Revert "Reserve 2 bits for expressing object layout (#17139)"HEADmaster

This reverts commit 63d9f090b5d9461cf0b9446e0039d9c56156b826.

14 files changed, 44 insertions, 216 deletions

diff --git a/array.c b/array.c
index 7f06e3c9c7..08d8d17c90 100644
--- a/array.c
+++ b/array.c
@@ -30,7 +30,6 @@
 #include "ruby/thread.h"
 #include "ruby/util.h"
 #include "ruby/ractor.h"
-#include "shape.h"
 #include "vm_core.h"
 #include "builtin.h"
 
@@ -910,7 +909,6 @@ init_fake_ary_flags(void)
     struct RArray fake_ary = {0};
     fake_ary.basic.flags = T_ARRAY;
     VALUE ary = (VALUE)&fake_ary;
-    RBASIC_SET_SHAPE_ID(ary, ROOT_SHAPE_ID | SHAPE_ID_LAYOUT_OTHER);
     rb_ary_freeze(ary);
     return fake_ary.basic.flags;
 }
diff --git a/class.c b/class.c
index 02078cc9bc..69194ccab2 100644
--- a/class.c
+++ b/class.c
@@ -585,15 +585,7 @@ class_alloc0(enum ruby_value_type type, VALUE klass, bool boxable)
     VALUE flags = type | FL_SHAREABLE;
     if (boxable) flags |= RCLASS_BOXABLE;
 
-    shape_id_t shape_id = ROOT_SHAPE_ID;
-    if (boxable) {
-        shape_id |= SHAPE_ID_LAYOUT_OTHER;
-    }
-    else {
-        shape_id |= SHAPE_ID_LAYOUT_RCLASS;
-    }
-
-    struct RClass *obj = (struct RClass *)rb_newobj(GET_EC(), klass, flags, shape_id, true, alloc_size);
+    NEWOBJ_OF(obj, struct RClass, klass, flags, alloc_size);
 
     obj->object_id = 0;
 
diff --git a/depend b/depend
index a2e8312298..e61b685670 100644
--- a/depend
+++ b/depend
@@ -80,7 +80,6 @@ array.$(OBJEXT): $(top_srcdir)/internal/sanitizers.h
 array.$(OBJEXT): $(top_srcdir)/internal/serial.h
 array.$(OBJEXT): $(top_srcdir)/internal/set_table.h
 array.$(OBJEXT): $(top_srcdir)/internal/static_assert.h
-array.$(OBJEXT): $(top_srcdir)/internal/struct.h
 array.$(OBJEXT): $(top_srcdir)/internal/variable.h
 array.$(OBJEXT): $(top_srcdir)/internal/vm.h
 array.$(OBJEXT): $(top_srcdir)/internal/warnings.h
diff --git a/gc.c b/gc.c
index 6357577e63..9eb7232940 100644
--- a/gc.c
+++ b/gc.c
@@ -1056,15 +1056,7 @@ rb_newobj(rb_execution_context_t *ec, VALUE klass, VALUE flags, shape_id_t shape
 VALUE
 rb_ec_newobj_of(rb_execution_context_t *ec, VALUE klass, VALUE flags, size_t size)
 {
-    VALUE type = flags & T_MASK;
-    RUBY_ASSERT(type != T_OBJECT);
-    RUBY_ASSERT(type != T_DATA);
-    RUBY_ASSERT(type != T_CLASS);
-    RUBY_ASSERT(type != T_MODULE);
-    RUBY_ASSERT(type != T_ICLASS);
-    (void)type;
-
-    return rb_newobj(ec, klass, flags, ROOT_SHAPE_ID | SHAPE_ID_LAYOUT_OTHER, true, size);
+    return rb_newobj(ec, klass, flags, ROOT_SHAPE_ID, true, size);
 }
 
 VALUE
@@ -1076,13 +1068,13 @@ rb_newobj_of_with_shape(VALUE klass, VALUE flags, shape_id_t shape_id, size_t si
 VALUE
 rb_newobj_of(VALUE klass, VALUE flags, size_t size)
 {
-    return rb_newobj(GET_EC(), klass, flags, ROOT_SHAPE_ID | SHAPE_ID_LAYOUT_OTHER, true, size);
+    return rb_newobj(GET_EC(), klass, flags, ROOT_SHAPE_ID, true, size);
 }
 
 static
 VALUE class_allocate_complex_instance(VALUE klass, uint32_t capacity)
 {
-    shape_id_t initial_shape_id = rb_shape_id_with_robject_layout(rb_shape_root(rb_gc_heap_id_for_size(sizeof(struct RObject))));
+    shape_id_t initial_shape_id = rb_shape_root(rb_gc_heap_id_for_size(sizeof(struct RObject)));
     VALUE obj = rb_newobj_of_with_shape(klass, T_OBJECT, initial_shape_id, sizeof(struct RObject));
     rb_obj_init_complex(obj, rb_st_init_numtable_with_size(capacity));
     return obj;
@@ -1107,7 +1099,7 @@ rb_class_allocate_instance(VALUE klass)
 
         // There might be a NEWOBJ tracepoint callback, and it may set fields.
         // So the shape must be passed to `NEWOBJ_OF`.
-        obj = rb_newobj_of_with_shape(klass, T_OBJECT, rb_shape_id_with_robject_layout(rb_shape_root(rb_gc_heap_id_for_size(size))), size);
+        obj = rb_newobj_of_with_shape(klass, T_OBJECT, rb_shape_root(rb_gc_heap_id_for_size(size)), size);
 
         #if RUBY_DEBUG
             VALUE *ptr = ROBJECT_FIELDS(obj);
@@ -1157,7 +1149,7 @@ typed_data_alloc(VALUE klass, VALUE typed_flag, void *datap, const rb_data_type_
     RBIMPL_NONNULL_ARG(type);
     if (klass) rb_data_object_check(klass);
     bool wb_protected = (type->flags & RUBY_FL_WB_PROTECTED) || !type->function.dmark;
-    VALUE obj = rb_newobj(GET_EC(), klass, T_DATA, ROOT_SHAPE_ID | SHAPE_ID_LAYOUT_RDATA, wb_protected, size);
+    VALUE obj = rb_newobj(GET_EC(), klass, T_DATA, ROOT_SHAPE_ID, wb_protected, size);
 
     rb_gc_register_pinning_obj(obj);
 
@@ -4197,11 +4189,7 @@ vm_weak_table_gen_fields_foreach(st_data_t key, st_data_t value, st_data_t data)
         break;
 
       case ST_DELETE:
-        // When we're removing an object from the weak ref table, we need to
-        // set the shape on it so that the GC finalizer won't try to remove
-        // it again.  A "root shape" indicates to the GC that this object
-        // has no fields on it, hence it won't be in the gen fields table.
-        RBASIC_SET_SHAPE_ID((VALUE)key, ROOT_SHAPE_ID | SHAPE_ID_LAYOUT_OTHER);
+        RBASIC_SET_SHAPE_ID((VALUE)key, ROOT_SHAPE_ID);
         return ST_DELETE;
 
       case ST_REPLACE: {
diff --git a/imemo.c b/imemo.c
index 796e078c89..3448a8dcd3 100644
--- a/imemo.c
+++ b/imemo.c
@@ -141,11 +141,7 @@ rb_imemo_fields_new(VALUE owner, shape_id_t shape_id, bool shareable)
     size_t embedded_size = offsetof(struct rb_fields, as.embed) + capa * sizeof(VALUE);
     RUBY_ASSERT(rb_gc_size_allocatable_p(embedded_size));
     VALUE fields = rb_imemo_new(imemo_fields, owner, embedded_size, shareable);
-    // imemo fields objects should always have "RObject" layout.  The
-    // layout in the shape describes the layout of the thing on which it is set.
-    // Imemo fields have the same layout as robject, therefore the layout
-    // should reflect that fact.
-    RBASIC_SET_SHAPE_ID(fields, rb_shape_id_with_robject_layout(shape_id));
+    RBASIC_SET_SHAPE_ID(fields, shape_id);
     RUBY_ASSERT(IMEMO_TYPE_P(fields, imemo_fields));
     return fields;
 }
@@ -156,11 +152,7 @@ rb_imemo_fields_new_complex(VALUE owner, shape_id_t shape_id, size_t capa, bool
     VALUE fields = rb_imemo_new(imemo_fields, owner, sizeof(struct rb_fields), shareable);
     IMEMO_OBJ_FIELDS(fields)->as.complex.table = st_init_numtable_with_size(capa);
     FL_SET_RAW(fields, OBJ_FIELD_HEAP);
-    // imemo fields objects should always have "RObject" layout.  The
-    // layout in the shape describes the layout of the thing on which it is set.
-    // Imemo fields have the same layout as robject, therefore the layout
-    // should reflect that fact.
-    RBASIC_SET_SHAPE_ID(fields, rb_shape_id_with_robject_layout(shape_id));
+    RBASIC_SET_SHAPE_ID(fields, shape_id);
     return fields;
 }
 
@@ -185,11 +177,7 @@ rb_imemo_fields_new_complex_tbl(VALUE owner, shape_id_t shape_id, st_table *tbl,
     VALUE fields = rb_imemo_new(imemo_fields, owner, sizeof(struct rb_fields), shareable);
     IMEMO_OBJ_FIELDS(fields)->as.complex.table = tbl;
     FL_SET_RAW(fields, OBJ_FIELD_HEAP);
-    // imemo fields objects should always have "RObject" layout.  The
-    // layout in the shape describes the layout of the thing on which it is set.
-    // Imemo fields have the same layout as robject, therefore the layout
-    // should reflect that fact.
-    RBASIC_SET_SHAPE_ID(fields, rb_shape_id_with_robject_layout(shape_id));
+    RBASIC_SET_SHAPE_ID(fields, shape_id);
     st_foreach(tbl, imemo_fields_trigger_wb_i, (st_data_t)fields);
     return fields;
 }
diff --git a/internal/gc.h b/internal/gc.h
index b78808370c..41675810c7 100644
--- a/internal/gc.h
+++ b/internal/gc.h
@@ -124,7 +124,7 @@ struct rb_objspace; /* in vm_core.h */
     T *(var) = (T *)rb_ec_newobj_of((ec), (c), (f), s)
 #define NEWOBJ_OF(var, T, c, f, s) EC_NEWOBJ_OF(var, T, c, f, s, GET_EC())
 #define UNPROTECTED_NEWOBJ_OF(var, T, c, f, s) \
-    T *(var) = (T *)rb_newobj((GET_EC()), (c), (f), ROOT_SHAPE_ID | SHAPE_ID_LAYOUT_OTHER, false, s)
+    T *(var) = (T *)rb_newobj((GET_EC()), (c), (f), 0 /* ROOT_SHAPE_ID */, false, s)
 
 #ifndef RB_GC_OBJECT_METADATA_ENTRY_DEFINED
 # define RB_GC_OBJECT_METADATA_ENTRY_DEFINED
diff --git a/ractor.c b/ractor.c
index f94c06cc73..d611ca97c2 100644
--- a/ractor.c
+++ b/ractor.c
@@ -2015,7 +2015,7 @@ move_enter(VALUE obj, struct obj_traverse_replace_data *data)
     else {
         VALUE type = RB_BUILTIN_TYPE(obj);
         size_t slot_size = rb_gc_obj_slot_size(obj);
-        VALUE moved = rb_newobj(GET_EC(), 0, type, RBASIC_SHAPE_ID(obj), wb_protected_types[type], slot_size);
+        VALUE moved = rb_newobj(GET_EC(), 0, type, 0, wb_protected_types[type], slot_size);
         MEMZERO(((struct RBasic *)moved) + 1, char, slot_size - sizeof(struct RBasic));
         data->replacement = (VALUE)moved;
         return traverse_cont;
diff --git a/shape.c b/shape.c
index 7a02b23073..24f1394f6c 100644
--- a/shape.c
+++ b/shape.c
@@ -409,14 +409,10 @@ rb_obj_shape_id(VALUE obj)
 
     if (BUILTIN_TYPE(obj) == T_CLASS || BUILTIN_TYPE(obj) == T_MODULE) {
         VALUE fields_obj = RCLASS_WRITABLE_FIELDS_OBJ(obj);
-        shape_id_t base = ROOT_SHAPE_ID;
         if (fields_obj) {
-            // Remove the layout from the fields object.  We want to
-            // combine the shape of the fields object with the layout of the
-            // class / module object.
-            base = RBASIC_SHAPE_ID(fields_obj) & ~SHAPE_ID_LAYOUT_MASK;
+            return RBASIC_SHAPE_ID(fields_obj);
         }
-        return rb_shape_layout(RBASIC_SHAPE_ID(obj)) | base;
+        return ROOT_SHAPE_ID;
     }
     return RBASIC_SHAPE_ID(obj);
 }
@@ -701,7 +697,7 @@ rb_shape_transition_object_id(shape_id_t original_shape_id)
     bool dont_care;
     rb_shape_t *shape = get_next_shape_internal(RSHAPE(original_shape_id), id_object_id, SHAPE_OBJ_ID, &dont_care, true);
     if (!shape) {
-        return rb_shape_layout(original_shape_id) | ROOT_COMPLEX_WITH_OBJ_ID | RSHAPE_FLAGS(original_shape_id);
+        return ROOT_COMPLEX_WITH_OBJ_ID | RSHAPE_FLAGS(original_shape_id);
     }
 
     RUBY_ASSERT(shape);
@@ -1229,55 +1225,17 @@ rb_shape_foreach_field(shape_id_t initial_shape_id, rb_shape_foreach_transition_
 }
 
 #if RUBY_DEBUG
-/*
- * Get the layout of this object.  The "layout" indicates what strategy
- * we should use for fetching instance variables from `obj`.  It's based
- * on the C struct layout for each particular object.
- *
- * TODO: make Struct have a similar layout to RDATA
- */
-static shape_id_t
-rb_shape_expected_layout(VALUE obj)
-{
-    switch (BUILTIN_TYPE(obj)) {
-      case T_OBJECT:
-        return SHAPE_ID_LAYOUT_ROBJECT;
-      case T_CLASS:
-      case T_MODULE:
-        if (FL_TEST_RAW(obj, RCLASS_BOXABLE)) {
-            return SHAPE_ID_LAYOUT_OTHER;
-        }
-        return SHAPE_ID_LAYOUT_RCLASS;
-      case T_DATA:
-        return SHAPE_ID_LAYOUT_RDATA;
-      case T_IMEMO:
-        if (IMEMO_TYPE_P(obj, imemo_fields)) {
-            return SHAPE_ID_LAYOUT_ROBJECT;
-        }
-        return SHAPE_ID_LAYOUT_OTHER;
-      default:
-        return SHAPE_ID_LAYOUT_OTHER;
-    }
-}
-
 bool
 rb_shape_verify_consistency(VALUE obj, shape_id_t shape_id)
 {
-    if (shape_id == INVALID_SHAPE_ID) {
-        rb_bug("Can't set INVALID_SHAPE_ID on an object");
-    }
-
-    shape_id_t actual_layout = rb_shape_layout(rb_obj_shape_id(obj));
-    shape_id_t expected_layout = rb_shape_expected_layout(obj);
-    if (actual_layout != expected_layout) {
-        rb_bug("shape_id layout mismatch: expected=%x actual=%x shape_id=%u obj=%s",
-                expected_layout, actual_layout, shape_id, rb_obj_info(obj));
-    }
-
     if (shape_id == ROOT_SHAPE_ID) {
         return true;
     }
 
+    if (shape_id == INVALID_SHAPE_ID) {
+        rb_bug("Can't set INVALID_SHAPE_ID on an object");
+    }
+
     rb_shape_t *shape = RSHAPE(shape_id);
 
     bool has_object_id = false;
@@ -1291,11 +1249,13 @@ rb_shape_verify_consistency(VALUE obj, shape_id_t shape_id)
 
     if (rb_shape_has_object_id(shape_id)) {
         if (!has_object_id) {
+            rb_p(obj);
             rb_bug("shape_id claim having obj_id but doesn't shape_id=%u, obj=%s", shape_id, rb_obj_info(obj));
         }
     }
     else {
         if (has_object_id) {
+            rb_p(obj);
             rb_bug("shape_id claim not having obj_id but it does shape_id=%u, obj=%s", shape_id, rb_obj_info(obj));
         }
     }
@@ -1370,25 +1330,6 @@ shape_has_object_id_p(VALUE self)
 }
 
 static VALUE
-shape_layout(VALUE self)
-{
-    shape_id_t shape_id = NUM2UINT(rb_struct_getmember(self, rb_intern("id")));
-
-    switch (rb_shape_layout(shape_id)) {
-      case SHAPE_ID_LAYOUT_ROBJECT:
-        return ID2SYM(rb_intern("robject"));
-      case SHAPE_ID_LAYOUT_RCLASS:
-        return ID2SYM(rb_intern("rclass"));
-      case SHAPE_ID_LAYOUT_RDATA:
-        return ID2SYM(rb_intern("rdata"));
-      case SHAPE_ID_LAYOUT_OTHER:
-        return ID2SYM(rb_intern("other"));
-      default:
-        rb_bug("unknown shape layout: %u", rb_shape_layout(shape_id));
-    }
-}
-
-static VALUE
 parse_key(ID key)
 {
     if (is_instance_id(key)) {
@@ -1687,7 +1628,6 @@ Init_shape(void)
     rb_define_method(rb_cShape, "complex?", shape_complex, 0);
     rb_define_method(rb_cShape, "shape_frozen?", shape_frozen, 0);
     rb_define_method(rb_cShape, "has_object_id?", shape_has_object_id_p, 0);
-    rb_define_method(rb_cShape, "layout", shape_layout, 0);
 
     rb_define_const(rb_cShape, "SHAPE_ROOT", INT2NUM(SHAPE_ROOT));
     rb_define_const(rb_cShape, "SHAPE_IVAR", INT2NUM(SHAPE_IVAR));
diff --git a/shape.h b/shape.h
index a319449988..61fadca5ba 100644
--- a/shape.h
+++ b/shape.h
@@ -27,14 +27,12 @@ STATIC_ASSERT(shape_id_num_bits, SHAPE_ID_NUM_BITS == sizeof(shape_id_t) * CHAR_
 //      19-22 SHAPE_ID_HEAP_INDEX_MASK
 //              index in rb_shape_tree.capacities. Allow to access slot size.
 //              Currently always 0 except for T_OBJECT.
-//      23 SHAPE_ID_FL_COMPLEX
-//              The object is backed by a `st_table`.
-//      24 SHAPE_ID_FL_FROZEN
+//      23 SHAPE_ID_FL_FROZEN
 //              Whether the object is frozen or not.
-//      25 SHAPE_ID_FL_HAS_OBJECT_ID
+//      24 SHAPE_ID_FL_HAS_OBJECT_ID
 //              Whether the object has an `SHAPE_OBJ_ID` transition.
-//      26-27 SHAPE_ID_LAYOUT_MASK
-//              The object's physical field layout.
+//      25 SHAPE_ID_FL_COMPLEX
+//              The object is backed by a `st_table`.
 
 enum shape_id_fl_type {
 #define RBIMPL_SHAPE_ID_FL(n) (1<<(SHAPE_ID_FL_USHIFT+n))
@@ -45,26 +43,8 @@ enum shape_id_fl_type {
     SHAPE_ID_FL_FROZEN = RBIMPL_SHAPE_ID_FL(1),
     SHAPE_ID_FL_HAS_OBJECT_ID = RBIMPL_SHAPE_ID_FL(2),
 
-    // Means IVs are found at an offset from the object's addr, or in a
-    // malloc allocated side table
-    SHAPE_ID_LAYOUT_ROBJECT = 0,
-
-    // Means this object is a class/module that is NOT RCLASS_BOXABLE, and IV's
-    // are found in the fields_obj found on the rclass struct
-    SHAPE_ID_LAYOUT_RCLASS = RBIMPL_SHAPE_ID_FL(3),
-
-    // Means this object is an RData or RTypedData and IVs are found in the
-    // fields_obj found on the RData/RTypedData struct
-    SHAPE_ID_LAYOUT_RDATA = RBIMPL_SHAPE_ID_FL(4),
-
-    // Means this is a complicated object: boxable classes, structs, objects
-    // that store IVs on the geniv table
-    SHAPE_ID_LAYOUT_OTHER = SHAPE_ID_LAYOUT_RCLASS | SHAPE_ID_LAYOUT_RDATA,
-
-    SHAPE_ID_LAYOUT_MASK = SHAPE_ID_LAYOUT_OTHER,
-
     SHAPE_ID_FL_NON_CANONICAL_MASK = SHAPE_ID_FL_FROZEN | SHAPE_ID_FL_HAS_OBJECT_ID,
-    SHAPE_ID_FLAGS_MASK = SHAPE_ID_HEAP_INDEX_MASK | SHAPE_ID_FL_NON_CANONICAL_MASK | SHAPE_ID_FL_COMPLEX | SHAPE_ID_LAYOUT_MASK,
+    SHAPE_ID_FLAGS_MASK = SHAPE_ID_HEAP_INDEX_MASK | SHAPE_ID_FL_NON_CANONICAL_MASK | SHAPE_ID_FL_COMPLEX,
 
 #undef RBIMPL_SHAPE_ID_FL
 };
@@ -75,13 +55,12 @@ enum shape_id_mask {
     SHAPE_ID_HAS_IVAR_MASK = SHAPE_ID_FL_COMPLEX | (SHAPE_ID_OFFSET_MASK - 1),
 };
 
-// The interpreter doesn't care about frozen status, slot size, or object id, and
-// has its own checks for physical field layout when reading ivars.
+// The interpreter doesn't care about frozen status, slot size or object id when reading ivars.
 // So we normalize shape_id by clearing these bits to improve cache hits.
 // JITs however might care about some of it.
-#define SHAPE_ID_READ_ONLY_MASK (~(SHAPE_ID_FL_FROZEN | SHAPE_ID_HEAP_INDEX_MASK | SHAPE_ID_FL_HAS_OBJECT_ID | SHAPE_ID_LAYOUT_MASK))
+#define SHAPE_ID_READ_ONLY_MASK (~(SHAPE_ID_FL_FROZEN | SHAPE_ID_HEAP_INDEX_MASK | SHAPE_ID_FL_HAS_OBJECT_ID))
 // For write it's the same idea, but here we do care about frozen status.
-#define SHAPE_ID_WRITE_MASK (~(SHAPE_ID_HEAP_INDEX_MASK | SHAPE_ID_FL_HAS_OBJECT_ID | SHAPE_ID_LAYOUT_MASK))
+#define SHAPE_ID_WRITE_MASK (~(SHAPE_ID_HEAP_INDEX_MASK | SHAPE_ID_FL_HAS_OBJECT_ID))
 
 typedef uint32_t redblack_id_t;
 
@@ -174,18 +153,11 @@ RBASIC_SET_SHAPE_ID_NO_CHECKS(VALUE obj, shape_id_t shape_id)
 #endif
 }
 
-static inline shape_id_t
-rb_shape_layout(shape_id_t shape_id)
-{
-    return shape_id & SHAPE_ID_LAYOUT_MASK;
-}
-
 static inline void
 RBASIC_SET_SHAPE_ID(VALUE obj, shape_id_t shape_id)
 {
     RUBY_ASSERT(!RB_SPECIAL_CONST_P(obj));
     RUBY_ASSERT(!RB_TYPE_P(obj, T_IMEMO) || IMEMO_TYPE_P(obj, imemo_fields));
-    RUBY_ASSERT(!IMEMO_TYPE_P(obj, imemo_fields) || rb_shape_layout(shape_id) == SHAPE_ID_LAYOUT_ROBJECT);
 
     RBASIC_SET_SHAPE_ID_NO_CHECKS(obj, shape_id);
 
@@ -260,12 +232,6 @@ rb_shape_canonical_p(shape_id_t shape_id)
     return !(shape_id & SHAPE_ID_FL_NON_CANONICAL_MASK);
 }
 
-static inline shape_id_t
-rb_shape_id_with_robject_layout(shape_id_t shape_id)
-{
-    return (shape_id & ~SHAPE_ID_LAYOUT_MASK) | SHAPE_ID_LAYOUT_ROBJECT;
-}
-
 static inline uint8_t
 rb_shape_heap_index(shape_id_t shape_id)
 {
@@ -484,10 +450,10 @@ rb_shape_transition_frozen(shape_id_t shape_id)
 static inline shape_id_t
 rb_shape_transition_complex(shape_id_t shape_id)
 {
-    shape_id_t next_shape_id = rb_shape_layout(shape_id) | ROOT_COMPLEX_SHAPE_ID;
+    shape_id_t next_shape_id = ROOT_COMPLEX_SHAPE_ID;
 
     if (rb_shape_has_object_id(shape_id)) {
-        next_shape_id = rb_shape_layout(shape_id) | ROOT_COMPLEX_WITH_OBJ_ID;
+        next_shape_id = ROOT_COMPLEX_WITH_OBJ_ID;
     }
 
     uint8_t heap_index = rb_shape_heap_index(shape_id);
diff --git a/string.c b/string.c
index 61d4f16679..6865b0d8e6 100644
--- a/string.c
+++ b/string.c
@@ -630,7 +630,7 @@ static VALUE
 setup_fake_str(struct RString *fake_str, const char *name, long len, int encidx)
 {
     fake_str->basic.flags = T_STRING|RSTRING_NOEMBED|STR_NOFREE|STR_FAKESTR;
-    RBASIC_SET_SHAPE_ID((VALUE)fake_str, ROOT_SHAPE_ID | SHAPE_ID_LAYOUT_OTHER);
+    RBASIC_SET_SHAPE_ID((VALUE)fake_str, ROOT_SHAPE_ID);
 
     if (!name) {
         RUBY_ASSERT_ALWAYS(len == 0);
diff --git a/test/ruby/test_shapes.rb b/test/ruby/test_shapes.rb
index bace69658a..ef5dbd9fb1 100644
--- a/test/ruby/test_shapes.rb
+++ b/test/ruby/test_shapes.rb
@@ -1067,37 +1067,6 @@ class TestShapes < Test::Unit::TestCase
     assert_nil shape.parent
   end
 
-  def test_shape_layout
-    assert_equal :robject, RubyVM::Shape.of(TestObject.new).layout
-
-    if ENV["RUBY_BOX"]
-      assert_equal :other, RubyVM::Shape.of(Kernel).layout
-      assert_equal :other, RubyVM::Shape.of(String).layout
-    else
-      assert_equal :rclass, RubyVM::Shape.of(Kernel).layout
-      assert_equal :rclass, RubyVM::Shape.of(String).layout
-    end
-
-    assert_equal :rclass, RubyVM::Shape.of(Class.new).layout
-    assert_equal :rclass, RubyVM::Shape.of(Module.new).layout
-
-    klass = Class.new
-    assert_equal :rclass, RubyVM::Shape.of(klass).layout
-    klass.instance_variable_set(:@a, 123)
-    assert_equal :rclass, RubyVM::Shape.of(klass).layout
-
-    assert_equal :rdata, RubyVM::Shape.of(Thread.current).layout
-    assert_equal :rdata, RubyVM::Shape.of(lambda {}).layout
-
-    assert_equal :other, RubyVM::Shape.of(Struct.new(:x).new(1)).layout
-    assert_equal :other, RubyVM::Shape.of([]).layout
-    assert_equal :other, RubyVM::Shape.of("hello").layout
-    assert_equal :other, RubyVM::Shape.of(/foo/).layout
-    assert_equal :other, RubyVM::Shape.of(2..3).layout
-    assert_equal :other, RubyVM::Shape.of(2**67).layout
-    assert_equal :other, RubyVM::Shape.of(:"aaroniscool#{123}").layout
-  end
-
   def test_str_has_root_shape
     assert_shape_equal(RubyVM::Shape.root_shape, RubyVM::Shape.of(""))
   end
diff --git a/variable.c b/variable.c
index 687fa03631..857d870413 100644
--- a/variable.c
+++ b/variable.c
@@ -1343,7 +1343,7 @@ rb_free_generic_ivar(VALUE obj)
                 }
             }
         }
-        RBASIC_SET_SHAPE_ID(obj, rb_shape_layout(RBASIC_SHAPE_ID(obj)) | ROOT_SHAPE_ID);
+        RBASIC_SET_SHAPE_ID(obj, ROOT_SHAPE_ID);
     }
 }
 
@@ -1395,7 +1395,7 @@ rb_obj_set_fields(VALUE obj, VALUE fields_obj, ID field_name, VALUE original_fie
         }
     }
 
-    RBASIC_SET_SHAPE_ID(obj, rb_shape_layout(RBASIC_SHAPE_ID(obj)) | RBASIC_SHAPE_ID(fields_obj));
+    RBASIC_SET_SHAPE_ID(obj, RBASIC_SHAPE_ID(fields_obj));
 }
 
 void
@@ -1710,7 +1710,6 @@ rb_ivar_delete(VALUE obj, ID id, VALUE undef)
             size_t trailing_fields = new_fields_count - removed_index;
 
             MEMMOVE(&fields[removed_index], &fields[removed_index + 1], VALUE, trailing_fields);
-            RUBY_ASSERT(rb_shape_layout(next_shape_id) == SHAPE_ID_LAYOUT_ROBJECT);
             RBASIC_SET_SHAPE_ID(fields_obj, next_shape_id);
 
             if (FL_TEST_RAW(fields_obj, OBJ_FIELD_HEAP)) {
@@ -1733,7 +1732,7 @@ rb_ivar_delete(VALUE obj, ID id, VALUE undef)
         }
     }
 
-    RBASIC_SET_SHAPE_ID(obj, rb_shape_layout(RBASIC_SHAPE_ID(obj)) | next_shape_id);
+    RBASIC_SET_SHAPE_ID(obj, next_shape_id);
     if (fields_obj != original_fields_obj) {
         switch (type) {
           case T_OBJECT:
@@ -1844,7 +1843,7 @@ imemo_fields_set(VALUE owner, VALUE fields_obj, shape_id_t target_shape_id, ID f
         RUBY_ASSERT(field_name);
         st_insert(table, (st_data_t)field_name, (st_data_t)val);
         RB_OBJ_WRITTEN(fields_obj, Qundef, val);
-        RBASIC_SET_SHAPE_ID(fields_obj, rb_shape_id_with_robject_layout(target_shape_id));
+        RBASIC_SET_SHAPE_ID(fields_obj, target_shape_id);
     }
     else {
         attr_index_t index = RSHAPE_INDEX(target_shape_id);
@@ -1856,7 +1855,7 @@ imemo_fields_set(VALUE owner, VALUE fields_obj, shape_id_t target_shape_id, ID f
         RB_OBJ_WRITE(fields_obj, &table[index], val);
 
         if (index >= RSHAPE_LEN(current_shape_id)) {
-            RBASIC_SET_SHAPE_ID(fields_obj, rb_shape_id_with_robject_layout(target_shape_id));
+            RBASIC_SET_SHAPE_ID(fields_obj, target_shape_id);
         }
     }
 
@@ -2011,12 +2010,11 @@ rb_obj_freeze_inline(VALUE x)
             RB_FL_UNSET_RAW(x, FL_USER2 | FL_USER3); // STR_CHILLED
         }
 
-        // rb_obj_freeze_inline(String)
         shape_id_t shape_id = rb_obj_shape_transition_frozen(x);
         switch (BUILTIN_TYPE(x)) {
           case T_CLASS:
           case T_MODULE:
-            rb_obj_freeze_inline(RCLASS_WRITABLE_ENSURE_FIELDS_OBJ(x));
+            RBASIC_SET_SHAPE_ID(RCLASS_WRITABLE_ENSURE_FIELDS_OBJ(x), shape_id);
             // FIXME: How to do multi-shape?
             RBASIC_SET_SHAPE_ID(x, shape_id);
             break;
@@ -2305,7 +2303,7 @@ rb_copy_generic_ivar(VALUE dest, VALUE obj)
         }
 
         if (!RSHAPE_LEN(dest_shape_id)) {
-            RBASIC_SET_SHAPE_ID(dest, rb_shape_layout(RBASIC_SHAPE_ID(dest)) | dest_shape_id);
+            RBASIC_SET_SHAPE_ID(dest, dest_shape_id);
             return;
         }
 
@@ -4638,7 +4636,6 @@ class_fields_ivar_set(VALUE klass, VALUE fields_obj, ID id, VALUE val, bool conc
         }
 
         if (new_ivar) {
-            RUBY_ASSERT(rb_shape_layout(next_shape_id) == SHAPE_ID_LAYOUT_ROBJECT);
             RBASIC_SET_SHAPE_ID(fields_obj, next_shape_id);
         }
     }
@@ -4661,7 +4658,6 @@ complex:
         RB_OBJ_WRITTEN(fields_obj, Qundef, val);
 
         if (fields_obj != original_fields_obj) {
-            RUBY_ASSERT(rb_shape_layout(next_shape_id) == SHAPE_ID_LAYOUT_ROBJECT);
             RBASIC_SET_SHAPE_ID(fields_obj, next_shape_id);
         }
     }
@@ -4688,7 +4684,7 @@ class_ivar_set(VALUE obj, ID id, VALUE val, bool *new_ivar)
     // TODO: What should we set as the T_CLASS shape_id?
     // In most case we can replicate the single `fields_obj` shape
     // but in namespaced case? Perhaps INVALID_SHAPE_ID?
-    RBASIC_SET_SHAPE_ID(obj, rb_shape_layout(RBASIC_SHAPE_ID(obj)) | RBASIC_SHAPE_ID(new_fields_obj));
+    RBASIC_SET_SHAPE_ID(obj, RBASIC_SHAPE_ID(new_fields_obj));
     return index;
 }
 
@@ -4713,7 +4709,7 @@ rb_fields_tbl_copy(VALUE dst, VALUE src)
     VALUE fields_obj = RCLASS_WRITABLE_FIELDS_OBJ(src);
     if (fields_obj) {
         RCLASS_WRITABLE_SET_FIELDS_OBJ(dst, rb_imemo_fields_clone(fields_obj));
-        RBASIC_SET_SHAPE_ID(dst, rb_shape_layout(RBASIC_SHAPE_ID(dst)) | RBASIC_SHAPE_ID(src));
+        RBASIC_SET_SHAPE_ID(dst, RBASIC_SHAPE_ID(src));
     }
 }
 
diff --git a/vm_insnhelper.c b/vm_insnhelper.c
index f515662bf0..ac0d81092d 100644
--- a/vm_insnhelper.c
+++ b/vm_insnhelper.c
@@ -1412,8 +1412,7 @@ vm_setivar_class(VALUE obj, VALUE val, rb_setivar_cache cache)
     RB_OBJ_WRITE(fields_obj, &rb_imemo_fields_ptr(fields_obj)[cache.index], val);
 
     if (shape_id != dest_shape_id) {
-        // The dest_shape_id comes from the fields_obj
-        RBASIC_SET_SHAPE_ID(obj, SHAPE_ID_LAYOUT_RCLASS | (dest_shape_id & ~SHAPE_ID_LAYOUT_MASK));
+        RBASIC_SET_SHAPE_ID(obj, dest_shape_id);
         RBASIC_SET_SHAPE_ID(fields_obj, dest_shape_id);
     }
 
@@ -1438,9 +1437,7 @@ vm_setivar_default(VALUE obj, ID id, VALUE val, rb_setivar_cache cache)
 
     if (shape_id != dest_shape_id) {
         RBASIC_SET_SHAPE_ID(obj, dest_shape_id);
-        // The dest_shape_id comes from the owner, but fields_obj must always
-        // have layout RObject, so give the fields_object the right layout.
-        RBASIC_SET_SHAPE_ID(fields_obj, rb_shape_id_with_robject_layout(dest_shape_id));
+        RBASIC_SET_SHAPE_ID(fields_obj, dest_shape_id);
     }
 
     RB_DEBUG_COUNTER_INC(ivar_set_ic_hit);
diff --git a/zjit/src/cruby_bindings.inc.rs b/zjit/src/cruby_bindings.inc.rs
index 08c502b0d8..bd832acc96 100644
--- a/zjit/src/cruby_bindings.inc.rs
+++ b/zjit/src/cruby_bindings.inc.rs
@@ -1491,13 +1491,8 @@ pub const SHAPE_ID_HEAP_INDEX_MASK: shape_id_fl_type = 7864320;
 pub const SHAPE_ID_FL_COMPLEX: shape_id_fl_type = 8388608;
 pub const SHAPE_ID_FL_FROZEN: shape_id_fl_type = 16777216;
 pub const SHAPE_ID_FL_HAS_OBJECT_ID: shape_id_fl_type = 33554432;
-pub const SHAPE_ID_LAYOUT_ROBJECT: shape_id_fl_type = 0;
-pub const SHAPE_ID_LAYOUT_RCLASS: shape_id_fl_type = 67108864;
-pub const SHAPE_ID_LAYOUT_RDATA: shape_id_fl_type = 134217728;
-pub const SHAPE_ID_LAYOUT_OTHER: shape_id_fl_type = 201326592;
-pub const SHAPE_ID_LAYOUT_MASK: shape_id_fl_type = 201326592;
 pub const SHAPE_ID_FL_NON_CANONICAL_MASK: shape_id_fl_type = 50331648;
-pub const SHAPE_ID_FLAGS_MASK: shape_id_fl_type = 267911168;
+pub const SHAPE_ID_FLAGS_MASK: shape_id_fl_type = 66584576;
 pub type shape_id_fl_type = u32;
 pub const CONST_DEPRECATED: rb_const_flag_t = 256;
 pub const CONST_VISIBILITY_MASK: rb_const_flag_t = 255;