https://git.ruby-lang.org/ruby.git/commit/?id=573eef7c89

From 573eef7c897ff938539270e605445da13093d664 Mon Sep 17 00:00:00 2001
From: Nobuyoshi Nakada <nobu@r...>
Date: Thu, 12 Aug 2021 10:30:42 +0900
Subject: Indicate the slow path of `Check_Type` never return [Bug #18062]

Though this call to `rb_check_type` is just to raise an exception
and never return actually, it can return at least formally.  That
means a caller function looks like it will access `flags` even in
the special-const cases, and some optimizers may unify the access
with the same access just following the call, and re-order it
before the guard.
---
 include/ruby/internal/value_type.h | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/ruby/internal/value_type.h b/include/ruby/internal/value_type.h
index 52b284c..1b4c651 100644
--- a/include/ruby/internal/value_type.h
+++ b/include/ruby/internal/value_type.h
@@ -30,6 +30,7 @@ https://github.com/ruby/ruby/blob/trunk/include/ruby/internal/value_type.h#L30
 #include "ruby/internal/constant_p.h"
 #include "ruby/internal/core/rbasic.h"
 #include "ruby/internal/dllexport.h"
+#include "ruby/internal/error.h"
 #include "ruby/internal/has/builtin.h"
 #include "ruby/internal/special_consts.h"
 #include "ruby/internal/stdbool.h"
@@ -156,6 +157,11 @@ RB_BUILTIN_TYPE(VALUE obj) https://github.com/ruby/ruby/blob/trunk/include/ruby/internal/value_type.h#L157
 {
     RBIMPL_ASSERT_OR_ASSUME(! RB_SPECIAL_CONST_P(obj));
 
+#if 0 && defined __GNUC__ && !defined __clang__
+    /* Don't move the access to `flags` before the preceding
+     * RB_SPECIAL_CONST_P check. */
+    __asm volatile("": : :"memory");
+#endif
     VALUE ret = RBASIC(obj)->flags & RUBY_T_MASK;
     return RBIMPL_CAST((enum ruby_value_type)ret);
 }
@@ -350,7 +356,7 @@ Check_Type(VALUE v, enum ruby_value_type t) https://github.com/ruby/ruby/blob/trunk/include/ruby/internal/value_type.h#L356
     return;
 
   slowpath: /* <- :TODO: mark this label as cold. */
-    rb_check_type(v, t);
+    rb_unexpected_type(v, t);
 }
 
 #endif /* RBIMPL_VALUE_TYPE_H */
-- 
cgit v1.1


--
ML: ruby-changes@q...
Info: http://www.atdot.net/~ko1/quickml/