On Wed, 5 Jan 2022 at 17:55, Richard Biener <richard.guent...@gmail.com>
wrote:
> On Wed, Jan 5, 2022 at 10:42 AM Jakub Jelinek <ja...@redhat.com> wrote:
> >
> > On Wed, Jan 05, 2022 at 10:38:53AM +0100, Richard Biener via Gcc-patches
> wrote:
> > > On Wed, Jan 5, 2022 at 10:18 AM Zhao Wei Liew <zhaoweil...@gmail.com>
> wrote:
> > > >
> > > > > X >= -1 && X <= 1 is (hopefully?) going to be simplified
> > > > > as (unsigned)X + 1 <= 2, it might be good to simplify it this way
> > > > > here as well?
> > > >
> > > > Yup, GCC does simplify it that way in the end, so I didn't really
> bother to simplify it here. That said, I'm open to simplifying it here as
> well, but I'm not sure how to do the unsigned cast.
> > >
> > > You'd do sth like
> > > (with
> > > { tree utype = unsigned_type_for (type); }
> > > (cond (le (plus (convert:utype @0) { build_one_cst (utype); }) {
> > > build_int_cst (utype, 2); }) ...)
> > >
> > > extra tricky will be 1 bit integer types, I guess it might be easiest
> > > to exclude them
> > > and special case them separately - X / Y is always X for them I think,
> >
> > Note, we already have:
> > /* X / bool_range_Y is X. */
> > (simplify
> > (div @0 SSA_NAME@1)
> > (if (INTEGRAL_TYPE_P (type) && ssa_name_has_boolean_range (@1))
> > @0))
> > for those.
>
> Ah, it might not handle the signed : 1 case though since -1 is not in the
> bool range. We could generalize the above though.
>
> Richard.
>
> >
> > Jakub
> >
>
Perhaps it is possible to exclude 1-bit cases and rely on other existing
simplifications to deal with them?
In particular, GCC seems to already optimally simplify the signed and
unsigned 1-bit cases [1].
[1]:
struct S {
unsigned int x: 1;
int y: 1;
};
unsigned int fu(S s) {
return 1 / s.x;
}
int fi(S s) {
return 1 / s.y;
}
fu(S):
mov eax, 1
ret
fi(S):
mov eax, -1
ret
