Remove the uninitialized instance variable verbose mode warning

This speeds up all instance variable access, even when not in
verbose mode.  Uninitialized instance variable warnings were
rarely helpful, and resulted in slower code if you wanted to
avoid warnings when run in verbose mode.

Implements [Feature #17055]

NEWS.md

@@ -582,6 +582,8 @@ end
   message and backtrace are printed in order from the innermost.
   [[Feature #8661]]
 
+* Accessing an uninitialized instance variable no longer emits a
+  warning in verbose mode. [[Feature #17055]]
 
 [Bug #4352]:      https://bugs.ruby-lang.org/issues/4352
 [Bug #6087]:      https://bugs.ruby-lang.org/issues/6087
@@ -629,6 +631,7 @@ end
 [Feature #16815]: https://bugs.ruby-lang.org/issues/16815
 [Feature #16828]: https://bugs.ruby-lang.org/issues/16828
 [Misc #16961]:    https://bugs.ruby-lang.org/issues/16961
+[Feature #17055]: https://bugs.ruby-lang.org/issues/17055
 [Feature #17104]: https://bugs.ruby-lang.org/issues/17104
 [Feature #17122]: https://bugs.ruby-lang.org/issues/17122
 [Feature #17134]: https://bugs.ruby-lang.org/issues/17134

test/-ext-/symbol/test_inadvertent_creation.rb

@@ -485,10 +485,8 @@ def test_kwarg_symbol_leak_just_rest
 
     def test_iv_get
       obj = Object.new
-      assert_warning(/not initialized/) do
-        assert_no_immortal_symbol_created("rb_iv_get") do |name|
-          Bug::Symbol.iv_get(obj, name)
-        end
+      assert_no_immortal_symbol_created("rb_iv_get") do |name|
+        Bug::Symbol.iv_get(obj, name)
       end
     end
   end

test/ruby/test_exception.rb

@@ -955,8 +955,8 @@ def capture_warning_warn(category: false)
   end
 
   def test_warning_warn
-    warning = capture_warning_warn {@a}
-    assert_match(/instance variable @a not initialized/, warning[0])
+    warning = capture_warning_warn {$asdfasdsda_test_warning_warn}
+    assert_match(/global variable `\$asdfasdsda_test_warning_warn' not initialized/, warning[0])
 
     assert_equal(["a\nz\n"], capture_warning_warn {warn "a\n", "z"})
     assert_equal([],         capture_warning_warn {warn})
@@ -1040,7 +1040,7 @@ def test_warning_warn_circular_require_backtrace
   end
 
   def test_warning_warn_super
-    assert_in_out_err(%[-W0], "#{<<~"{#"}\n#{<<~'};'}", [], /instance variable @a not initialized/)
+    assert_in_out_err(%[-W0], "#{<<~"{#"}\n#{<<~'};'}", [], /global variable `\$asdfiasdofa_test_warning_warn_super' not initialized/)
     {#
       module Warning
         def warn(message)
@@ -1049,7 +1049,7 @@ def warn(message)
       end
 
       $VERBOSE = true
-      @a
+      $asdfiasdofa_test_warning_warn_super
     };
   end
 

test/ruby/test_jit.rb

@@ -829,11 +829,9 @@ def bar
         end
       end
 
-      verbose, $VERBOSE = $VERBOSE, false # suppress "instance variable @b not initialized"
       print(Foo.new.bar)
       print(Foo.new.bar)
       print(Foo.new.bar)
-      $VERBOSE = verbose
     end;
   end
 

test/ruby/test_module.rb

@@ -2401,7 +2401,7 @@ def ivar
 
   def test_uninitialized_instance_variable
     a = AttrTest.new
-    assert_warning(/instance variable @ivar not initialized/) do
+    assert_warning('') do
       assert_nil(a.ivar)
     end
     a.instance_variable_set(:@ivar, 42)
@@ -2410,7 +2410,7 @@ def test_uninitialized_instance_variable
     end
 
     name = "@\u{5909 6570}"
-    assert_warning(/instance variable #{name} not initialized/) do
+    assert_warning('') do
       assert_nil(a.instance_eval(name))
     end
   end

variable.c

@@ -1217,14 +1217,8 @@ rb_ivar_lookup(VALUE obj, ID id, VALUE undef)
 VALUE
 rb_ivar_get(VALUE obj, ID id)
 {
-    VALUE iv = rb_ivar_lookup(obj, id, Qundef);
+    VALUE iv = rb_ivar_lookup(obj, id, Qnil);
     RB_DEBUG_COUNTER_INC(ivar_get_base);
-
-    if (iv == Qundef) {
-	if (RTEST(ruby_verbose))
-	    rb_warning("instance variable %"PRIsVALUE" not initialized", QUOTE_ID(id));
-	iv = Qnil;
-    }
     return iv;
 }
 
@@ -3526,8 +3520,6 @@ rb_iv_get(VALUE obj, const char *name)
     ID id = rb_check_id_cstr(name, strlen(name), rb_usascii_encoding());
 
     if (!id) {
-        if (RTEST(ruby_verbose))
-            rb_warning("instance variable %s not initialized", name);
         return Qnil;
     }
     return rb_ivar_get(obj, id);

vm_insnhelper.c

@@ -1179,9 +1179,6 @@ vm_getivar(VALUE obj, ID id, const rb_iseq_t *iseq, IVC ic, const struct rb_call
             return val;
         }
         else {
-            if (!is_attr && RTEST(ruby_verbose)) {
-                rb_warning("instance variable %"PRIsVALUE" not initialized", QUOTE_ID(id));
-            }
             return Qnil;
         }
     }