From: Jonathan Wakely <jwakely@redhat.com>
Date: Wed, 19 Feb 2025 14:48:04 +0000 (+0000)
Subject: libstdc++: Use new type-generic built-ins in <bit> [PR118855]
X-Git-Tag: basepoints/gcc-16~1905
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=e8ad697a75b0870a833366daf687668a57cabb6e;p=thirdparty%2Fgcc.git

libstdc++: Use new type-generic built-ins in <bit> [PR118855]

This makes several functions in <bit> faster to compile, with fewer
expressions to parse and fewer instantiations of __numeric_traits
required.

libstdc++-v3/ChangeLog:

	PR libstdc++/118855
	* include/std/bit (__count_lzero, __count_rzero, __popcount):
	Use type-generic built-ins when available.
---

diff --git a/libstdc++-v3/include/std/bit b/libstdc++-v3/include/std/bit
index 483801ee85b..a4817818d19 100644
--- a/libstdc++-v3/include/std/bit
+++ b/libstdc++-v3/include/std/bit
@@ -205,6 +205,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       using __gnu_cxx::__int_traits;
       constexpr auto _Nd = __int_traits<_Tp>::__digits;
 
+#if _GLIBCXX_USE_BUILTIN_TRAIT(__builtin_clzg)
+      return __builtin_clzg(__x, _Nd);
+#else
       if (__x == 0)
         return _Nd;
 
@@ -242,6 +245,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  unsigned long long __low = __x & __max_ull;
 	  return (_Nd - _Nd_ull) + __builtin_clzll(__low);
 	}
+#endif
     }
 
   template<typename _Tp>
@@ -258,6 +262,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       using __gnu_cxx::__int_traits;
       constexpr auto _Nd = __int_traits<_Tp>::__digits;
 
+#if _GLIBCXX_USE_BUILTIN_TRAIT(__builtin_ctzg)
+      return __builtin_ctzg(__x, _Nd);
+#else
       if (__x == 0)
         return _Nd;
 
@@ -283,6 +290,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  unsigned long long __high = __x >> _Nd_ull;
 	  return __builtin_ctzll(__high) + _Nd_ull;
 	}
+#endif
     }
 
   template<typename _Tp>
@@ -296,6 +304,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     constexpr int
     __popcount(_Tp __x) noexcept
     {
+#if _GLIBCXX_USE_BUILTIN_TRAIT(__builtin_popcountg)
+      return __builtin_popcountg(__x);
+#else
       using __gnu_cxx::__int_traits;
       constexpr auto _Nd = __int_traits<_Tp>::__digits;
 
@@ -319,6 +330,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  unsigned long long __high = __x >> _Nd_ull;
 	  return __builtin_popcountll(__low) + __builtin_popcountll(__high);
 	}
+#endif
     }
 
   template<typename _Tp>