Get rid of RSHAPE_PARENT in favor of RSHAPE_DIRECT_CHILD_P

`RSHAPE_PARENT` is error prone because it returns a raw untagged
shape_id.

To check if a shape is a direct parent of another, tags should be
discarded. So providing a comparison function is better than exposing
untagged ids.

Author: byroot

ext/objspace/objspace_dump.c

@@ -801,7 +801,7 @@ shape_id_i(shape_id_t shape_id, void *data)
 
     if (RSHAPE_TYPE(shape_id) != SHAPE_ROOT) {
         dump_append(dc, ", \"parent_id\":");
-        dump_append_lu(dc, RSHAPE_PARENT(shape_id));
+        dump_append_lu(dc, RSHAPE_PARENT_RAW_ID(shape_id));
     }
 
     dump_append(dc, ", \"depth\":");

shape.h

@@ -271,11 +271,17 @@ rb_shape_root(size_t heap_id)
 }
 
 static inline shape_id_t
-RSHAPE_PARENT(shape_id_t shape_id)
+RSHAPE_PARENT_RAW_ID(shape_id_t shape_id)
 {
     return RSHAPE(shape_id)->parent_id;
 }
 
+static inline bool
+RSHAPE_DIRECT_CHILD_P(shape_id_t parent_id, shape_id_t child_id)
+{
+    return RSHAPE(child_id)->parent_id == (parent_id & SHAPE_ID_OFFSET_MASK);
+}
+
 static inline enum shape_type
 RSHAPE_TYPE(shape_id_t shape_id)
 {

vm_insnhelper.c

@@ -1473,7 +1473,7 @@ vm_setivar_default(VALUE obj, ID id, VALUE val, shape_id_t dest_shape_id, attr_i
         RUBY_ASSERT(dest_shape_id != INVALID_SHAPE_ID && shape_id != INVALID_SHAPE_ID);
     }
     else if (dest_shape_id != INVALID_SHAPE_ID) {
-        if (shape_id == RSHAPE_PARENT(dest_shape_id) && RSHAPE_EDGE_NAME(dest_shape_id) == id && RSHAPE_CAPACITY(shape_id) == RSHAPE_CAPACITY(dest_shape_id)) {
+        if (RSHAPE_DIRECT_CHILD_P(shape_id, dest_shape_id) && RSHAPE_EDGE_NAME(dest_shape_id) == id && RSHAPE_CAPACITY(shape_id) == RSHAPE_CAPACITY(dest_shape_id)) {
             RUBY_ASSERT(index < RSHAPE_CAPACITY(dest_shape_id));
         }
         else {
@@ -1514,14 +1514,11 @@ vm_setivar(VALUE obj, ID id, VALUE val, shape_id_t dest_shape_id, attr_index_t i
                 VM_ASSERT(!rb_ractor_shareable_p(obj));
             }
             else if (dest_shape_id != INVALID_SHAPE_ID) {
-                shape_id_t source_shape_id = RSHAPE_PARENT(dest_shape_id);
-
-                if (shape_id == source_shape_id && RSHAPE_EDGE_NAME(dest_shape_id) == id && RSHAPE_CAPACITY(shape_id) == RSHAPE_CAPACITY(dest_shape_id)) {
+                if (RSHAPE_DIRECT_CHILD_P(shape_id, dest_shape_id) && RSHAPE_EDGE_NAME(dest_shape_id) == id && RSHAPE_CAPACITY(shape_id) == RSHAPE_CAPACITY(dest_shape_id)) {
                     RUBY_ASSERT(dest_shape_id != INVALID_SHAPE_ID && shape_id != INVALID_SHAPE_ID);
 
                     RBASIC_SET_SHAPE_ID(obj, dest_shape_id);
 
-                    RUBY_ASSERT(rb_shape_get_next_iv_shape(source_shape_id, id) == dest_shape_id);
                     RUBY_ASSERT(index < RSHAPE_CAPACITY(dest_shape_id));
                 }
                 else {