Add SHAPE_ID_HAS_IVAR_MASK for quick ivar check

This allow checking if an object has ivars with just a shape_id
mask.

Author: byroot

shape.c

@@ -1234,6 +1234,23 @@ rb_shape_verify_consistency(VALUE obj, shape_id_t shape_id)
         }
     }
 
+    // Make sure SHAPE_ID_HAS_IVAR_MASK is valid.
+    if (rb_shape_too_complex_p(shape_id)) {
+        RUBY_ASSERT(shape_id & SHAPE_ID_HAS_IVAR_MASK);
+    }
+    else {
+        attr_index_t ivar_count = RSHAPE_LEN(shape_id);
+        if (has_object_id) {
+            ivar_count--;
+        }
+        if (ivar_count) {
+            RUBY_ASSERT(shape_id & SHAPE_ID_HAS_IVAR_MASK);
+        }
+        else {
+            RUBY_ASSERT(!(shape_id & SHAPE_ID_HAS_IVAR_MASK));
+        }
+    }
+
     uint8_t flags_heap_index = rb_shape_heap_index(shape_id);
     if (RB_TYPE_P(obj, T_OBJECT)) {
         size_t shape_id_slot_size = rb_shape_tree.capacities[flags_heap_index - 1] * sizeof(VALUE) + sizeof(struct RBasic);
@@ -1524,13 +1541,15 @@ Init_default_shapes(void)
     root->type = SHAPE_ROOT;
     rb_shape_tree.root_shape = root;
     RUBY_ASSERT(raw_shape_id(rb_shape_tree.root_shape) == ROOT_SHAPE_ID);
+    RUBY_ASSERT(!(raw_shape_id(rb_shape_tree.root_shape) & SHAPE_ID_HAS_IVAR_MASK));
 
     bool dontcare;
     rb_shape_t *root_with_obj_id = get_next_shape_internal(root, id_object_id, SHAPE_OBJ_ID, &dontcare, true);
     RUBY_ASSERT(raw_shape_id(root_with_obj_id) == ROOT_SHAPE_WITH_OBJ_ID);
     RUBY_ASSERT(root_with_obj_id->type == SHAPE_OBJ_ID);
     RUBY_ASSERT(root_with_obj_id->edge_name == id_object_id);
     RUBY_ASSERT(root_with_obj_id->next_field_index == 1);
+    RUBY_ASSERT(!(raw_shape_id(root_with_obj_id) & SHAPE_ID_HAS_IVAR_MASK));
 }
 
 void

shape.h

@@ -10,6 +10,14 @@ typedef uint32_t shape_id_t;
 
 STATIC_ASSERT(shape_id_num_bits, SHAPE_ID_NUM_BITS == sizeof(shape_id_t) * CHAR_BIT);
 
+enum shape_flags {
+    SHAPE_FL_FROZEN             = 1 << 0,
+    SHAPE_FL_HAS_OBJECT_ID      = 1 << 1,
+    SHAPE_FL_TOO_COMPLEX        = 1 << 2,
+
+    SHAPE_FL_NON_CANONICAL_MASK = SHAPE_FL_FROZEN | SHAPE_FL_HAS_OBJECT_ID,
+};
+
 #define SHAPE_BUFFER_SIZE (1 << SHAPE_ID_OFFSET_NUM_BITS)
 #define SHAPE_ID_OFFSET_MASK (SHAPE_BUFFER_SIZE - 1)
 #define SHAPE_ID_FLAGS_MASK (shape_id_t)(((1 << (SHAPE_ID_NUM_BITS - SHAPE_ID_OFFSET_NUM_BITS)) - 1) << SHAPE_ID_OFFSET_NUM_BITS)
@@ -23,6 +31,11 @@ STATIC_ASSERT(shape_id_num_bits, SHAPE_ID_NUM_BITS == sizeof(shape_id_t) * CHAR_
 #define SHAPE_ID_HEAP_INDEX_MAX ((1 << SHAPE_ID_HEAP_INDEX_BITS) - 1)
 #define SHAPE_ID_HEAP_INDEX_MASK (SHAPE_ID_HEAP_INDEX_MAX << SHAPE_ID_HEAP_INDEX_OFFSET)
 
+// This masks allows to check if a shape_id contains any ivar.
+// It rely on ROOT_SHAPE_WITH_OBJ_ID==1.
+#define SHAPE_ID_HAS_IVAR_MASK 0x27fffe
+STATIC_ASSERT(shape_id_has_ivar_mask, SHAPE_ID_HAS_IVAR_MASK == (SHAPE_ID_FL_TOO_COMPLEX | (SHAPE_ID_OFFSET_MASK - 1)));
+
 // The interpreter doesn't care about frozen status or slot size when reading ivars.
 // So we normalize shape_id by clearing these bits to improve cache hits.
 // JITs however might care about it.
@@ -72,14 +85,6 @@ enum shape_type {
     SHAPE_OBJ_ID,
 };
 
-enum shape_flags {
-    SHAPE_FL_FROZEN             = 1 << 0,
-    SHAPE_FL_HAS_OBJECT_ID      = 1 << 1,
-    SHAPE_FL_TOO_COMPLEX        = 1 << 2,
-
-    SHAPE_FL_NON_CANONICAL_MASK = SHAPE_FL_FROZEN | SHAPE_FL_HAS_OBJECT_ID,
-};
-
 typedef struct {
     /* object shapes */
     rb_shape_t *shape_list;
@@ -327,6 +332,18 @@ rb_shape_obj_has_id(VALUE obj)
     return rb_shape_has_object_id(RBASIC_SHAPE_ID(obj));
 }
 
+static inline bool
+rb_shape_has_ivars(shape_id_t shape_id)
+{
+    return shape_id & SHAPE_ID_HAS_IVAR_MASK;
+}
+
+static inline bool
+rb_shape_obj_has_ivars(VALUE obj)
+{
+    return rb_shape_has_ivars(RBASIC_SHAPE_ID(obj));
+}
+
 // For ext/objspace
 RUBY_SYMBOL_EXPORT_BEGIN
 typedef void each_shape_callback(shape_id_t shape_id, void *data);

string.c

@@ -388,12 +388,7 @@ fstring_hash(VALUE str)
 static inline bool
 BARE_STRING_P(VALUE str)
 {
-    if (RBASIC_CLASS(str) != rb_cString) return false;
-
-    if (FL_TEST_RAW(str, FL_EXIVAR)) {
-        return rb_ivar_count(str) == 0;
-    }
-    return true;
+    return RBASIC_CLASS(str) == rb_cString && !rb_shape_obj_has_ivars(str);
 }
 
 static inline st_index_t

yjit/bindgen/src/main.rs

@@ -103,6 +103,7 @@ fn main() {
         .allowlist_function("rb_yjit_shape_capacity")
         .allowlist_function("rb_yjit_shape_index")
         .allowlist_var("SHAPE_ID_NUM_BITS")
+        .allowlist_var("SHAPE_ID_HAS_IVAR_MASK")
 
         // From ruby/internal/intern/object.h
         .allowlist_function("rb_obj_is_kind_of")

yjit/src/codegen.rs

@@ -6278,8 +6278,10 @@ fn jit_rb_str_dup(
     // Check !FL_ANY_RAW(str, FL_EXIVAR), which is part of BARE_STRING_P.
     let recv_opnd = asm.stack_pop(1);
     let recv_opnd = asm.load(recv_opnd);
-    let flags_opnd = Opnd::mem(64, recv_opnd, RUBY_OFFSET_RBASIC_FLAGS);
-    asm.test(flags_opnd, Opnd::Imm(RUBY_FL_EXIVAR as i64));
+
+    let shape_id_offset = unsafe { rb_shape_id_offset() };
+    let shape_opnd = Opnd::mem(SHAPE_ID_NUM_BITS as u8, recv_opnd, shape_id_offset);
+    asm.test(shape_opnd, Opnd::Imm(SHAPE_ID_HAS_IVAR_MASK as i64));
     asm.jnz(Target::side_exit(Counter::send_str_dup_exivar));
 
     // Call rb_str_dup