Rename iv_count on shapes to next_iv_index

`iv_count` is a misleading name because when IVs are unset, the new
shape doesn't decrement this value. `next_iv_count` is an accurate, and
more descriptive name.

gc.c

@@ -3434,7 +3434,7 @@ obj_free(rb_objspace_t *objspace, VALUE obj)
                 VALUE klass = RBASIC_CLASS(obj);
 
                 // Increment max_iv_count if applicable, used to determine size pool allocation
-                uint32_t num_of_ivs = shape->iv_count;
+                uint32_t num_of_ivs = shape->next_iv_index;
                 if (RCLASS_EXT(klass)->max_iv_count < num_of_ivs) {
                     RCLASS_EXT(klass)->max_iv_count = num_of_ivs;
                 }

mjit_c.rb

@@ -606,7 +606,7 @@ module RubyVM::MJIT
       "rb_shape", Primitive.cexpr!("SIZEOF(struct rb_shape)"),
       edges: [CType::Pointer.new { self.rb_id_table }, Primitive.cexpr!("OFFSETOF((*((struct rb_shape *)NULL)), edges)")],
       edge_name: [self.ID, Primitive.cexpr!("OFFSETOF((*((struct rb_shape *)NULL)), edge_name)")],
-      iv_count: [self.attr_index_t, Primitive.cexpr!("OFFSETOF((*((struct rb_shape *)NULL)), iv_count)")],
+      next_iv_index: [self.attr_index_t, Primitive.cexpr!("OFFSETOF((*((struct rb_shape *)NULL)), next_iv_index)")],
       type: [CType::Immediate.parse("uint8_t"), Primitive.cexpr!("OFFSETOF((*((struct rb_shape *)NULL)), type)")],
       parent_id: [self.shape_id_t, Primitive.cexpr!("OFFSETOF((*((struct rb_shape *)NULL)), parent_id)")],
     )

shape.c

@@ -142,19 +142,19 @@ get_next_shape_internal(rb_shape_t* shape, ID id, VALUE obj, enum shape_type sha
 
                 switch (shape_type) {
                   case SHAPE_IVAR:
-                    new_shape->iv_count = rb_shape_get_shape_by_id(new_shape->parent_id)->iv_count + 1;
+                    new_shape->next_iv_index = rb_shape_get_shape_by_id(new_shape->parent_id)->next_iv_index + 1;
 
-                    // Check if we should update max_iv_count on the object's class
+                    // Check if we should update next_iv_index on the object's class
                     if (BUILTIN_TYPE(obj) == T_OBJECT) {
                         VALUE klass = rb_obj_class(obj);
-                        if (new_shape->iv_count > RCLASS_EXT(klass)->max_iv_count) {
-                            RCLASS_EXT(klass)->max_iv_count = new_shape->iv_count;
+                        if (new_shape->next_iv_index > RCLASS_EXT(klass)->max_iv_count) {
+                            RCLASS_EXT(klass)->max_iv_count = new_shape->next_iv_index;
                         }
                     }
                     break;
                   case SHAPE_IVAR_UNDEF:
                   case SHAPE_FROZEN:
-                    new_shape->iv_count = rb_shape_get_shape_by_id(new_shape->parent_id)->iv_count;
+                    new_shape->next_iv_index = rb_shape_get_shape_by_id(new_shape->parent_id)->next_iv_index;
                     break;
                   case SHAPE_ROOT:
                     rb_bug("Unreachable");
@@ -244,8 +244,8 @@ rb_shape_get_iv_index(rb_shape_t * shape, ID id, attr_index_t *value)
 
             switch (shape_type) {
               case SHAPE_IVAR:
-                RUBY_ASSERT(shape->iv_count > 0);
-                *value = shape->iv_count - 1;
+                RUBY_ASSERT(shape->next_iv_index > 0);
+                *value = shape->next_iv_index - 1;
                 return true;
               case SHAPE_IVAR_UNDEF:
               case SHAPE_ROOT:
@@ -280,7 +280,7 @@ rb_shape_alloc_with_parent_id(ID edge_name, shape_id_t parent_id)
     rb_shape_t * shape = shape_alloc();
 
     shape->edge_name = edge_name;
-    shape->iv_count = 0;
+    shape->next_iv_index = 0;
     shape->parent_id = parent_id;
 
     return shape;
@@ -404,12 +404,12 @@ rb_shape_edge_name(VALUE self)
 }
 
 static VALUE
-rb_shape_iv_count(VALUE self)
+rb_shape_next_iv_index(VALUE self)
 {
     rb_shape_t* shape;
     TypedData_Get_Struct(self, rb_shape_t, &shape_data_type, shape);
 
-    return INT2NUM(shape->iv_count);
+    return INT2NUM(shape->next_iv_index);
 }
 
 static VALUE
@@ -526,7 +526,7 @@ Init_shape(void)
     rb_define_method(rb_cShape, "parent", rb_shape_parent, 0);
     rb_define_method(rb_cShape, "edges", rb_shape_edges, 0);
     rb_define_method(rb_cShape, "edge_name", rb_shape_edge_name, 0);
-    rb_define_method(rb_cShape, "iv_count", rb_shape_iv_count, 0);
+    rb_define_method(rb_cShape, "next_iv_index", rb_shape_next_iv_index, 0);
     rb_define_method(rb_cShape, "depth", rb_shape_export_depth, 0);
     rb_define_method(rb_cShape, "id", rb_wrapped_shape_id, 0);
     rb_define_method(rb_cShape, "type", rb_shape_type, 0);

shape.h

@@ -45,7 +45,7 @@ typedef uint16_t shape_id_t;
 struct rb_shape {
     struct rb_id_table * edges; // id_table from ID (ivar) to next shape
     ID edge_name; // ID (ivar) for transition from parent to rb_shape
-    attr_index_t iv_count;
+    attr_index_t next_iv_index;
     uint8_t type;
     shape_id_t parent_id;
 };
@@ -129,7 +129,7 @@ static inline uint32_t
 ROBJECT_IV_COUNT(VALUE obj)
 {
     RBIMPL_ASSERT_TYPE(obj, RUBY_T_OBJECT);
-    uint32_t ivc = rb_shape_get_shape_by_id(ROBJECT_SHAPE_ID(obj))->iv_count;
+    uint32_t ivc = rb_shape_get_shape_by_id(ROBJECT_SHAPE_ID(obj))->next_iv_index;
     RUBY_ASSERT(ivc <= ROBJECT_NUMIV(obj));
     return ivc;
 }

test/ruby/test_shapes.rb

@@ -65,25 +65,25 @@ class TestShapes < Test::Unit::TestCase
   def test_iv_index
     example = RemoveAndAdd.new
     shape = RubyVM::Shape.of(example)
-    assert_equal 0, shape.iv_count
+    assert_equal 0, shape.next_iv_index
 
     example.add_foo # makes a transition
     new_shape = RubyVM::Shape.of(example)
     assert_equal([:@foo], example.instance_variables)
     assert_equal(shape.id, new_shape.parent.id)
-    assert_equal(1, new_shape.iv_count)
+    assert_equal(1, new_shape.next_iv_index)
 
     example.remove # makes a transition
     remove_shape = RubyVM::Shape.of(example)
     assert_equal([], example.instance_variables)
     assert_equal(new_shape.id, remove_shape.parent.id)
-    assert_equal(1, remove_shape.iv_count)
+    assert_equal(1, remove_shape.next_iv_index)
 
     example.add_bar # makes a transition
     bar_shape = RubyVM::Shape.of(example)
     assert_equal([:@bar], example.instance_variables)
     assert_equal(remove_shape.id, bar_shape.parent.id)
-    assert_equal(2, bar_shape.iv_count)
+    assert_equal(2, bar_shape.next_iv_index)
   end
 
   def test_new_obj_has_root_shape

variable.c

@@ -1018,7 +1018,7 @@ generic_ivar_update(st_data_t *k, st_data_t *v, st_data_t u, int existing)
         }
     }
     FL_SET((VALUE)*k, FL_EXIVAR);
-    ivtbl = gen_ivtbl_resize(ivtbl, ivup->shape->iv_count);
+    ivtbl = gen_ivtbl_resize(ivtbl, ivup->shape->next_iv_index);
     // Reinsert in to the hash table because ivtbl might be a newly resized chunk of memory
     *v = (st_data_t)ivtbl;
     ivup->ivtbl = ivtbl;
@@ -1435,7 +1435,7 @@ rb_ensure_generic_iv_list_size(VALUE obj, uint32_t newsize)
 void
 rb_init_iv_list(VALUE obj)
 {
-    uint32_t newsize = (uint32_t)(rb_shape_get_shape(obj)->iv_count * 2.0);
+    uint32_t newsize = (uint32_t)(rb_shape_get_shape(obj)->next_iv_index * 2.0);
     uint32_t len = ROBJECT_NUMIV(obj);
     rb_ensure_iv_list_size(obj, len, newsize < len ? len : newsize);
 }
@@ -1450,7 +1450,7 @@ obj_ivar_set(VALUE obj, ID id, VALUE val)
 
     if (!rb_shape_get_iv_index(shape, id, &index)) {
         shape = rb_shape_get_next(shape, obj, id);
-        index = shape->iv_count - 1;
+        index = shape->next_iv_index - 1;
     }
 
     uint32_t len = ROBJECT_NUMIV(obj);
@@ -1615,7 +1615,7 @@ iterate_over_shapes_with_callback(rb_shape_t *shape, VALUE* iv_list, rb_ivar_for
             return;
         case SHAPE_IVAR:
             iterate_over_shapes_with_callback(rb_shape_get_shape_by_id(shape->parent_id), iv_list, callback, arg);
-            VALUE val = iv_list[shape->iv_count - 1];
+            VALUE val = iv_list[shape->next_iv_index - 1];
             if (val != Qundef) {
                 callback(shape->edge_name, val, arg);
             }
@@ -1753,7 +1753,7 @@ rb_ivar_count(VALUE obj)
 
     switch (BUILTIN_TYPE(obj)) {
       case T_OBJECT:
-        if (rb_shape_get_shape(obj)->iv_count > 0) {
+        if (rb_shape_get_shape(obj)->next_iv_index > 0) {
             st_index_t i, count, num = ROBJECT_IV_COUNT(obj);
             const VALUE *const ivptr = ROBJECT_IVPTR(obj);
             for (i = count = 0; i < num; ++i) {

yjit/src/cruby_bindings.inc.rs

@@ -419,7 +419,7 @@ pub type shape_id_t = u32;
 pub struct rb_shape {
     pub edges: *mut rb_id_table,
     pub edge_name: ID,
-    pub iv_count: attr_index_t,
+    pub next_iv_index: attr_index_t,
     pub type_: u8,
     pub parent_id: shape_id_t,
 }