From: Jonathan Wakely <jwakely@redhat.com>
Date: Fri, 23 Sep 2022 12:39:31 +0000 (+0100)
Subject: libstdc++: Micro-optimizaion for std::bitset stream extraction
X-Git-Tag: basepoints/gcc-14~4389
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ab98b4c0725eb7c0f03d319ef3e22ae761b2698a;p=thirdparty%2Fgcc.git

libstdc++: Micro-optimizaion for std::bitset stream extraction

Don't bother trying to copy any characters for bitset<0>.

libstdc++-v3/ChangeLog:

	* include/std/bitset (operator>>): Do not copy for N==0.
	* testsuite/20_util/bitset/io/input.cc: Add comment.
---

diff --git a/libstdc++-v3/include/std/bitset b/libstdc++-v3/include/std/bitset
index 83c6416b7706..6dbc58c6429e 100644
--- a/libstdc++-v3/include/std/bitset
+++ b/libstdc++-v3/include/std/bitset
@@ -1615,7 +1615,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 
       if (__tmp.empty() && _Nb)
 	__state |= __ios_base::failbit;
-      else
+      else if _GLIBCXX17_CONSTEXPR (_Nb)
 	__x._M_copy_from_string(__tmp, static_cast<size_t>(0), _Nb,
 				__zero, __one);
       if (__state)
diff --git a/libstdc++-v3/testsuite/20_util/bitset/io/input.cc b/libstdc++-v3/testsuite/20_util/bitset/io/input.cc
index 939861b171ea..0f22cefbb5b7 100644
--- a/libstdc++-v3/testsuite/20_util/bitset/io/input.cc
+++ b/libstdc++-v3/testsuite/20_util/bitset/io/input.cc
@@ -39,7 +39,7 @@ void test01()
   ss.clear();
   ss.str("*");
   ss >> b0;
-  VERIFY( ss.rdstate() == ios_base::goodbit );
+  VERIFY( ss.rdstate() == ios_base::goodbit ); // LWG 3199
 }
 
 int main()