Add NEWS entries about JIT in Jul ~ Dec

* Instance variables
  * Merge ivar guards on JIT a69dd69 e4f7eee
  * Prefer RB_OBJ_FROZEN_RAW 5611066
  * Skip checking ROBJECT_EMBED 81a8d1c
* Method inlining
  * Mark some Integer methods as inline 0703e01
  * Allow inlining Integer#-@ and #~ dbb4f19
  * Inline builtin struct aref 167d139
  * Make Kernel#then, #yield_self, #frozen? builtin 24fa37d
  * (For future) Rewrite Kernel#tap with Ruby f3a0d7a
* Other optimizations
  * Inline constant references 53babf3
  * Lazily move PC with RUBY_VM_CHECK_INTS 5d74894
  * Cache access to reg_cfp->self on JIT d409837
* JIT compaction
  * Shrink the blocking region for compile_compact_jit_code ed8e552
  * Stop leaving .c files for JIT compaction in /tmp fa1250a
* GC of JIT-ed code
  * Run unload_units in the JIT worker thread 16dab6b
  * Avoid unloading units which have enough total_calls d80226e
  * Throttle unload_units 122cd35
  * Throttle JIT compaction 096f544
* Compilation speed
  * Eliminate IVC sync between JIT and Ruby threads 0960f56
  * Lazily move units from active_units to stale_units 5d8f227

Please see 200c5f4 for other improvements in Jan ~ Jun.

NEWS.md

@@ -630,22 +630,51 @@ Excluding feature bug fixes.
 
 ### JIT
 
-* Native functions shared by multiple methods are deduplicated on JIT compaction.
+* Performance improvements of JIT-ed code
 
-* Decrease code size of hot paths by some optimizations and partitioning cold paths.
+    * Microarchitectural optimizations
 
-* Not only pure Ruby methods but also some C methods skip pushing a method frame.
+        * Native functions shared by multiple methods are deduplicated on JIT compaction.
 
-    * `Kernel#class`, `Integer#zero?`
+        * Decrease code size of hot paths by some optimizations and partitioning cold paths.
 
-* Always generate appropriate code for `==`, `nil?`, and `!` calls depending on
-  a receiver class.
+    * Instance variables
 
-* Optimize instance variable access in some core classes like Hash and their subclasses.
+        * Eliminate some redundant checks.
 
-* Eliminate VM register access on a method return.
+        * Skip checking a class and a object multiple times in a method when possible.
 
-* Optimize C method calls a little.
+        * Optimize accesses in some core classes like Hash and their subclasses.
+
+    * Method inlining support for some C methods
+
+        * `Kernel`: `#class`, `#frozen?`
+
+        * `Integer`: `#-@`, `#~`, `#abs`, `#bit_length`, `#even?`, `#integer?`, `#magnitude`,
+          `#odd?`, `#ord`, `#to_i`, `#to_int`, `#zero?`
+
+        * `Struct`: reader methods for 10th or later members
+
+    * Constant references are inlined.
+
+    * Always generate appropriate code for `==`, `nil?`, and `!` calls depending on
+      a receiver class.
+
+    * Reduce the number of VM register accesses on branches and method returns.
+
+    * Optimize C method calls a little.
+
+* Compilation process improvements
+
+    * It does not keep temporary files in /tmp anymore.
+
+    * Throttle GC and compaction of JIT-ed code.
+
+    * Avoid GC-ing JIT-ed code when not necessary.
+
+    * GC-ing JIT-ed code is executed in a background thread.
+
+    * Reduce the number of locks between Ruby and JIT threads.
 
 ## Static analysis