[Bug c/47796] The code to write to a bit_field data strucuture will be removed unexpectedly with gcc 4.5.1 -O2 option

[qihua.dai at intel dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47796

qihua.dai at intel dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |UNCONFIRMED
         Resolution|INVALID                     |

--- Comment #3 from qihua.dai at intel dot com 2011-02-21 04:58:48 UTC ---
(In reply to comment #1)
> You are violating C/C++ aliasing rules:
> pData = (unsigned int *)pTmp;
>         data = *pData;
>         printf("data = 0x%x\n", data);
> You access a tmp_t via an unsigned int which is undefined.

If it's not a bug, why is there the different behavior for -O0 and -O2