Re: [PATCH 02/24] tcg: Use tcg_gen_negsetcond_*

[Richard Henderson]

On 8/8/23 08:55, Peter Maydell wrote:
> On Tue, 8 Aug 2023 at 04:13, Richard Henderson
> <richard.henderson@linaro.org> wrote:
> > Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> > ---
> >   tcg/tcg-op-gvec.c | 6 ++----
> >   tcg/tcg-op.c      | 6 ++----
> >   2 files changed, 4 insertions(+), 8 deletions(-)
> >
> > diff --git a/tcg/tcg-op-gvec.c b/tcg/tcg-op-gvec.c
> > index a062239804..e260a07c61 100644
> > --- a/tcg/tcg-op-gvec.c
> > +++ b/tcg/tcg-op-gvec.c
> > @@ -3692,8 +3692,7 @@ static void expand_cmp_i32(uint32_t dofs, uint32_t aofs, 
> > uint32_t bofs,
> >       for (i = 0; i < oprsz; i += 4) {
> >           tcg_gen_ld_i32(t0, cpu_env, aofs + i);
> >           tcg_gen_ld_i32(t1, cpu_env, bofs + i);
> > -        tcg_gen_setcond_i32(cond, t0, t0, t1);
> > -        tcg_gen_neg_i32(t0, t0);
> > +        tcg_gen_negsetcond_i32(cond, t0, t0, t1);
> >           tcg_gen_st_i32(t0, cpu_env, dofs + i);
> >       }
>
> Is it not possible for the optimizer to notice "you did
> a setcond followed by a neg, let me turn it into negsetcond
> for you" ?

Not at present, no.  That sort of peephole optimization is a bit more difficult than what 
we do at present.


r~