From: Jonathan Wakely <jwakely@redhat.com>
Date: Wed, 1 Dec 2021 20:58:58 +0000 (+0000)
Subject: libstdc++: Restore unconditional atomic load in COW std::string
X-Git-Tag: basepoints/gcc-13~2560
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b5a568683f71b4a8b1e4e45a43484398e9a66ff2;p=thirdparty%2Fgcc.git

libstdc++: Restore unconditional atomic load in COW std::string

The relaxed load is already optimal, checking the __single_threaded
global before doing a non-atomic load isn't an optimization.

libstdc++-v3/ChangeLog:

	* include/bits/cow_string.h (basic_string::_M_is_leaked()):
	Revert change to check __is_single_threaded() before using
	atomic load.
---

diff --git a/libstdc++-v3/include/bits/cow_string.h b/libstdc++-v3/include/bits/cow_string.h
index d6ddf3489d1a..389b39583e47 100644
--- a/libstdc++-v3/include/bits/cow_string.h
+++ b/libstdc++-v3/include/bits/cow_string.h
@@ -207,10 +207,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  // so we need to use an atomic load. However, _M_is_leaked
 	  // predicate does not change concurrently (i.e. the string is either
 	  // leaked or not), so a relaxed load is enough.
-	  if (!__gnu_cxx::__is_single_threaded())
-	    return __atomic_load_n(&this->_M_refcount, __ATOMIC_RELAXED) < 0;
-#endif
+	  return __atomic_load_n(&this->_M_refcount, __ATOMIC_RELAXED) < 0;
+#else
 	  return this->_M_refcount < 0;
+#endif
 	}
 
 	bool