Tested x86_64-linux. Pushed to trunk.
-- >8 --
The changes in r14-6198-g5e8a30d8b8f4d7 were broken, as I used
_GLIBCXX17_CONSTEXPR for the 'if _GLIBCXX17_CONSTEXPR (true)' condition,
forgetting that it would also be used for the is_constant_evaluated()
check. Using 'if constexpr (std::is_constant_evaluated())' is a bug.
Additionally, relying on __glibcxx_assert_fail to give a "not a constant
expression" error is a problem because at -O0 an undefined reference to
__glibcxx_assert_fail is present in the compiled code. This means you
can't use libstdc++ headers without also linking to libstdc++ for the
symbol definition.
This fix rewrites the __glibcxx_assert macro again. This still avoids
doing the duplicate checks, once for constexpr and once at runtime (if
_GLIBCXX_ASSERTIONS is defined). When _GLIBCXX_ASSERTIONS is defined we
still rely on __glibcxx_assert_fail to give a "not a constant
expression" error during constant evaluation (because when assertions
are defined it's not a problem to emit a reference to the symbol). But
when that macro is not defined, we use a new inline (but not constexpr)
overload of __glibcxx_assert_fail to cause compilation to fail. That
inline function doesn't cause an undefined reference to a symbol in the
library (and will be optimized away anyway).
We can also add always_inline to the __is_constant_evaluated function,
although this doesn't actually matter for -O0 and it's always inlined
with any optimization enabled.
libstdc++-v3/ChangeLog:
PR libstdc++/112882
* include/bits/c++config (__is_constant_evaluated): Add
always_inline attribute.
(_GLIBCXX_DO_ASSERT): Remove macro.
(__glibcxx_assert): Define separately for assertions-enabled and
constexpr-only cases.
---
libstdc++-v3/include/bits/c++config | 33 ++++++++++++++++++++---------
1 file changed, 23 insertions(+), 10 deletions(-)
diff --git a/libstdc++-v3/include/bits/c++config
b/libstdc++-v3/include/bits/c++config
index 284d24d933f..25d37428fc1 100644
--- a/libstdc++-v3/include/bits/c++config
+++ b/libstdc++-v3/include/bits/c++config
@@ -538,6 +538,7 @@ namespace std
// This can be used without checking if the compiler supports the feature.
// The macro _GLIBCXX_HAVE_IS_CONSTANT_EVALUATED can be used to check if
// the compiler support is present to make this function work as expected.
+ __attribute__((__always_inline__))
_GLIBCXX_CONSTEXPR inline bool
__is_constant_evaluated() _GLIBCXX_NOEXCEPT
{
@@ -598,19 +599,31 @@ namespace std
#endif
#if defined(_GLIBCXX_ASSERTIONS)
-# define _GLIBCXX_DO_ASSERT true
-#elif _GLIBCXX_HAVE_IS_CONSTANT_EVALUATED
-# define _GLIBCXX_DO_ASSERT std::__is_constant_evaluated()
-#else
-# define _GLIBCXX_DO_ASSERT false
-#endif
-
+// Enable runtime assertion checks, and also check in constant expressions.
# define __glibcxx_assert(cond)
\
do { \
- if _GLIBCXX17_CONSTEXPR (_GLIBCXX_DO_ASSERT) \
- if (__builtin_expect(!bool(cond), false))
\
- _GLIBCXX_ASSERT_FAIL(cond); \
+ if (__builtin_expect(!bool(cond), false)) \
+ _GLIBCXX_ASSERT_FAIL(cond); \
} while (false)
+#elif _GLIBCXX_HAVE_IS_CONSTANT_EVALUATED
+// Only check assertions during constant evaluation.
+namespace std
+{
+ __attribute__((__always_inline__,__visibility__("default")))
+ inline void
+ __glibcxx_assert_fail()
+ { }
+}
+# define __glibcxx_assert(cond)
\
+ do { \
+ if (std::__is_constant_evaluated())
\
+ if (__builtin_expect(!bool(cond), false))
\
+ std::__glibcxx_assert_fail(); \
+ } while (false)
+#else
+// Don't check any assertions.
+# define __glibcxx_assert(cond)
+#endif
// Macro indicating that TSAN is in use.
#if __SANITIZE_THREAD__
--
2.43.0
