libstdc++: Simplify constexpr checks in std::char_traits [PR 91488]

This removes the 'static' keyword from the helper functions added by
r8-1294 to detect whether the char_traits member functions can be
evaluated at compile time. This prevents the "inlining failed" error
reported in the PR.

The new testcase from the PR is added to the libitm testsuite, because
that's where we can be sure it's OK to use the -fgnu-tm option.

As a drive-by fix, the feature test macros for C++20 P0980R1 support are
made to depend on whether __cpp_lib_is_constant_evaluated is defined.

Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
	PR libstdc++/91488

libstdc++-v3/ChangeLog:

	* include/bits/basic_string.h (__cpp_lib_constexpr_string): Only
	define C++20 value when std::is_constant_evaluated is available.
	* include/bits/char_traits.h (__cpp_lib_constexpr_char_traits):
	Likewise.
	(__constant_string_p, __constant_array_p): Give external
	linkage.
	* include/std/version (__cpp_lib_constexpr_char_traits)
	(__cpp_lib_constexpr_string): Only define C++20 values when
	is_constant_evaluated is available.

libitm/ChangeLog:

	* testsuite/libitm.c++/libstdc++-pr91488.C: New test.

(cherry picked from commit b376b1ef38971b84975ad1540bf5d2ae0b924e76)

diff --git a/libitm/testsuite/libitm.c++/libstdc++-pr91488.C b/libitm/testsuite/libitm.c++/libstdc++-pr91488.C
new file mode 100644 (file)
index 0000000..e9e82bd
--- /dev/null
+++ b/libitm/testsuite/libitm.c++/libstdc++-pr91488.C
@@ -0,0 +1,9 @@
+// PR libstdc++/91488 "inlining failed in call to always_inline"
+// { dg-do run }
+// { dg-additional-options "-O1" }
+
+#include <string>
+
+int main() {
+    return std::char_traits<char>::length("");
+}

diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h
index 84356adc7ae5ffe167d0fb52052a5dfcfe9e7e87..037040740ab49afd4d5aa3ed579e1bee65565c38 100644 (file)
--- a/libstdc++-v3/include/bits/basic_string.h
+++ b/libstdc++-v3/include/bits/basic_string.h
@@ -52,12 +52,13 @@ namespace std _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
-#if __cplusplus == 201703L
+#ifdef __cpp_lib_is_constant_evaluated
+// Support P1032R1 in C++20 (but not P0980R1 yet).
+# define __cpp_lib_constexpr_string 201811L
+#elif __cplusplus >= 201703L
 // Support P0426R1 changes to char_traits in C++17.
 # define __cpp_lib_constexpr_string 201611L
 #elif __cplusplus > 201703L
-// Also support P1032R1 in C++20 (but not P0980R1 yet).
-# define __cpp_lib_constexpr_string 201811L
 #endif
 
 #if _GLIBCXX_USE_CXX11_ABI

diff --git a/libstdc++-v3/include/bits/char_traits.h b/libstdc++-v3/include/bits/char_traits.h
index 95fb7c1ee8962f873ee5ac20e7049d200a055ed0..c143d74a9ba9eb60ebc5d3353d678af3bfc80b49 100644 (file)
--- a/libstdc++-v3/include/bits/char_traits.h
+++ b/libstdc++-v3/include/bits/char_traits.h
@@ -237,12 +237,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
 #if __cplusplus >= 201703L
 
-#if __cplusplus == 201703L
-// Unofficial macro indicating P0426R1 support
-# define __cpp_lib_constexpr_char_traits 201611L
-#else
-// Also support P1032R1 in C++20
+#ifdef __cpp_lib_is_constant_evaluated
+// Unofficial macro indicating P1032R1 support in C++20
 # define __cpp_lib_constexpr_char_traits 201811L
+#else
+// Unofficial macro indicating P0426R1 support in C++17
+# define __cpp_lib_constexpr_char_traits 201611L
 #endif
 
   /**
@@ -253,7 +253,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  Assumes that _CharT is a built-in character type.
    */
   template<typename _CharT>
-    static _GLIBCXX_ALWAYS_INLINE constexpr bool
+    _GLIBCXX_ALWAYS_INLINE constexpr bool
     __constant_string_p(const _CharT* __s)
     {
 #ifdef _GLIBCXX_HAVE_BUILTIN_IS_CONSTANT_EVALUATED
@@ -276,7 +276,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  Assumes that _CharT is a built-in character type.
    */
   template<typename _CharT>
-    static _GLIBCXX_ALWAYS_INLINE constexpr bool
+    _GLIBCXX_ALWAYS_INLINE constexpr bool
     __constant_char_array_p(const _CharT* __a, size_t __n)
     {
 #ifdef _GLIBCXX_HAVE_BUILTIN_IS_CONSTANT_EVALUATED

diff --git a/libstdc++-v3/include/std/version b/libstdc++-v3/include/std/version
index 8d0b2b95f348bcd180c5409541b7bddcf7430306..5288cc55a0bf73ce36108e5f43a5cc5fa97aa2dd 100644 (file)
--- a/libstdc++-v3/include/std/version
+++ b/libstdc++-v3/include/std/version
@@ -213,14 +213,18 @@
 // FIXME: #define __cpp_lib_execution 201902L
 #define __cpp_lib_integer_comparison_functions 202002L
 #define __cpp_lib_constexpr_algorithms 201806L
-#define __cpp_lib_constexpr_char_traits 201811L
+#ifdef __cpp_lib_is_constant_evaluated
+# define __cpp_lib_constexpr_char_traits 201811L
+#endif
 #define __cpp_lib_constexpr_complex 201711L
 #define __cpp_lib_constexpr_dynamic_alloc 201907L
 #define __cpp_lib_constexpr_functional 201907L
 #define __cpp_lib_constexpr_iterator 201811L
 #define __cpp_lib_constexpr_memory 201811L
 #define __cpp_lib_constexpr_numeric 201911L
-#define __cpp_lib_constexpr_string 201811L
+#ifdef __cpp_lib_is_constant_evaluated
+# define __cpp_lib_constexpr_string 201811L
+#endif
 #define __cpp_lib_constexpr_string_view 201811L
 #define __cpp_lib_constexpr_tuple 201811L
 #define __cpp_lib_constexpr_utility 201811L