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, 16 insertions, 3 deletions

diff --git a/gc.c b/gc.c
index f8810d1af6..ad2406c98b 100644
--- a/gc.c
+++ b/gc.c
@@ -2398,6 +2398,7 @@ rb_imemo_name(enum imemo_type type)
         IMEMO_NAME(parser_strterm);
         IMEMO_NAME(callinfo);
         IMEMO_NAME(callcache);
+        IMEMO_NAME(constcache);
 #undef IMEMO_NAME
     }
     return "unknown";
@@ -3102,9 +3103,9 @@ obj_free(rb_objspace_t *objspace, VALUE obj)
           case imemo_callcache:
             RB_DEBUG_COUNTER_INC(obj_imemo_callcache);
             break;
-	  default:
-            /* unreachable */
-	    break;
+          case imemo_constcache:
+            RB_DEBUG_COUNTER_INC(obj_imemo_constcache);
+            break;
 	}
 	return 0;
 
@@ -6260,6 +6261,12 @@ gc_mark_imemo(rb_objspace_t *objspace, VALUE obj)
             gc_mark(objspace, (VALUE)vm_cc_cme(cc));
         }
         return;
+      case imemo_constcache:
+        {
+            const struct iseq_inline_constant_cache_entry *ice = (struct iseq_inline_constant_cache_entry *)obj;
+            gc_mark(objspace, ice->value);
+        }
+        return;
 #if VM_CHECK_MODE > 0
       default:
 	VM_UNREACHABLE(gc_mark_imemo);
@@ -8985,6 +8992,12 @@ gc_ref_update_imemo(rb_objspace_t *objspace, VALUE obj)
             }
         }
         break;
+      case imemo_constcache:
+        {
+            const struct iseq_inline_constant_cache_entry *ice = (struct iseq_inline_constant_cache_entry *)obj;
+            UPDATE_IF_MOVED(objspace, ice->value);
+        }
+        break;
       case imemo_parser_strterm:
       case imemo_tmpbuf:
       case imemo_callinfo: