libstdc++: Use memset to optimize std::bitset::set() [PR113807]

As pointed out in the PR we already do this for reset().

libstdc++-v3/ChangeLog:

	PR libstdc++/113807
	* include/std/bitset (bitset::set()): Use memset instead of a
	loop over the individual words.

diff --git a/libstdc++-v3/include/std/bitset b/libstdc++-v3/include/std/bitset
index 3243c6497314fd4f7e4b1c7909cb9e82df4a70dc..16c4040f532f7e774f36a897d45b9f0273dedc76 100644 (file)
--- a/libstdc++-v3/include/std/bitset
+++ b/libstdc++-v3/include/std/bitset
@@ -177,8 +177,15 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       _GLIBCXX14_CONSTEXPR void
       _M_do_set() _GLIBCXX_NOEXCEPT
       {
-       for (size_t __i = 0; __i < _Nw; __i++)
-         _M_w[__i] = ~static_cast<_WordT>(0);
+#if __cplusplus >= 201402L
+       if (__builtin_is_constant_evaluated())
+         {
+           for (_WordT& __w : _M_w)
+             __w = ~static_cast<_WordT>(0);;
+           return;
+         }
+#endif
+       __builtin_memset(_M_w, 0xFF, _Nw * sizeof(_WordT));
       }
 
       _GLIBCXX14_CONSTEXPR void