Re: [PATCH V2 2/2] [x86] x86: Add a new option -mdaz-ftz to enable FTZ and DAZ flags in MXCSR.

[Hongtao Liu <crazylht@gmail.com>]

On Thu, May 4, 2023 at 5:49 PM Richard Biener
<richard.guenther@gmail.com> wrote:
>
> On Thu, May 4, 2023 at 7:37 AM Hongtao Liu via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
> >
> > On Thu, May 4, 2023 at 1:35 PM Hongtao Liu <crazylht@gmail.com> wrote:
> > >
> > > On Thu, Dec 22, 2022 at 4:04 PM Uros Bizjak <ubizjak@gmail.com> wrote:
> > > >
> > > > On Thu, Dec 22, 2022 at 5:40 AM Hongtao Liu <crazylht@gmail.com> wrote:
> > > > >
> > > > > On Thu, Dec 22, 2022 at 6:46 AM Jakub Jelinek <jakub@redhat.com> wrote:
> > > > > >
> > > > > > On Wed, Dec 21, 2022 at 02:43:43PM -0800, H.J. Lu wrote:
> > > > > > > > > > > > >  Target RejectNegative
> > > > > > > > > > > > >  Set 80387 floating-point precision to 80-bit.
> > > > > > > > > > > > >
> > > > > > > > > > > > > +mdaz-ftz
> > > > > > > > > > > > > +Target
> > > > > > > > > > > >
> > > > > > > > > > > > s/Target/Driver/
> > > > > > > > > > > Change to Driver and Got error like:cc1: error: command-line option
> > > > > > > > > > > ‘-mdaz-ftz’ is valid for the driver but not for C.
> > > > > > > > > > Hi Jakub:
> > > > > > > > > >   I didn't find a good solution to handle this error after changing
> > > > > > > > > > *Target* to *Driver*, Could you give some hints how to solve this
> > > > > > > > > > problem?
> > > > > > > > > > Or is it ok for you to mark this as *Target*(there won't be any save
> > > > > > > > > > and restore in cfun since there's no variable defined here.)
> > > > > > > > >
> > > > > > > > > Since all -m* options are passed to cc1, -mdaz-ftz can't be marked
> > > > > > > > > as Driver.  We need to give it a different name to mark it as Driver.
> > > > > > > >
> > > > > > > > It is ok like that.
> > > > > > > >
> > > > > > > >         Jakub
> > > > > > > >
> > > > > > >
> > > > > > > The GCC driver handles -mno-XXX automatically for -mXXX.  Use
> > > > > > > a different name needs to handle the negation.   Or we can do something
> > > > > > > like this to check for CL_DRIVER before passing it to cc1.
> > > > > >
> > > > > > I meant I'm ok with -m{,no-}daz-ftz option being Target rather than Driver.
> > > > > >
> > > > > Thanks.
> > > > > Uros, Is the patch for you?
> > > >
> > > > The original patch is then OK.
> > > Some users found the -mdaz-ftz option to be very useful, and want it
> > > to be backport to GCC12 and GCC11.
> > > But the patch is not a bugfix one, so i'd like to ask options from
> > s/options/opinions/g
> > > other maintainers, if the patch is suitable for backport?
> > >
> > > The backport patches include both this one and [1] which apply
> > > -mdaz-ftz to all other x86 targets.
> > >
> > > [1] https://gcc.gnu.org/pipermail/gcc-patches/2023-January/610053.html
>
> Please make sure to not backport the -ffast-math linker spec change though.
> Also note the 12 branch is currently frozen.
You're meaning don't backport -shared part since it will cause
different behavior between different backends. ?
I'm trying to backport the daz-ftz part, it won't change the existed
behavior for fast-math or shared.
%{mdaz-ftz:crtfastmath.o%s;Ofast|ffast-math|funsafe-math-optimizations:%{!mno-daz-ftz:crtfastmath.o%s}}
>
> I'll defer to x86 maintainers on the -mdaz-ftz flag itself.
>
> Richard.
>
> > > >
> > > > Thanks,
> > > > Uros.
> > >
> > >
> > >
> > > --
> > > BR,
> > > Hongtao
> >
> >
> >
> > --
> > BR,
> > Hongtao



-- 
BR,
Hongtao