re PR libstdc++/54005 (Use __atomic_always_lock_free in libstdc++ is_lock_free…

re PR libstdc++/54005 (Use __atomic_always_lock_free in libstdc++ is_lock_free instead of __atomic_is_lock_free)

	PR libstdc++-v3/54005
	* include/bits/atomic_base.h (__atomic_base<_TTp>::is_lock_free(),
	__atomic_base<_PTp*>::is_lock_free()): Call __atomic_always_lock_free
	with the type-derived _S_alignment instead of __alignof the object.
	* include/std/atomic (atomic<T>::is_lock_free()): Likewise.

From-SVN: r266018

libstdc++-v3/ChangeLog

+2018-11-11  Hans-Peter Nilsson  <hp@axis.com>
+
+	PR libstdc++-v3/54005
+	* include/bits/atomic_base.h (__atomic_base<_TTp>::is_lock_free(),
+	__atomic_base<_PTp*>::is_lock_free()): Call __atomic_always_lock_free
+	with the type-derived _S_alignment instead of __alignof the object.
+	* include/std/atomic (atomic<T>::is_lock_free()): Likewise.
+
 2018-11-11  Jonathan Wakely  <jwakely@redhat.com>
 
 	Implement P0318R1 unwrap_ref_decay and unwrap_reference

libstdc++-v3/include/bits/atomic_base.h

@@ -355,7 +355,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       {
 	// Use a fake, minimally aligned pointer.
 	return __atomic_is_lock_free(sizeof(_M_i),
-	    reinterpret_cast<void *>(-__alignof(_M_i)));
+	    reinterpret_cast<void *>(-_S_alignment));
       }
 
       bool
@@ -363,7 +363,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       {
 	// Use a fake, minimally aligned pointer.
 	return __atomic_is_lock_free(sizeof(_M_i),
-	    reinterpret_cast<void *>(-__alignof(_M_i)));
+	    reinterpret_cast<void *>(-_S_alignment));
       }
 
       _GLIBCXX_ALWAYS_INLINE void

libstdc++-v3/include/std/atomic

@@ -222,7 +222,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       {
 	// Produce a fake, minimally aligned pointer.
 	return __atomic_is_lock_free(sizeof(_M_i),
-	    reinterpret_cast<void *>(-__alignof(_M_i)));
+	    reinterpret_cast<void *>(-_S_alignment));
       }
 
       bool
@@ -230,7 +230,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       {
 	// Produce a fake, minimally aligned pointer.
 	return __atomic_is_lock_free(sizeof(_M_i),
-	    reinterpret_cast<void *>(-__alignof(_M_i)));
+	    reinterpret_cast<void *>(-_S_alignment));
       }
 
 #if __cplusplus >= 201703L