[gcc r16-657] libstdc++: Micro-optimization in std::arg overload for scalars

[Jonathan Wakely]

https://gcc.gnu.org/g:270d23c5b201c8e000f60e05d17577498f409441

commit r16-657-g270d23c5b201c8e000f60e05d17577498f409441
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon May 12 12:56:17 2025 +0100

    libstdc++: Micro-optimization in std::arg overload for scalars
    
    Use __builtin_signbit directly instead of std::signbit.
    
    libstdc++-v3/ChangeLog:
    
            * include/std/complex (arg(T)): Use __builtin_signbit instead of
            std::signbit.
    
    Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>

Diff:
---
 libstdc++-v3/include/std/complex | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/include/std/complex b/libstdc++-v3/include/std/complex
index 67f37d4ec2b7..d9d2d8afda89 100644
--- a/libstdc++-v3/include/std/complex
+++ b/libstdc++-v3/include/std/complex
@@ -2532,8 +2532,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     {
       typedef typename __gnu_cxx::__promote<_Tp>::__type __type;
 #if (_GLIBCXX11_USE_C99_MATH && !_GLIBCXX_USE_C99_FP_MACROS_DYNAMIC)
-      return std::signbit(__x) ? __type(3.1415926535897932384626433832795029L)
-	                       : __type();
+      return __builtin_signbit(__type(__x))
+	       ? __type(3.1415926535897932384626433832795029L) : __type();
 #else
       return std::arg(std::complex<__type>(__x));
 #endif