Re: [PATCH] i386: [APX] Document inline asm behavior and new switch for APX

[Hongtao Liu <crazylht@gmail.com>]

On Thu, Jan 11, 2024 at 7:06 AM Andi Kleen <ak@linux.intel.com> wrote:
>
> Hongtao Liu <crazylht@gmail.com> writes:
> >>
> >> +@opindex mapx-inline-asm-use-gpr32
> >> +@item -mapx-inline-asm-use-gpr32
> >> +When APX_F enabled, EGPR usage was by default disabled to prevent
> >> +unexpected EGPR generation in instructions that does not support it.
> >> +To invoke EGPR usage in inline asm, use this switch to allow EGPR in
> >> +inline asm, while user should ensure the asm actually supports EGPR.
> > Please align with
> > https://gcc.gnu.org/pipermail/gcc-patches/2024-January/642228.html.
> > Ok after changing that.
>
> BTW I think we would need a way to specify this individually per inline
> asm statement too.
>
> Otherwise a library which wants to use APX inline asm in the header
> never can do so until all its users set the option, which will be
> awkward to deploy.
>
> Perhaps it could be a magic clobber string.
We do have new constraints string for gpr32 or gpr16 for registers,
but not for memory due to restrictiction of GCC RA infrastructure
which assumes universal BASE_REG_CLASS/INDEX_REG_CLASS for all inline
asm.
>
> -andi



-- 
BR,
Hongtao