[PATCH v2 2/2] libstdc++: Use new type-generic built-ins in [PR118855]

[Jonathan Wakely]

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.
---

The v1 patch used __has_builtin directly, but this version uses
_GLIBCXX_USE_BUILTIN_TRAIT instead.

Tested x86_64-linux. Pushed to trunk.

 libstdc++-v3/include/std/bit | 12 ++++++++++++
 1 file changed, 12 insertions(+)

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>
-- 
2.48.1