RE: [PATCH v2] x86: Allow minus ones for Kn and standard constants for XMMn

> -----Original Message-----
> From: H.J. Lu <[email protected]>
> Sent: Friday, August 21, 2026 12:03 PM
> To: Hongtao Liu <[email protected]>
> Cc: GCC Patches <[email protected]>; Uros Bizjak
> <[email protected]>; Liu, Hongtao <[email protected]>
> Subject: [PATCH v2] x86: Allow minus ones for Kn and standard constants for
> XMMn
> 
> On Fri, Aug 21, 2026 at 10:06 AM Hongtao Liu <[email protected]> wrote:
> >
> > On Fri, Aug 21, 2026 at 9:08 AM H.J. Lu <[email protected]> wrote:
> > >
> > > Since we can load minus ones into an SSE or MASK register, allow
> > > minus ones for SSE and MASK registers so that
> > >
> >
> > I think we should use standard_sse_constant_p (x, mode) for
> > MAYBE_SSE_CLASS_P since there's no direct instruction to move -1 to
> > sse register for scalar floating mode, pcmpeq is only used for vector
> > mode.
> > So how about
> >
> > if (CONSTANT_P (x))
> >   {
> >     if (MAYBE_MAAX_CLASS_P (regclass))
> >       return NO_REGS;
> >     if (MAYBE_MASK_CLASS_P (regclass))
> >       return x == constm1_rtx ? regclass : NO_REG;
> >     if (MAYBE_SSE_CLASS_P (regclass))
> >       return (mode != VOIDmode && stardard_sse_constant_p (x, mode)) ?
> > regclass : NO_REGS;
> > }
> 
> Like this?
Ok.

> 
> --
> H.J.
> ---
> Since we can load minus ones into a MASK register and standard SSE
> constants into a SSE register, allow them for MASK and SSE registers so that
> 
> kxnor %k0, %k0, %k0
> 
> is used to load -1 into mask register, instead of loading from memory.
> 
> PR target/126959
> * config/i386/i386.cc (ix86_preferred_reload_class): Allow minus ones for
> MASK register and standard SSE constants for SSE register.
> * gcc.target/i386/pr126959-1a.c: New test.
> * gcc.target/i386/pr126959-1b.c: Likewise.
> * gcc.target/i386/pr126959-2a.c: Likewise.
> * gcc.target/i386/pr126959-2b.c: Likewise.