Remove write barrier exemption for T_ICLASS

Before this commit, iclasses were "shady", or not protected by write
barriers. Because of that, the GC needs to spend more time marking these
objects than otherwise.

Applications that make heavy use of modules should see reduction in GC
time as they have a significant number of live iclasses on the heap.

 - Put logic for iclass method table ownership into a function
 - Remove calls to WB_UNPROTECT and insert write barriers for iclasses

This commit relies on the following invariant: for any non oirigin
iclass `I`, `RCLASS_M_TBL(I) == RCLASS_M_TBL(RBasic(I)->klass)`. This
invariant did not hold prior to 98286e9 for classes and modules that
have prepended modules.

[Feature #16984]

1 files changed, 3 insertions, 6 deletions

diff --git a/class.c b/class.c
index 0d97603821..9876e996c8 100644
--- a/class.c
+++ b/class.c
@@ -911,8 +911,7 @@ rb_include_class_new(VALUE module, VALUE super)
 {
     VALUE klass = class_alloc(T_ICLASS, rb_cClass);
 
-    RCLASS_M_TBL(OBJ_WB_UNPROTECT(klass)) =
-      RCLASS_M_TBL(OBJ_WB_UNPROTECT(module)); /* TODO: unprotected? */
+    RCLASS_M_TBL(klass) = RCLASS_M_TBL(module);
 
     RCLASS_SET_ORIGIN(klass, klass);
     if (BUILTIN_TYPE(module) == T_ICLASS) {
@@ -1098,13 +1097,12 @@ move_refined_method(ID key, VALUE value, void *data)
 	    const rb_method_entry_t *orig_me = me->def->body.refined.orig_me, *new_me;
 	    RB_OBJ_WRITE(me, &me->def->body.refined.orig_me, NULL);
 	    new_me = rb_method_entry_clone(me);
-	    rb_id_table_insert(tbl, key, (VALUE)new_me);
-	    RB_OBJ_WRITTEN(klass, Qundef, new_me);
+            rb_method_table_insert(klass, tbl, key, new_me);
 	    rb_method_entry_copy(me, orig_me);
 	    return ID_TABLE_CONTINUE;
 	}
 	else {
-	    rb_id_table_insert(tbl, key, (VALUE)me);
+            rb_method_table_insert(klass, tbl, key, me);
 	    return ID_TABLE_DELETE;
 	}
     }
@@ -1119,7 +1117,6 @@ ensure_origin(VALUE klass)
     VALUE origin = RCLASS_ORIGIN(klass);
     if (origin == klass) {
 	origin = class_alloc(T_ICLASS, klass);
-	OBJ_WB_UNPROTECT(origin); /* TODO: conservative shading. Need more survey. */
 	RCLASS_SET_SUPER(origin, RCLASS_SUPER(klass));
 	RCLASS_SET_SUPER(klass, origin);
 	RCLASS_SET_ORIGIN(klass, origin);