| Message ID | 7FB04A5C213E9943A72EE127DB74F0ADA69190944C@SJEXCHCCR02.corp.ad.broadcom.com |
|---|---|
| State | New |
| Headers | show |
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. >
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.
>
> >
On Wed, Nov 10, 2010 at 6:30 PM, Bingfeng Mei <bmei@broadcom.com> wrote: > 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? Hmm. I suppose we could instead check saved_flag_strict_aliasing && !flag_strict_aliasing, thus assume it's safe to not enable strict-aliasing even when asked to and only refrain from silently ignoring disabling of strict aliasing. Richard. > 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. >> >> > > > >
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;