Eliminate redundant work and branching when marking T_OBJECT (#15274)

Author: luke-gruber

gc.c

@@ -3227,19 +3227,21 @@ rb_gc_mark_children(void *objspace, VALUE obj)
       }
 
       case T_OBJECT: {
+        uint32_t len;
         if (rb_shape_obj_too_complex_p(obj)) {
             gc_mark_tbl_no_pin(ROBJECT_FIELDS_HASH(obj));
+            len = ROBJECT_FIELDS_COUNT_COMPLEX(obj);
         }
         else {
             const VALUE * const ptr = ROBJECT_FIELDS(obj);
 
-            uint32_t len = ROBJECT_FIELDS_COUNT(obj);
+            len = ROBJECT_FIELDS_COUNT_NOT_COMPLEX(obj);
             for (uint32_t i = 0; i < len; i++) {
                 gc_mark_internal(ptr[i]);
             }
         }
 
-        attr_index_t fields_count = ROBJECT_FIELDS_COUNT(obj);
+        attr_index_t fields_count = (attr_index_t)len;
         if (fields_count) {
             VALUE klass = RBASIC_CLASS(obj);
 

ractor.c

@@ -1796,7 +1796,7 @@ obj_traverse_replace_i(VALUE obj, struct obj_traverse_replace_data *data)
                 if (d.stop) return 1;
             }
             else {
-                uint32_t len = ROBJECT_FIELDS_COUNT(obj);
+                uint32_t len = ROBJECT_FIELDS_COUNT_NOT_COMPLEX(obj);
                 VALUE *ptr = ROBJECT_FIELDS(obj);
 
                 for (uint32_t i = 0; i < len; i++) {

shape.h

@@ -367,16 +367,28 @@ ROBJECT_SET_FIELDS_HASH(VALUE obj, const st_table *tbl)
     ROBJECT(obj)->as.heap.fields = (VALUE *)tbl;
 }
 
+static inline uint32_t
+ROBJECT_FIELDS_COUNT_COMPLEX(VALUE obj)
+{
+    return (uint32_t)rb_st_table_size(ROBJECT_FIELDS_HASH(obj));
+}
+
+static inline uint32_t
+ROBJECT_FIELDS_COUNT_NOT_COMPLEX(VALUE obj)
+{
+    RBIMPL_ASSERT_TYPE(obj, RUBY_T_OBJECT);
+    RUBY_ASSERT(!rb_shape_obj_too_complex_p(obj));
+    return RSHAPE(RBASIC_SHAPE_ID(obj))->next_field_index;
+}
+
 static inline uint32_t
 ROBJECT_FIELDS_COUNT(VALUE obj)
 {
     if (rb_shape_obj_too_complex_p(obj)) {
-        return (uint32_t)rb_st_table_size(ROBJECT_FIELDS_HASH(obj));
+        return ROBJECT_FIELDS_COUNT_COMPLEX(obj);
     }
     else {
-        RBIMPL_ASSERT_TYPE(obj, RUBY_T_OBJECT);
-        RUBY_ASSERT(!rb_shape_obj_too_complex_p(obj));
-        return RSHAPE(RBASIC_SHAPE_ID(obj))->next_field_index;
+        return ROBJECT_FIELDS_COUNT_NOT_COMPLEX(obj);
     }
 }