From 10788166e7e568fdcd0b748e8d5dab442dcdc7ef Mon Sep 17 00:00:00 2001
From: Aaron Patterson <tenderlove@ruby-lang.org>
Date: Thu, 17 Nov 2022 15:57:11 -0800
Subject: Differentiate T_OBJECT shapes from other objects

We would like to differentiate types of objects via their shape.  This
commit adds a special T_OBJECT shape when we allocate an instance of
T_OBJECT.  This allows us to avoid testing whether an object is an
instance of a T_OBJECT or not, we can just check the shape.
---
 shape.c | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

(limited to 'shape.c')

diff --git a/shape.c b/shape.c
index bb51abecbf..d98e596eb1 100644
--- a/shape.c
+++ b/shape.c
@@ -8,6 +8,7 @@
 #include <stdbool.h>
 
 static ID id_frozen;
+static ID id_t_object;
 static ID size_pool_edge_names[SIZE_POOL_COUNT];
 
 /*
@@ -152,6 +153,7 @@ get_next_shape_internal(rb_shape_t * shape, ID id, enum shape_type shape_type)
                   case SHAPE_CAPACITY_CHANGE:
                   case SHAPE_IVAR_UNDEF:
                   case SHAPE_FROZEN:
+                  case SHAPE_T_OBJECT:
                     new_shape->next_iv_index = shape->next_iv_index;
                     break;
                   case SHAPE_INITIAL_CAPACITY:
@@ -264,6 +266,7 @@ rb_shape_get_iv_index(rb_shape_t * shape, ID id, attr_index_t *value)
               case SHAPE_IVAR_UNDEF:
               case SHAPE_ROOT:
               case SHAPE_INITIAL_CAPACITY:
+              case SHAPE_T_OBJECT:
                 return false;
               case SHAPE_FROZEN:
                 rb_bug("Ivar should not exist on transition\n");
@@ -333,14 +336,16 @@ rb_shape_rebuild_shape(rb_shape_t * initial_shape, rb_shape_t * dest_shape)
 {
     rb_shape_t * midway_shape;
 
-    if (dest_shape->type != SHAPE_ROOT) {
+    RUBY_ASSERT(initial_shape->type == SHAPE_T_OBJECT);
+
+    if (dest_shape->type != initial_shape->type) {
         midway_shape = rb_shape_rebuild_shape(initial_shape, rb_shape_get_parent(dest_shape));
     }
     else {
         midway_shape = initial_shape;
     }
 
-    switch (dest_shape->type) {
+    switch ((enum shape_type)dest_shape->type) {
       case SHAPE_IVAR:
         if (midway_shape->capacity <= midway_shape->next_iv_index) {
             // There isn't enough room to write this IV, so we need to increase the capacity
@@ -355,6 +360,8 @@ rb_shape_rebuild_shape(rb_shape_t * initial_shape, rb_shape_t * dest_shape)
       case SHAPE_ROOT:
       case SHAPE_FROZEN:
       case SHAPE_CAPACITY_CHANGE:
+      case SHAPE_INITIAL_CAPACITY:
+      case SHAPE_T_OBJECT:
         break;
     }
 
@@ -592,6 +599,7 @@ void
 Init_default_shapes(void)
 {
     id_frozen = rb_make_internal_id();
+    id_t_object = rb_make_internal_id();
 
     // Shapes by size pool
     for (int i = 0; i < SIZE_POOL_COUNT; i++) {
@@ -615,6 +623,16 @@ Init_default_shapes(void)
         RUBY_ASSERT(rb_shape_id(new_shape) == (shape_id_t)i);
     }
 
+    // Make shapes for T_OBJECT
+    for (int i = 0; i < SIZE_POOL_COUNT; i++) {
+        rb_shape_t * shape = rb_shape_get_shape_by_id(i);
+#if RUBY_DEBUG
+        rb_shape_t * t_object_shape =
+#endif
+            get_next_shape_internal(shape, id_t_object, SHAPE_T_OBJECT);
+        RUBY_ASSERT(rb_shape_id(t_object_shape) == (shape_id_t)(i + SIZE_POOL_COUNT));
+    }
+
     // Special const shape
 #if RUBY_DEBUG
     rb_shape_t * special_const_shape =
@@ -644,6 +662,7 @@ Init_shape(void)
     rb_define_method(rb_cShape, "capacity", rb_shape_capacity, 0);
     rb_define_const(rb_cShape, "SHAPE_ROOT", INT2NUM(SHAPE_ROOT));
     rb_define_const(rb_cShape, "SHAPE_IVAR", INT2NUM(SHAPE_IVAR));
+    rb_define_const(rb_cShape, "SHAPE_T_OBJECT", INT2NUM(SHAPE_T_OBJECT));
     rb_define_const(rb_cShape, "SHAPE_IVAR_UNDEF", INT2NUM(SHAPE_IVAR_UNDEF));
     rb_define_const(rb_cShape, "SHAPE_FROZEN", INT2NUM(SHAPE_FROZEN));
     rb_define_const(rb_cShape, "SHAPE_BITS", INT2NUM(SHAPE_BITS));
-- 
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