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.

diff --git a/libstdc++-v3/include/bits/atomic_base.h b/libstdc++-v3/include/bits/atomic_base.h
index ebcfeb4..015acef 100644 (file)
--- 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;
       }