RE: [PATCH]: issue warning about -f(no-)strict-aliasing in function optimize attribute

["Bingfeng Mei" <bmei at broadcom dot com>]

Then it will warn in following situation

__attribute__ ((optimize (-O2))
void foo()
{
}

And the file itself is compiled as -O1. There are several
tests like that. Should I adopt your suggestion and modify
those tests then? 

Cheers,
Bingfeng. 

> -----Original Message-----
> From: Richard Guenther [mailto:richard.guenther@gmail.com]
> Sent: 10 November 2010 16:55
> To: Bingfeng Mei
> Cc: gcc-patches@gcc.gnu.org
> Subject: Re: [PATCH]: issue warning about -f(no-)strict-aliasing in
> function optimize attribute
> 
> On Wed, Nov 10, 2010 at 5:43 PM, Bingfeng Mei <bmei@broadcom.com> wrote:
> > Hello,
> > Currently, if we specify a different -f(no-)strict-aliasing option
> > in function optimize attribute. GCC just quietly ignores it.
> > http://gcc.gnu.org/ml/gcc/2010-11/msg00091.html It is error-prone as
> > it is not expected by a programmer.
> >
> > The patch issues a warning in such situation. One thing I am not sure
> is that
> > different optimizing levels also have different setting for strict-
> aliasing.
> > Should I also warn that (will make some existing tests fail), or make
> it
> > an exception? This patch ignores such case.
> >
> > Bootstrapped and tested with x86_64-unknown-linux-gnu.
> >
> > Thanks,
> > Bingfeng Mei
> >
> >
> > 2010-11-10 ?Bingfeng Mei ?<bmei@broadcom.com>
> > ? ? ? ?* c-family/c-common.c (parse_optimize_options): Issue warning
> about
> > ? ? ? ?-f(no-)strict-aliasing in optimize attribute.
> >
> >
> > Index: c-family/c-common.c
> > ===================================================================
> > --- c-family/c-common.c (revision 166523)
> > +++ c-family/c-common.c (working copy)
> > @@ -7808,6 +7808,16 @@ parse_optimize_options (tree args, bool
> >
> > ? targetm.override_options_after_change();
> >
> > + ?/* Currently GCC doesn't support function-specific -f(no-)strict-
> aliasing
> > + ? ?Issue a warning under such case.
> > + ? ?Ignore cases where difference is caused by different
> optimization
> > + ? ?levels. (strict aliasing is disabled < -O2 )
> > + ?*/
> > + ?if ((!flag_strict_aliasing && saved_flag_strict_aliasing &&
> optimize >= 2)
> > + ? ? || (flag_strict_aliasing && !saved_flag_strict_aliasing &&
> optimize < 2))
> > + ? ?warning (OPT_Wattributes,
> > + ? ? ? ? ? ? "-f(no-)strict-aliasing option in optimize attribute
> ignored");
> > +
> > ? /* Don't allow changing -fstrict-aliasing. ?*/
> > ? flag_strict_aliasing = saved_flag_strict_aliasing;
> 
> I think an easier test is
> 
>    if (flag_strict_aliasing != saved_flag_strict_aliasing)
>      warning (OPT_Wattributes,
>                   "changes in strict-aliasing behavior ignored");
> 
> or sth like that.
> 
> Richard.
> 
> >