enable constant cache on ractors

constant cache `IC` is accessed by non-atomic manner and there are
thread-safety issues, so Ruby 3.0 disables to use const cache on
non-main ractors.

This patch enables it by introducing `imemo_constcache` and allocates
it by every re-fill of const cache like `imemo_callcache`.
[Bug #17510]

Now `IC` only has one entry `IC::entry` and it points to
`iseq_inline_constant_cache_entry`, managed by T_IMEMO object.

`IC` is atomic data structure so `rb_mjit_before_vm_ic_update()` and
`rb_mjit_after_vm_ic_update()` is not needed.

1 files changed, 13 insertions, 9 deletions

diff --git a/test/ruby/test_gc.rb b/test/ruby/test_gc.rb
index 1823538f73..daa8b5c37a 100644
--- a/test/ruby/test_gc.rb
+++ b/test/ruby/test_gc.rb
@@ -92,19 +92,23 @@ class TestGc < Test::Unit::TestCase
     assert_kind_of(Integer, res[:count])
 
     stat, count = {}, {}
-    GC.start
-    GC.stat(stat)
-    ObjectSpace.count_objects(count)
-    # repeat same methods invocation for cache object creation.
-    GC.stat(stat)
-    ObjectSpace.count_objects(count)
+    2.times{ # to ignore const cache imemo creation
+      GC.start
+      GC.stat(stat)
+      ObjectSpace.count_objects(count)
+      # repeat same methods invocation for cache object creation.
+      GC.stat(stat)
+      ObjectSpace.count_objects(count)
+    }
     assert_equal(count[:TOTAL]-count[:FREE], stat[:heap_live_slots])
     assert_equal(count[:FREE], stat[:heap_free_slots])
 
     # measure again without GC.start
-    1000.times{ "a" + "b" }
-    GC.stat(stat)
-    ObjectSpace.count_objects(count)
+    2.times{ # to ignore const cache imemo creation
+      1000.times{ "a" + "b" }
+      GC.stat(stat)
+      ObjectSpace.count_objects(count)
+    }
     assert_equal(count[:FREE], stat[:heap_free_slots])
   end