libstdc++: Redefine __glibcxx_assert to work in C++23 constexpr

The changes in r14-5979 to support unknown references in constant
expressions caused some test regressions. The way that __glibcxx_assert
is defined for constant evaluation no longer works when
_GLIBCXX_ASSERTIONS is defined.

This change simplifies __glibcxx_assert so that there is only one check,
rather than a constexpr one and a conditionally-enabled runtime one. The
constexpr one does not need to use __builtin_unreachable to cause a
compilation failure, because __glibcxx_assert_fail is not usable in
constant expressions, so that will cause a failure too.

As well as fixing the regressions, this makes the code for the
assertions shorter and simpler, so should be quicker to compile, and
might inline better too.

libstdc++-v3/ChangeLog:

	* include/bits/c++config (__glibcxx_assert_fail): Declare even
	when assertions are not enabled.
	(__glibcxx_constexpr_assert): Remove macro.
	(__glibcxx_assert_impl): Remove macro.
	(_GLIBCXX_ASSERT_FAIL): New macro.
	(_GLIBCXX_DO_ASSERT): New macro.
	(__glibcxx_assert): Simplify to a single definition that works
	at runtime and during constant evaluation.
	* testsuite/21_strings/basic_string_view/element_access/char/back_constexpr_neg.cc:
	Adjust expected errors.
	* testsuite/21_strings/basic_string_view/element_access/char/constexpr_neg.cc:
	Likewise.
	* testsuite/21_strings/basic_string_view/element_access/char/front_constexpr_neg.cc:
	Likewise.
	* testsuite/21_strings/basic_string_view/element_access/wchar_t/back_constexpr_neg.cc:
	Likewise.
	* testsuite/21_strings/basic_string_view/element_access/wchar_t/constexpr_neg.cc:
	Likewise.
	* testsuite/21_strings/basic_string_view/element_access/wchar_t/front_constexpr_neg.cc:
	Likewise.
	* testsuite/21_strings/basic_string_view/modifiers/remove_prefix/debug.cc:
	Likewise.
	* testsuite/21_strings/basic_string_view/modifiers/remove_suffix/debug.cc:
	Likewise.
	* testsuite/23_containers/span/back_neg.cc: Likewise.
	* testsuite/23_containers/span/front_neg.cc: Likewise.
	* testsuite/23_containers/span/index_op_neg.cc: Likewise.
	* testsuite/26_numerics/lcm/105844.cc: Likewise.

13 files changed, 36 insertions, 47 deletions

diff --git a/libstdc++-v3/include/bits/c++config b/libstdc++-v3/include/bits/c++config
index 410c136..284d24d 100644
--- a/libstdc++-v3/include/bits/c++config
+++ b/libstdc++-v3/include/bits/c++config
@@ -577,46 +577,41 @@ namespace std
 #undef _GLIBCXX_VERBOSE_ASSERT
 
 // Assert.
-#if defined(_GLIBCXX_ASSERTIONS) \
-  || defined(_GLIBCXX_PARALLEL) || defined(_GLIBCXX_PARALLEL_ASSERTIONS)
-# ifdef _GLIBCXX_VERBOSE_ASSERT
+#ifdef _GLIBCXX_VERBOSE_ASSERT
 namespace std
 {
 #pragma GCC visibility push(default)
-  // Avoid the use of assert, because we're trying to keep the <cassert>
-  // include out of the mix.
+  // Don't use <cassert> because this should be unaffected by NDEBUG.
   extern "C++" _GLIBCXX_NORETURN
   void
-  __glibcxx_assert_fail(const char* __file, int __line,
-			const char* __function, const char* __condition)
+  __glibcxx_assert_fail /* Called when a precondition violation is detected. */
+    (const char* __file, int __line, const char* __function,
+     const char* __condition)
   _GLIBCXX_NOEXCEPT;
 #pragma GCC visibility pop
 }
-#define __glibcxx_assert_impl(_Condition)				\
-  if (__builtin_expect(!bool(_Condition), false))			\
-  {									\
-    __glibcxx_constexpr_assert(false);					\
-    std::__glibcxx_assert_fail(__FILE__, __LINE__, __PRETTY_FUNCTION__,	\
-			       #_Condition);				\
-  }
-# else // ! VERBOSE_ASSERT
-# define __glibcxx_assert_impl(_Condition)		\
-  if (__builtin_expect(!bool(_Condition), false))	\
-  {							\
-    __glibcxx_constexpr_assert(false);			\
-    __builtin_abort();					\
-  }
-# endif
+# define _GLIBCXX_ASSERT_FAIL(_Condition)				\
+  std::__glibcxx_assert_fail(__FILE__, __LINE__, __PRETTY_FUNCTION__,	\
+			     #_Condition)
+#else // ! VERBOSE_ASSERT
+# define _GLIBCXX_ASSERT_FAIL(_Condition) __builtin_abort()
 #endif
 
 #if defined(_GLIBCXX_ASSERTIONS)
-# define __glibcxx_assert(cond) \
-  do { __glibcxx_assert_impl(cond); } while (false)
+# define _GLIBCXX_DO_ASSERT true
+#elif _GLIBCXX_HAVE_IS_CONSTANT_EVALUATED
+# define _GLIBCXX_DO_ASSERT std::__is_constant_evaluated()
 #else
-# define __glibcxx_assert(cond) \
-  do { __glibcxx_constexpr_assert(cond); } while (false)
+# define _GLIBCXX_DO_ASSERT false
 #endif
 
+# define __glibcxx_assert(cond)						\
+  do {									\
+    if _GLIBCXX17_CONSTEXPR (_GLIBCXX_DO_ASSERT)			\
+      if (__builtin_expect(!bool(cond), false))				\
+	_GLIBCXX_ASSERT_FAIL(cond);					\
+  } while (false)
+
 // Macro indicating that TSAN is in use.
 #if __SANITIZE_THREAD__
 #  define _GLIBCXX_TSAN 1
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string_view/element_access/char/back_constexpr_neg.cc b/libstdc++-v3/testsuite/21_strings/basic_string_view/element_access/char/back_constexpr_neg.cc
index ffbc306..39410dd 100644
--- a/libstdc++-v3/testsuite/21_strings/basic_string_view/element_access/char/back_constexpr_neg.cc
+++ b/libstdc++-v3/testsuite/21_strings/basic_string_view/element_access/char/back_constexpr_neg.cc
@@ -31,5 +31,4 @@ back()
 
 static_assert(back() != 'a'); // { dg-error "non-constant condition" }
 
-// { dg-prune-output "in 'constexpr' expansion" }
-// { dg-prune-output "unreachable" }
+// { dg-error "assert_fail" "" { target *-*-* } 0 }
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string_view/element_access/char/constexpr_neg.cc b/libstdc++-v3/testsuite/21_strings/basic_string_view/element_access/char/constexpr_neg.cc
index 3e718bf..59c465b 100644
--- a/libstdc++-v3/testsuite/21_strings/basic_string_view/element_access/char/constexpr_neg.cc
+++ b/libstdc++-v3/testsuite/21_strings/basic_string_view/element_access/char/constexpr_neg.cc
@@ -30,5 +30,4 @@ test()
 
 static_assert(test() == 0); // { dg-error "non-constant condition" }
 
-// { dg-prune-output "in 'constexpr' expansion" }
-// { dg-prune-output "unreachable" }
+// { dg-error "assert_fail" "" { target *-*-* } 0 }
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string_view/element_access/char/front_constexpr_neg.cc b/libstdc++-v3/testsuite/21_strings/basic_string_view/element_access/char/front_constexpr_neg.cc
index f46fe40..257b043 100644
--- a/libstdc++-v3/testsuite/21_strings/basic_string_view/element_access/char/front_constexpr_neg.cc
+++ b/libstdc++-v3/testsuite/21_strings/basic_string_view/element_access/char/front_constexpr_neg.cc
@@ -31,5 +31,4 @@ front()
 
 static_assert(front() != 'a'); // { dg-error "non-constant condition" }
 
-// { dg-prune-output "in 'constexpr' expansion" }
-// { dg-prune-output "unreachable" }
+// { dg-error "assert_fail" "" { target *-*-* } 0 }
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string_view/element_access/wchar_t/back_constexpr_neg.cc b/libstdc++-v3/testsuite/21_strings/basic_string_view/element_access/wchar_t/back_constexpr_neg.cc
index c40b2f1..3ad9cea 100644
--- a/libstdc++-v3/testsuite/21_strings/basic_string_view/element_access/wchar_t/back_constexpr_neg.cc
+++ b/libstdc++-v3/testsuite/21_strings/basic_string_view/element_access/wchar_t/back_constexpr_neg.cc
@@ -31,5 +31,4 @@ back()
 
 static_assert(back() != L'a'); // { dg-error "non-constant condition" }
 
-// { dg-prune-output "in 'constexpr' expansion" }
-// { dg-prune-output "unreachable" }
+// { dg-error "assert_fail" "" { target *-*-* } 0 }
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string_view/element_access/wchar_t/constexpr_neg.cc b/libstdc++-v3/testsuite/21_strings/basic_string_view/element_access/wchar_t/constexpr_neg.cc
index 46c56e7..ec676d7 100644
--- a/libstdc++-v3/testsuite/21_strings/basic_string_view/element_access/wchar_t/constexpr_neg.cc
+++ b/libstdc++-v3/testsuite/21_strings/basic_string_view/element_access/wchar_t/constexpr_neg.cc
@@ -30,5 +30,4 @@ test()
 
 static_assert(test() == 0); // { dg-error "non-constant condition" }
 
-// { dg-prune-output "in 'constexpr' expansion" }
-// { dg-prune-output "unreachable" }
+// { dg-error "assert_fail" "" { target *-*-* } 0 }
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string_view/element_access/wchar_t/front_constexpr_neg.cc b/libstdc++-v3/testsuite/21_strings/basic_string_view/element_access/wchar_t/front_constexpr_neg.cc
index 89367e8..c3ee7ff 100644
--- a/libstdc++-v3/testsuite/21_strings/basic_string_view/element_access/wchar_t/front_constexpr_neg.cc
+++ b/libstdc++-v3/testsuite/21_strings/basic_string_view/element_access/wchar_t/front_constexpr_neg.cc
@@ -31,5 +31,4 @@ front()
 
 static_assert(front() != L'a'); // { dg-error "non-constant condition" }
 
-// { dg-prune-output "in 'constexpr' expansion" }
-// { dg-prune-output "unreachable" }
+// { dg-error "assert_fail" "" { target *-*-* } 0 }
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string_view/modifiers/remove_prefix/debug.cc b/libstdc++-v3/testsuite/21_strings/basic_string_view/modifiers/remove_prefix/debug.cc
index 3720458..87a9660 100644
--- a/libstdc++-v3/testsuite/21_strings/basic_string_view/modifiers/remove_prefix/debug.cc
+++ b/libstdc++-v3/testsuite/21_strings/basic_string_view/modifiers/remove_prefix/debug.cc
@@ -7,7 +7,7 @@ check_remove_prefix()
 {
   std::string_view sv("123");
   sv.remove_prefix(4);
-  // { dg-error "not a constant expression" "" { target *-*-* } 0 }
+  // { dg-error "assert_fail" "" { target *-*-* } 0 }
   return true;
 }
 
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string_view/modifiers/remove_suffix/debug.cc b/libstdc++-v3/testsuite/21_strings/basic_string_view/modifiers/remove_suffix/debug.cc
index a549e4c..513aa8c 100644
--- a/libstdc++-v3/testsuite/21_strings/basic_string_view/modifiers/remove_suffix/debug.cc
+++ b/libstdc++-v3/testsuite/21_strings/basic_string_view/modifiers/remove_suffix/debug.cc
@@ -7,7 +7,7 @@ check_remove_suffix()
 {
   std::string_view sv("123");
   sv.remove_suffix(4);
-  // { dg-error "not a constant expression" "" { target *-*-* } 0 }
+  // { dg-error "assert_fail" "" { target *-*-* } 0 }
   return true;
 }
 
diff --git a/libstdc++-v3/testsuite/23_containers/span/back_neg.cc b/libstdc++-v3/testsuite/23_containers/span/back_neg.cc
index dce512a..494964b 100644
--- a/libstdc++-v3/testsuite/23_containers/span/back_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/span/back_neg.cc
@@ -30,5 +30,5 @@ test01(bool b)
 
 static_assert(test01(false));
 static_assert(test01(true)); // { dg-error "non-constant" }
-// { dg-error "unreachable" "" { target *-*-* } 0 }
-// { dg-prune-output "in 'constexpr' expansion" }
+// { dg-error "assert_fail" "" { target *-*-* } 0 }
+// { dg-prune-output "called in a constant expression" }
diff --git a/libstdc++-v3/testsuite/23_containers/span/front_neg.cc b/libstdc++-v3/testsuite/23_containers/span/front_neg.cc
index b2c5e9c..29fe3f0 100644
--- a/libstdc++-v3/testsuite/23_containers/span/front_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/span/front_neg.cc
@@ -30,5 +30,5 @@ test01(bool b)
 
 static_assert(test01(false));
 static_assert(test01(true)); // { dg-error "non-constant" }
-// { dg-error "unreachable" "" { target *-*-* } 0 }
-// { dg-prune-output "in 'constexpr' expansion" }
+// { dg-error "assert_fail" "" { target *-*-* } 0 }
+// { dg-prune-output "called in a constant expression" }
diff --git a/libstdc++-v3/testsuite/23_containers/span/index_op_neg.cc b/libstdc++-v3/testsuite/23_containers/span/index_op_neg.cc
index a2cdb8a4..8a3e3e9 100644
--- a/libstdc++-v3/testsuite/23_containers/span/index_op_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/span/index_op_neg.cc
@@ -30,5 +30,5 @@ test01(bool b)
 
 static_assert(test01(false));
 static_assert(test01(true)); // { dg-error "non-constant" }
-// { dg-error "unreachable" "" { target *-*-* } 0 }
-// { dg-prune-output "in 'constexpr' expansion" }
+// { dg-error "assert_fail" "" { target *-*-* } 0 }
+// { dg-prune-output "called in a constant expression" }
diff --git a/libstdc++-v3/testsuite/26_numerics/lcm/105844.cc b/libstdc++-v3/testsuite/26_numerics/lcm/105844.cc
index d853974..65a999c 100644
--- a/libstdc++-v3/testsuite/26_numerics/lcm/105844.cc
+++ b/libstdc++-v3/testsuite/26_numerics/lcm/105844.cc
@@ -21,4 +21,4 @@ constexpr int e = std::lcm(500000u, 499999); // { dg-error "in .constexpr." }
 constexpr int f = std::lcm(499999u, 500000); // { dg-error "in .constexpr." }
 
 // { dg-error "overflow" "" { target *-*-* } 0 }
-// { dg-error "unreachable" "" { target *-*-* } 0 }
+// { dg-error "assert_fail" "" { target *-*-* } 0 }