fn rb_shape_id_num_bits() -> u8;
+}
 extern "C" {
     pub fn rb_shape_get_shape_by_id(shape_id: shape_id_t) -> *mut rb_shape_t;
 }
@@ -433,9 +436,6 @@ extern "C" {
 extern "C" {
     pub fn rb_shape_get_iv_index(shape: *mut rb_shape_t, id: ID, value: *mut attr_index_t) -> bool;
 }
-extern "C" {
-    pub fn rb_shape_flags_mask() -> VALUE;
-}
 pub const idDot2: ruby_method_ids = 128;
 pub const idDot3: ruby_method_ids = 129;
 pub const idUPlus: ruby_method_ids = 132;
diff --git a/yjit/src/disasm.rs b/yjit/src/disasm.rs
index e958f3bfce0d1c..bab0133c4d949c 100644
--- a/yjit/src/disasm.rs
+++ b/yjit/src/disasm.rs
@@ -90,11 +90,12 @@ pub fn disasm_iseq_insn_range(iseq: IseqPtr, start_idx: u32, end_idx: u32) -> St
             let code_size = block.code_size();
 
             // Write some info about the current block
+            let blockid_idx = blockid.idx;
             let block_ident = format!(
                 "BLOCK {}/{}, ISEQ RANGE [{},{}), {} bytes ",
                 block_idx + 1,
                 block_list.len(),
-                blockid.idx,
+                blockid_idx,
                 end_idx,
                 code_size
             );
diff --git a/yjit/src/invariants.rs b/yjit/src/invariants.rs
index cd3214feae546d..b911ff2c921a5f 100644
--- a/yjit/src/invariants.rs
+++ b/yjit/src/invariants.rs
@@ -25,11 +25,6 @@ pub struct Invariants {
     /// Tracks block assumptions about callable method entry validity.
     cme_validity: HashMap<*const rb_callable_method_entry_t, HashSet<BlockRef>>,
 
-    /// Tracks block assumptions about method lookup. Maps a class to a table of
-    /// method ID points to a set of blocks. While a block `b` is in the table,
-    /// b->callee_cme == rb_callable_method_entry(klass, mid).
-    method_lookup: HashMap<VALUE, HashMap<ID, HashSet<BlockRef>>>,
-
     /// A map from a class and its associated basic operator to a set of blocks
     /// that are assuming that that operator is not redefined. This is used for
     /// quick access to all of the blocks that are making this assumption when
@@ -68,7 +63,6 @@ impl Invariants {
         unsafe {
             INVARIANTS = Some(Invariants {
                 cme_validity: HashMap::new(),
-                method_lookup: HashMap::new(),
                 basic_operator_blocks: HashMap::new(),
                 block_basic_operators: HashMap::new(),
                 single_ractor: HashSet::new(),
@@ -124,34 +118,20 @@ pub fn assume_bop_not_redefined(
 pub fn assume_method_lookup_stable(
     jit: &mut JITState,
     ocb: &mut OutlinedCb,
-    receiver_klass: VALUE,
     callee_cme: *const rb_callable_method_entry_t,
 ) {
-    // RUBY_ASSERT(rb_callable_method_entry(receiver_klass, cme->called_id) == cme);
-    // RUBY_ASSERT_ALWAYS(RB_TYPE_P(receiver_klass, T_CLASS) || RB_TYPE_P(receiver_klass, T_ICLASS));
-    // RUBY_ASSERT_ALWAYS(!rb_objspace_garbage_object_p(receiver_klass));
-
     jit_ensure_block_entry_exit(jit, ocb);
 
     let block = jit.get_block();
     block
         .borrow_mut()
-        .add_cme_dependency(receiver_klass, callee_cme);
+        .add_cme_dependency(callee_cme);
 
     Invariants::get_instance()
         .cme_validity
         .entry(callee_cme)
         .or_default()
         .insert(block.clone());
-
-    let mid = unsafe { (*callee_cme).called_id };
-    Invariants::get_instance()
-        .method_lookup
-        .entry(receiver_klass)
-        .or_default()
-        .entry(mid)
-        .or_default()
-        .insert(block);
 }
 
 // Checks rb_method_basic_definition_p and registers the current block for invalidation if method
@@ -166,7 +146,7 @@ pub fn assume_method_basic_definition(
     ) -> bool {
     if unsafe { rb_method_basic_definition_p(klass, mid) } != 0 {
         let cme = unsafe { rb_callable_method_entry(klass, mid) };
-        assume_method_lookup_stable(jit, ocb, klass, cme);
+        assume_method_lookup_stable(jit, ocb, cme);
         true
     } else {
         false
@@ -272,31 +252,6 @@ pub extern "C" fn rb_yjit_cme_invalidate(callee_cme: *const rb_callable_method_e
     });
 }
 
-/// Callback for when rb_callable_method_entry(klass, mid) is going to change.
-/// Invalidate blocks that assume stable method lookup of `mid` in `klass` when this happens.
-/// This needs to be wrapped on the C side with RB_VM_LOCK_ENTER().
-#[no_mangle]
-pub extern "C" fn rb_yjit_method_lookup_change(klass: VALUE, mid: ID) {
-    // If YJIT isn't enabled, do nothing
-    if !yjit_enabled_p() {
-        return;
-    }
-
-    with_vm_lock(src_loc!(), || {
-        Invariants::get_instance()
-            .method_lookup
-            .entry(klass)
-            .and_modify(|deps| {
-                if let Some(deps) = deps.remove(&mid) {
-                    for block in &deps {
-                        invalidate_block_version(block);
-                        incr_counter!(invalidate_method_lookup);
-                    }
-                }
-            });
-    });
-}
-
 /// Callback for then Ruby is about to spawn a ractor. In that case we need to
 /// invalidate every block that is assuming single ractor mode.
 #[no_mangle]
@@ -387,16 +342,6 @@ pub extern "C" fn rb_yjit_root_mark() {
 
         unsafe { rb_gc_mark(cme) };
     }
-
-    // Mark class and iclass objects
-    for klass in invariants.method_lookup.keys() {
-        // TODO: This is a leak. Unused blocks linger in the table forever, preventing the
-        // callee class they speculate on from being collected.
-        // We could do a bespoke weak reference scheme on classes similar to
-        // the interpreter's call cache. See finalizer for T_CLASS and cc_table_free().
-
-        unsafe { rb_gc_mark(*klass) };
-    }
 }
 
 /// Remove all invariant assumptions made by the block by removing the block as
@@ -410,17 +355,9 @@ pub fn block_assumptions_free(blockref: &BlockRef) {
         // For each method lookup dependency
         for dep in block.iter_cme_deps() {
             // Remove tracking for cme validity
-            if let Some(blockset) = invariants.cme_validity.get_mut(&dep.callee_cme) {
+            if let Some(blockset) = invariants.cme_validity.get_mut(dep) {
                 blockset.remove(blockref);
             }
-
-            // Remove tracking for lookup stability
-            if let Some(id_to_block_set) = invariants.method_lookup.get_mut(&dep.receiver_klass) {
-                let mid = unsafe { (*dep.callee_cme).called_id };
-                if let Some(block_set) = id_to_block_set.get_mut(&mid) {
-                    block_set.remove(&blockref);
-                }
-            }
         }
     }
 
diff --git a/yjit/src/stats.rs b/yjit/src/stats.rs
index cfce4c9c33f2b6..03eec21b50bc42 100644
--- a/yjit/src/stats.rs
+++ b/yjit/src/stats.rs
@@ -267,6 +267,7 @@ make_counters! {
     vm_insns_count,
     compiled_iseq_count,
     compiled_block_count,
+    compiled_branch_count,
     compilation_failure,
     freed_iseq_count,
 
@@ -402,6 +403,9 @@ fn rb_yjit_gen_stats_dict() -> VALUE {
         // Code GC count
         hash_aset_usize!(hash, "code_gc_count", CodegenGlobals::get_code_gc_count());
 
+        // Size of memory region allocated for JIT code
+        hash_aset_usize!(hash, "code_region_size", cb.mapped_region_size());
+
         // Rust global allocations in bytes
         #[cfg(feature="stats")]
         hash_aset_usize!(hash, "yjit_alloc_size", global_allocation_size());
diff --git a/yjit/src/virtualmem.rs b/yjit/src/virtualmem.rs
index 1d80983c9e9e44..668e3d6a7b84d5 100644
--- a/yjit/src/virtualmem.rs
+++ b/yjit/src/virtualmem.rs
@@ -59,7 +59,7 @@ pub trait Allocator {
 /// We may later change this to wrap an u32.
 /// Note: there is no NULL constant for CodePtr. You should use Option<CodePtr> instead.
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Debug)]
-#[repr(C)]
+#[repr(C, packed)]
 pub struct CodePtr(*const u8);
 
 /// Errors that can happen when writing to [VirtualMemory]