https://gcc.gnu.org/g:73e5d2f87c257c2c12ee72fd4de9bdbb6a8e1aa9
commit r15-5733-g73e5d2f87c257c2c12ee72fd4de9bdbb6a8e1aa9
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Wed Nov 27 12:28:30 2024 +0000
libstdc++: Remove __builtin_expect from consteval assertion
libstdc++-v3/ChangeLog:
* include/bits/c++config (__glibcxx_assert): Remove useless
__builtin_expect from constexpr-only assertion. Improve
comments.
Diff:
---
libstdc++-v3/include/bits/c++config | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)
diff --git a/libstdc++-v3/include/bits/c++config
b/libstdc++-v3/include/bits/c++config
index c74b03013fdb..a5001d0a0b0b 100644
--- a/libstdc++-v3/include/bits/c++config
+++ b/libstdc++-v3/include/bits/c++config
@@ -626,14 +626,17 @@ namespace std
#endif
#if defined(_GLIBCXX_ASSERTIONS)
-// Enable runtime assertion checks, and also check in constant expressions.
+// When _GLIBCXX_ASSERTIONS is defined we enable runtime assertion checks.
+// These checks will also be done during constant evaluation.
# define __glibcxx_assert(cond)
\
do { \
if (__builtin_expect(!bool(cond), false)) \
_GLIBCXX_ASSERT_FAIL(cond); \
} while (false)
#elif _GLIBCXX_HAVE_IS_CONSTANT_EVALUATED
-// Only check assertions during constant evaluation.
+// _GLIBCXX_ASSERTIONS is not defined, so assertions checks are only enabled
+// during constant evaluation. This ensures we diagnose undefined behaviour
+// in constant expressions.
namespace std
{
__attribute__((__always_inline__,__visibility__("default")))
@@ -643,12 +646,12 @@ namespace std
}
# define __glibcxx_assert(cond)
\
do { \
- if (std::__is_constant_evaluated())
\
- if (__builtin_expect(!bool(cond), false))
\
- std::__glibcxx_assert_fail(); \
+ if (std::__is_constant_evaluated() && !bool(cond)) \
+ std::__glibcxx_assert_fail(); \
} while (false)
#else
-// Don't check any assertions.
+// _GLIBCXX_ASSERTIONS is not defined and __is_constant_evaluated() doesn't
+// work so don't check any assertions.
# define __glibcxx_assert(cond)
#endif
