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[committed] libstdc++: Strip cv-qualifiers in std::atomic<FP> (PR 95282)

Message ID 20200616213540.GA1535367@redhat.com
State New
Headers show
Series [committed] libstdc++: Strip cv-qualifiers in std::atomic<FP> (PR 95282) | expand

Commit Message

Jonathan Wakely June 16, 2020, 9:35 p.m. UTC 
This improves the previous fix for PR 95282, and extends it to also
apply to the exchange function (which has a similar problem and would
become ill-formed with my proposed fix for PR 95378).

	PR libstdc++/95282
	* include/bits/atomic_base.h (__atomic_impl::load): Use the _Val
	alias instead of deducing _Tp as an unqualified type.
	(__atomic_impl::exchange): Use the _Val alias to remove volatile
	from the reinterpret_cast result type.

Tested powerpc64le-linux, committed to master.
commit e40b11a91cb345db1324c3cb8f75b01e28056693
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Jun 16 22:34:55 2020 +0100

    libstdc++: Strip cv-qualifiers in std::atomic<FP> (PR 95282)
    
    This improves the previous fix for PR 95282, and extends it to also
    apply to the exchange function (which has a similar problem and would
    become ill-formed with my proposed fix for PR 95378).
    
            PR libstdc++/95282
            * include/bits/atomic_base.h (__atomic_impl::load): Use the _Val
            alias instead of deducing _Tp as an unqualified type.
            (__atomic_impl::exchange): Use the _Val alias to remove volatile
            from the reinterpret_cast result type.
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Patch

diff --git a/libstdc++-v3/include/bits/atomic_base.h b/libstdc++-v3/include/bits/atomic_base.h
index ebcfeb4d51a..015acef83c4 100644
--- a/libstdc++-v3/include/bits/atomic_base.h
+++ b/libstdc++-v3/include/bits/atomic_base.h
@@ -870,21 +870,21 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
       { __atomic_store(__ptr, std::__addressof(__t), int(__m)); }
 
     template<typename _Tp>
-      _GLIBCXX_ALWAYS_INLINE _Tp
-      load(const volatile _Tp* __ptr, memory_order __m) noexcept
+      _GLIBCXX_ALWAYS_INLINE _Val<_Tp>
+      load(const _Tp* __ptr, memory_order __m) noexcept
       {
 	alignas(_Tp) unsigned char __buf[sizeof(_Tp)];
-	_Tp* __dest = reinterpret_cast<_Tp*>(__buf);
+	auto* __dest = reinterpret_cast<_Val<_Tp>*>(__buf);
 	__atomic_load(__ptr, __dest, int(__m));
 	return *__dest;
       }
 
     template<typename _Tp>
-      _GLIBCXX_ALWAYS_INLINE _Tp
+      _GLIBCXX_ALWAYS_INLINE _Val<_Tp>
       exchange(_Tp* __ptr, _Val<_Tp> __desired, memory_order __m) noexcept
       {
         alignas(_Tp) unsigned char __buf[sizeof(_Tp)];
-	_Tp* __dest = reinterpret_cast<_Tp*>(__buf);
+	auto* __dest = reinterpret_cast<_Val<_Tp>*>(__buf);
 	__atomic_exchange(__ptr, std::__addressof(__desired), __dest, int(__m));
 	return *__dest;
       }