std::allocator::deallocate support sized-deallocation

Pass the size to the allocator so that it may optimize deallocation.
This was seen to significantly reduce the work required in jemalloc,
with about 40% reduction in CPU cycles in the free path.

Note jemalloc >= 5.2 is required to fix a crash with 0 sizes.

2019-05-20  Pádraig Brady  <pbrady@fb.com>

	* libstdc++-v3/include/ext/new_allocator.h (deallocate): Pass the size
	to the deallocator with -fsized-deallocation.

From-SVN: r271409

libstdc++-v3/ChangeLog

+2019-05-20  Pádraig Brady  <pbrady@fb.com>
+
+	* libstdc++-v3/include/ext/new_allocator.h (deallocate): Pass the size
+	to the deallocator with -fsized-deallocation.
+
 2019-05-20  Jonathan Wakely  <jwakely@redhat.com>
 
 	* testsuite/experimental/memory_resource/new_delete_resource.cc: Fix

libstdc++-v3/include/ext/new_allocator.h

@@ -116,16 +116,24 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       // __p is not permitted to be a null pointer.
       void
-      deallocate(pointer __p, size_type)
+      deallocate(pointer __p, size_type __t)
       {
 #if __cpp_aligned_new
 	if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
 	  {
-	    ::operator delete(__p, std::align_val_t(alignof(_Tp)));
+	    ::operator delete(__p,
+# if __cpp_sized_deallocation
+			      __t * sizeof(_Tp),
+# endif
+			      std::align_val_t(alignof(_Tp)));
 	    return;
 	  }
 #endif
-	::operator delete(__p);
+	::operator delete(__p
+#if __cpp_sized_deallocation
+			  , __t * sizeof(_Tp)
+#endif
+			 );
       }
 
       size_type