[gcc r13-3577] libstdc++: Small extended float support tweaks

[gcc r13-3577] libstdc++: Small extended float support tweaks

[Jakub Jelinek]

https://gcc.gnu.org/g:cbf56503d5e2bbafb06a507cb37d30805a1013a0

commit r13-3577-gcbf56503d5e2bbafb06a507cb37d30805a1013a0
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Mon Oct 31 16:47:23 2022 +0100

    libstdc++: Small extended float support tweaks
    
    The following patch
    1) enables the std::float128_t overloads for x86 with glibc 2.26+
    2) makes std::nextafter(std::float16_t, std::float16_t) and
       std::nextafter(std::bfloat16_t, std::bfloat16_t) constexpr
    3) adds (small) testsuite coverage for that
    
    2022-10-21  Jakub Jelinek  <jakub@redhat.com>
    
            * config/os/gnu-linux/os_defines.h (_GLIBCXX_HAVE_FLOAT128_MATH):
            Uncomment.
            * include/c_global/cmath (nextafter(_Float16, _Float16)): Make it constexpr.
            If std::__is_constant_evaluated() call __builtin_nextafterf16.
            (nextafter(__gnu_cxx::__bfloat16_t, __gnu_cxx::__bfloat16_t)): Similarly
            but call __builtin_nextafterf16b.
            * testsuite/26_numerics/headers/cmath/nextafter_c++23.cc (test): Add
            static assertions to test constexpr nextafter.

Diff:
---
 libstdc++-v3/config/os/gnu-linux/os_defines.h                     | 2 +-
 libstdc++-v3/include/c_global/cmath                               | 8 ++++++--
 .../testsuite/26_numerics/headers/cmath/nextafter_c++23.cc        | 2 ++
 3 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/libstdc++-v3/config/os/gnu-linux/os_defines.h b/libstdc++-v3/config/os/gnu-linux/os_defines.h
index e5b640a0738..044b4fc91a9 100644
--- a/libstdc++-v3/config/os/gnu-linux/os_defines.h
+++ b/libstdc++-v3/config/os/gnu-linux/os_defines.h
@@ -57,7 +57,7 @@
 	|| (defined(__powerpc__) && defined(_ARCH_PWR8) \
 	    && defined(__LITTLE_ENDIAN__) && (_CALL_ELF == 2) \
 	    && defined(__FLOAT128__)))
-//# define _GLIBCXX_HAVE_FLOAT128_MATH 1
+# define _GLIBCXX_HAVE_FLOAT128_MATH 1
 #endif
 
 #if __GLIBC_PREREQ(2, 27)
diff --git a/libstdc++-v3/include/c_global/cmath b/libstdc++-v3/include/c_global/cmath
index 555d6440849..e52055ac474 100644
--- a/libstdc++-v3/include/c_global/cmath
+++ b/libstdc++-v3/include/c_global/cmath
@@ -2755,9 +2755,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   nearbyint(_Float16 __x)
   { return _Float16(__builtin_nearbyintf(__x)); }
 
-  inline _Float16
+  constexpr _Float16
   nextafter(_Float16 __x, _Float16 __y)
   {
+    if (std::__is_constant_evaluated())
+      return __builtin_nextafterf16(__x, __y);
 #ifdef __INT16_TYPE__
     using __float16_int_type = __INT16_TYPE__;
 #else
@@ -3471,9 +3473,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   nearbyint(__gnu_cxx::__bfloat16_t __x)
   { return __gnu_cxx::__bfloat16_t(__builtin_nearbyintf(__x)); }
 
-  inline __gnu_cxx::__bfloat16_t
+  constexpr __gnu_cxx::__bfloat16_t
   nextafter(__gnu_cxx::__bfloat16_t __x, __gnu_cxx::__bfloat16_t __y)
   {
+    if (std::__is_constant_evaluated())
+      return __builtin_nextafterf16b(__x, __y);
 #ifdef __INT16_TYPE__
     using __bfloat16_int_type = __INT16_TYPE__;
 #else
diff --git a/libstdc++-v3/testsuite/26_numerics/headers/cmath/nextafter_c++23.cc b/libstdc++-v3/testsuite/26_numerics/headers/cmath/nextafter_c++23.cc
index 45aa3b74b25..8d7daa9208d 100644
--- a/libstdc++-v3/testsuite/26_numerics/headers/cmath/nextafter_c++23.cc
+++ b/libstdc++-v3/testsuite/26_numerics/headers/cmath/nextafter_c++23.cc
@@ -100,6 +100,8 @@ test ()
   VERIFY(std::fpclassify(t36) == FP_NAN);
   T t37 = std::nextafter(T(-0.0), T());
   VERIFY(t37 == T() && !std::signbit(t37));
+  static_assert(std::nextafter(T(1.0), T(2.0)) > T(1.0));
+  static_assert(std::nextafter(std::nextafter(T(1.0), T(5.0)), T(0.0)) == T(1.0));
 }
 
 int