Stop zeroing memory on allocation / copy

Shapes gives us an almost exact count of instance variables on an
object.  Since we know the number of instance variables that have been
set, we will never access slots that haven't been initialized with an
IV.

gc.c

@@ -2919,40 +2919,28 @@ rb_class_instance_allocate_internal(VALUE klass, VALUE flags, bool wb_protected)
     uint32_t index_tbl_num_entries = RCLASS_EXT(klass)->max_iv_count;
 
     size_t size;
-    bool embed = true;
 #if USE_RVARGC
     size = rb_obj_embedded_size(index_tbl_num_entries);
     if (!rb_gc_size_allocatable_p(size)) {
         size = sizeof(struct RObject);
-        embed = false;
     }
 #else
     size = sizeof(struct RObject);
-    if (index_tbl_num_entries > ROBJECT_EMBED_LEN_MAX) {
-        embed = false;
-    }
 #endif
 
-#if USE_RVARGC
     VALUE obj = newobj_of(klass, flags, 0, 0, 0, wb_protected, size);
-#else
-    VALUE obj = newobj_of(klass, flags, Qundef, Qundef, Qundef, wb_protected, size);
-#endif
 
-    if (embed) {
 #if USE_RVARGC
-        uint32_t capa = (uint32_t)((rb_gc_obj_slot_size(obj) - offsetof(struct RObject, as.ary)) / sizeof(VALUE));
-        GC_ASSERT(capa >= index_tbl_num_entries);
-
-        ROBJECT(obj)->numiv = capa;
-        for (size_t i = 0; i < capa; i++) {
-            ROBJECT(obj)->as.ary[i] = Qundef;
-        }
+    uint32_t capa = (uint32_t)((rb_gc_obj_slot_size(obj) - offsetof(struct RObject, as.ary)) / sizeof(VALUE));
+    ROBJECT(obj)->numiv = capa;
 #endif
+
+#if RUBY_DEBUG
+    VALUE *ptr = ROBJECT_IVPTR(obj);
+    for (size_t i = 0; i < ROBJECT_NUMIV(obj); i++) {
+        ptr[i] = Qundef;
     }
-    else {
-        rb_ensure_iv_list_size(obj, 0, index_tbl_num_entries);
-    }
+#endif
 
     return obj;
 }
@@ -10032,11 +10020,6 @@ gc_ref_update_object(rb_objspace_t *objspace, VALUE v)
 
         uint32_t capa = (uint32_t)((slot_size - offsetof(struct RObject, as.ary)) / sizeof(VALUE));
         ROBJECT(v)->numiv = capa;
-
-        // Fill end with Qundef
-        for (uint32_t i = numiv; i < capa; i++) {
-            ptr[i] = Qundef;
-        }
     }
 #endif
 

variable.c

@@ -1404,9 +1404,6 @@ rb_ensure_iv_list_size(VALUE obj, uint32_t len, uint32_t newsize)
         newptr = obj_ivar_heap_realloc(obj, len, newsize);
     }
 
-    for (; len < newsize; len++) {
-        newptr[len] = Qundef;
-    }
 #if USE_RVARGC
     ROBJECT(obj)->numiv = newsize;
 #else