[committed] libstdc++: Fix atomic<FP>::load (PR 95282)

[Jonathan Wakely]

	PR libstdc++/95282
	* include/bits/atomic_base.h (__atomic_impl::load): Add
	cv-qualifiers to parameter so that _Tp is deduced as the
	unqualified type.
	* testsuite/29_atomics/atomic_float/95282.cc: New test.

Tested powerpc64le-linbux, committed to master.

Backport to gcc-10 to follow.

I've added this testcase to my out-of-testsuite clang tests.


-------------- next part --------------
commit bbaec68c86f8e89a3460cc022c75d4c4179bfb0a
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed May 27 22:55:21 2020 +0100

    libstdc++: Fix atomic<FP>::load (PR 95282)
    
            PR libstdc++/95282
            * include/bits/atomic_base.h (__atomic_impl::load): Add
            cv-qualifiers to parameter so that _Tp is deduced as the
            unqualified type.
            * testsuite/29_atomics/atomic_float/95282.cc: New test.

diff --git a/libstdc++-v3/include/bits/atomic_base.h b/libstdc++-v3/include/bits/atomic_base.h
index 3b66b040976..01f77a0f372 100644
--- a/libstdc++-v3/include/bits/atomic_base.h
+++ b/libstdc++-v3/include/bits/atomic_base.h
@@ -871,7 +871,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
     template<typename _Tp>
       _GLIBCXX_ALWAYS_INLINE _Tp
-      load(_Tp* __ptr, memory_order __m) noexcept
+      load(const volatile _Tp* __ptr, memory_order __m) noexcept
       {
 	alignas(_Tp) unsigned char __buf[sizeof(_Tp)];
 	_Tp* __dest = reinterpret_cast<_Tp*>(__buf);
diff --git a/libstdc++-v3/testsuite/29_atomics/atomic_float/95282.cc b/libstdc++-v3/testsuite/29_atomics/atomic_float/95282.cc
new file mode 100644
index 00000000000..2de751c6ad4
--- /dev/null
+++ b/libstdc++-v3/testsuite/29_atomics/atomic_float/95282.cc
@@ -0,0 +1,35 @@
+// Copyright (C) 2020 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <atomic>
+
+float
+test01()
+{
+  std::atomic<float> a;
+  return a.load();
+}
+
+float
+test02()
+{
+  volatile std::atomic<float> a;
+  return a.load();
+}