From e01e89f55c82be8db5d8ccbf305ee38e3769e582 Mon Sep 17 00:00:00 2001
From: John Hawthorn <john@hawthorn.email>
Date: Thu, 22 May 2025 16:07:22 -0700
Subject: [PATCH] Avoid calling RCLASS_SUPER in rb_class_superclass

---
 benchmark/class_superclass.yml | 23 +++++++++++++++++++++++
 object.c                       | 17 ++++++++---------
 2 files changed, 31 insertions(+), 9 deletions(-)
 create mode 100644 benchmark/class_superclass.yml

diff --git a/benchmark/class_superclass.yml b/benchmark/class_superclass.yml
new file mode 100644
index 0000000000..847ff811f1
--- /dev/null
+++ b/benchmark/class_superclass.yml
@@ -0,0 +1,23 @@
+prelude: |
+  class SimpleClass; end
+  class OneModuleClass
+    1.times { include Module.new }
+  end
+  class MediumClass
+    10.times { include Module.new }
+  end
+  class LargeClass
+    100.times { include Module.new }
+  end
+benchmark:
+  object_class_superclass: |
+    Object.superclass
+  simple_class_superclass: |
+    SimpleClass.superclass
+  one_module_class: |
+    OneModuleClass.superclass
+  medium_class_superclass: |
+    MediumClass.superclass
+  large_class_superclass: |
+    LargeClass.superclass
+loop_count: 20000000
diff --git a/object.c b/object.c
index f5f5759d11..b9b6f928aa 100644
--- a/object.c
+++ b/object.c
@@ -2259,23 +2259,22 @@ rb_class_superclass(VALUE klass)
 {
     RUBY_ASSERT(RB_TYPE_P(klass, T_CLASS));
 
-    VALUE super = RCLASS_SUPER(klass);
-    VALUE *superclasses;
-    size_t superclasses_depth;
+    VALUE *superclasses = RCLASS_SUPERCLASSES(klass);
+    size_t superclasses_depth = RCLASS_SUPERCLASS_DEPTH(klass);
 
-    if (!super) {
-        if (klass == rb_cBasicObject) return Qnil;
+    if (klass == rb_cBasicObject) return Qnil;
+
+    if (!superclasses) {
+        RUBY_ASSERT(!RCLASS_SUPER(klass));
         rb_raise(rb_eTypeError, "uninitialized class");
     }
 
-    superclasses_depth = RCLASS_SUPERCLASS_DEPTH(klass);
     if (!superclasses_depth) {
         return Qnil;
     }
     else {
-        superclasses = RCLASS_SUPERCLASSES(klass);
-        super = superclasses[superclasses_depth - 1];
-        RUBY_ASSERT(RB_TYPE_P(klass, T_CLASS));
+        VALUE super = superclasses[superclasses_depth - 1];
+        RUBY_ASSERT(RB_TYPE_P(super, T_CLASS));
         return super;
     }
 }