[m-rev.] diff: fix GCC labels with GCC 4.9 on x86_64

[Julien Fischer]

On Thu, 19 Feb 2015, Zoltan Somogyi wrote:

>
>
> On Thu, 19 Feb 2015 09:14:43 +1100 (AEDT), Julien Fischer <jfischer at opturion.com> wrote:
>>      Disable GCC's -ftree-dominator-opts optimization when using
>>      GCC 4.9 on the x86_64 and x86.  As with GCC 4.8, its use seems
>>      incompatible with our use of GCC labels.
>
> Wouldn't it be safer to check whether the C compiler accepts
> -ftree-dominator-opts, and disable the option if it does?
> That way, we won't have to repeat this for 4.10, 4.11 etc.
> If the option does respect our use of gcc labels in some
> gcc versions, then those versions could be whitelisted,
> but effectively whitelisting unknown future versions
> seems unwise.

You're right, we should (and will) do that.  I want to first check
whether the issue stil occurs in upstream GCC though.  When this problem
originally occurred I was -- perhaps unwisely -- hoping that it was a
problem that was isolated to 4.8, that doesn't seem to be the case :-(

Cheers,
Julien.