Add generic ivar reference updating step

Previously, generic ivars worked differently than the other global tables
during compaction. The other global tables had their references updated
through iteration during rb_gc_update_vm_references. Generic ivars updated
the keys when the object moved and updated the values while reference
updating the object. This is inefficient as this required one lookup for
every moved object and one lookup for every object with generic ivars.

Instead, this commit changes it to iterate over the generic ivar table to
update both the keys and values.

gc.c

@@ -3492,6 +3492,7 @@ rb_gc_update_vm_references(void *objspace)
     rb_vm_t *vm = rb_ec_vm_ptr(ec);
 
     rb_vm_update_references(vm);
+    rb_generic_ivar_update_references();
     rb_gc_update_global_tbl();
     global_symbols.ids = gc_location_internal(objspace, global_symbols.ids);
     global_symbols.dsymbol_fstr_hash = gc_location_internal(objspace, global_symbols.dsymbol_fstr_hash);
@@ -3509,10 +3510,6 @@ rb_gc_update_vm_references(void *objspace)
 void
 rb_gc_update_object_references(void *objspace, VALUE obj)
 {
-    if (FL_TEST(obj, FL_EXIVAR)) {
-        rb_ref_update_generic_ivar(obj);
-    }
-
     switch (BUILTIN_TYPE(obj)) {
       case T_CLASS:
         if (FL_TEST(obj, FL_SINGLETON)) {

gc/default/default.c

@@ -6927,15 +6927,6 @@ gc_move(rb_objspace_t *objspace, VALUE src, VALUE dest, size_t src_slot_size, si
     CLEAR_IN_BITMAP(GET_HEAP_UNCOLLECTIBLE_BITS(src), src);
     CLEAR_IN_BITMAP(GET_HEAP_PAGE(src)->remembered_bits, src);
 
-    if (FL_TEST(src, FL_EXIVAR)) {
-        /* Resizing the st table could cause a malloc */
-        DURING_GC_COULD_MALLOC_REGION_START();
-        {
-            rb_mv_generic_ivar(src, dest);
-        }
-        DURING_GC_COULD_MALLOC_REGION_END();
-    }
-
     if (FL_TEST(src, FL_SEEN_OBJ_ID)) {
         /* If the source object's object_id has been seen, we need to update
          * the object to object id mapping. */

internal/variable.h

@@ -50,12 +50,11 @@ int rb_gen_ivtbl_get(VALUE obj, ID id, struct gen_ivtbl **ivtbl);
 void rb_obj_copy_ivs_to_hash_table(VALUE obj, st_table *table);
 void rb_obj_convert_to_too_complex(VALUE obj, st_table *table);
 void rb_evict_ivars_to_hash(VALUE obj);
+void rb_generic_ivar_update_references(void);
 
 RUBY_SYMBOL_EXPORT_BEGIN
 /* variable.c (export) */
 void rb_mark_generic_ivar(VALUE obj);
-void rb_ref_update_generic_ivar(VALUE);
-void rb_mv_generic_ivar(VALUE src, VALUE dst);
 VALUE rb_const_missing(VALUE klass, VALUE name);
 int rb_class_ivar_set(VALUE klass, ID vid, VALUE value);
 void rb_iv_tbl_copy(VALUE dst, VALUE src);

variable.c

@@ -1136,31 +1136,40 @@ rb_mark_generic_ivar(VALUE obj)
     }
 }
 
-void
-rb_ref_update_generic_ivar(VALUE obj)
+static int
+rb_generic_ivar_update_references_i(st_data_t key, st_data_t val, st_data_t _data)
 {
-    struct gen_ivtbl *ivtbl;
+    VALUE orig_obj = (VALUE)key;
+    VALUE obj = rb_gc_location(orig_obj);
+    struct gen_ivtbl *ivtbl = (struct gen_ivtbl *)val;
 
-    if (rb_gen_ivtbl_get(obj, 0, &ivtbl)) {
-        if (rb_shape_obj_too_complex(obj)) {
-            rb_gc_ref_update_table_values_only(ivtbl->as.complex.table);
-        }
-        else {
-            for (uint32_t i = 0; i < ivtbl->as.shape.numiv; i++) {
-                ivtbl->as.shape.ivptr[i] = rb_gc_location(ivtbl->as.shape.ivptr[i]);
-            }
+    if (rb_shape_obj_too_complex(obj)) {
+        rb_gc_ref_update_table_values_only(ivtbl->as.complex.table);
+    }
+    else {
+        for (uint32_t i = 0; i < ivtbl->as.shape.numiv; i++) {
+            ivtbl->as.shape.ivptr[i] = rb_gc_location(ivtbl->as.shape.ivptr[i]);
         }
     }
+
+    if (obj != orig_obj) {
+        st_insert(generic_iv_tbl_, (st_data_t)obj, (st_data_t)ivtbl);
+
+        return ST_DELETE;
+    }
+    else {
+        return ST_CONTINUE;
+    }
 }
 
 void
-rb_mv_generic_ivar(VALUE rsrc, VALUE dst)
+rb_generic_ivar_update_references(void)
 {
-    st_data_t key = (st_data_t)rsrc;
-    st_data_t ivtbl;
-
-    if (st_delete(generic_ivtbl_no_ractor_check(rsrc), &key, &ivtbl))
-        st_insert(generic_ivtbl_no_ractor_check(dst), (st_data_t)dst, ivtbl);
+    DURING_GC_COULD_MALLOC_REGION_START();
+    {
+        st_foreach(generic_iv_tbl_, rb_generic_ivar_update_references_i, (st_data_t)0);
+    }
+    DURING_GC_COULD_MALLOC_REGION_END();
 }
 
 void