Hi Richard,
> -----Original Message-----
> From: Richard Sandiford <richard.sandif...@arm.com>
> Sent: Friday, June 9, 2023 7:08 PM
> To: Kyrylo Tkachov via Gcc-patches <gcc-patches@gcc.gnu.org>
> Cc: Kyrylo Tkachov <kyrylo.tkac...@arm.com>
> Subject: Re: [PATCH] simplify-rtx: Implement constant folding of
> SS_TRUNCATE, US_TRUNCATE
>
> Kyrylo Tkachov via Gcc-patches <gcc-patches@gcc.gnu.org> writes:
> > Hi all,
> >
> > This patch implements RTL constant-folding for the SS_TRUNCATE and
> US_TRUNCATE codes.
> > The semantics are a clamping operation on the argument with the min and
> max of the narrow mode,
> > followed by a truncation. The signedness of the clamp and the min/max
> extrema is derived from
> > the signedness of the saturating operation.
> >
> > We have a number of instructions in aarch64 that use SS_TRUNCATE and
> US_TRUNCATE to represent
> > their operations and we have pretty thorough runtime tests in
> gcc.target/aarch64/advsimd-intrinsics/vqmovn*.c.
> > With this patch the instructions are folded away at optimisation levels and
> the correctness checks still
> > pass.
> >
> > Bootstrapped and tested on aarch64-none-linux-gnu and aarch64_be-none-
> elf.
> > Ok for trunk?
> >
> > Thanks,
> > Kyrill
> >
> > gcc/ChangeLog:
> >
> > * simplify-rtx.cc (simplify_const_unary_operation):
> > Handle US_TRUNCATE, SS_TRUNCATE.
> >
> > diff --git a/gcc/simplify-rtx.cc b/gcc/simplify-rtx.cc
> > index
> 276be67aa67247dd46361ab9badc46ab089d6df0..5983a06e5a8ca89c717e864
> 8be410024147b16e6 100644
> > --- a/gcc/simplify-rtx.cc
> > +++ b/gcc/simplify-rtx.cc
> > @@ -2131,6 +2131,22 @@ simplify_const_unary_operation (enum
> rtx_code code, machine_mode mode,
> > result = wide_int::from (op0, width, UNSIGNED);
> > break;
> >
> > + case US_TRUNCATE:
> > + case SS_TRUNCATE:
> > + {
> > + signop sgn = code == US_TRUNCATE ? UNSIGNED : SIGNED;
> > + wide_int nmax
> > + = wide_int::from (wi::max_value (width, sgn),
> > + GET_MODE_PRECISION (imode), sgn);
> > + wide_int nmin
> > + = wide_int::from (wi::min_value (width, sgn),
> > + GET_MODE_PRECISION (imode), sgn);
> > + result
> > + = wide_int::from (op0, GET_MODE_PRECISION (imode), sgn);
> > + result = wi::min (wi::max (result, nmin, sgn), nmax, sgn);
>
> FWIW, it looks like this could be:
>
> result = wi::min (wi::max (op0, nmin, sgn), nmax, sgn);
>
> without the first assignment to result. That feels more natural IMO,
> since no conversion is being done on op0.Thanks, that works indeed. I'll push the attached patch to trunk once bootstrap and testing completes. Kyrill > > Thanks, > Richard > > > + result = wide_int::from (result, width, sgn); > > + break; > > + } > > case SIGN_EXTEND: > > result = wide_int::from (op0, width, SIGNED); > > break;
sstrunc.patch
Description: sstrunc.patch
