On 22/05/15 16:29 +0200, Jakub Jelinek wrote:
On Fri, May 22, 2015 at 03:15:10PM +0100, Jonathan Wakely wrote:
--- a/libstdc++-v3/include/ext/aligned_buffer.h
+++ b/libstdc++-v3/include/ext/aligned_buffer.h
@@ -31,21 +31,23 @@
#pragma GCC system_header
-#if __cplusplus >= 201103L
-# include <type_traits>
-#else
+#if __cplusplus < 201103L
# include <bits/c++0x_warning.h>
#endif
+#include <cstddef>
+
namespace __gnu_cxx
{
template<typename _Tp>
struct __aligned_buffer
- : std::aligned_storage<sizeof(_Tp), std::alignment_of<_Tp>::value>
{
- typename
- std::aligned_storage<sizeof(_Tp), std::alignment_of<_Tp>::value>::type
- _M_storage;
+ // Target macro ADJUST_FIELD_ALIGN can produce different alignment for
+ // types when used as class members. __aligned_buffer is intended for
+ // use as a class member, so align the buffer as for a class member.
+ struct _Tp2 { _Tp _M_t; };
+
+ alignas(alignof(_Tp2)) unsigned char _M_storage[sizeof(_Tp)];
Is alignof(_Tp2) always the same as alignof(_Tp2::_M_t) on all targets
(I mean, won't some target align the structure more than its only field)?
Hmm, maybe. I don't know.
Wouldn't it be safer to use alignof(_Tp2::_M_t) here?
Yes.
Though, apparently that is a GNU extension, so you'd need to use __alignof__
instead.
Yes, that's what I did in an earlier version of the patch, so I'll go
back to that.
