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

Message ID 20240215114633.50124-1-jwakely@redhat.com
State Accepted
Headers
Series [committed] libstdc++: Use memset to optimize std::bitset::set() [PR113807] |

Checks

Context Check Description
snail/gcc-patch-check success Github commit url

Commit Message

Jonathan Wakely Feb. 15, 2024, 11:46 a.m. UTC 
  Tested aarch64-linux and x86_64-linux. Pushed to trunk.

-- >8 --

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.
---
 libstdc++-v3/include/std/bitset | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)
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Patch

diff --git a/libstdc++-v3/include/std/bitset b/libstdc++-v3/include/std/bitset
index 3243c649731..16c4040f532 100644
--- 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