On Mon, Jan 31, 2022 at 2:13 AM Jakub Jelinek <ja...@redhat.com> wrote:
>
> On Sun, Jan 30, 2022 at 10:16:44AM +0000, Navid Rahimi via Gcc-patches wrote:
> > Thanks Jakob for the correction. Sadly, I didn’t have any access to any non
> > x86 architecture. But x86 was fully tested and there was no regression.
> >
> > In my spare time I will look at implementation of this for short-circuit
> > targets.
>
> Note, it isn't just about those targets.
> If you write the code as:
> _Bool
> g (_Bool a, _Bool b)
> {
> _Bool c;
> if (!a)
> c = 0;
> else if (!b)
> c = 0;
> else
> c = 1;
> return c == (a ^ b);
> }
> instead, it will not match either, not even on x86, even when it is
> equivalent.
>
> Though, maybe for non-short-circuiting targets we should recognize this
> somewhere and turn into c = a & b;
>
> Since phiopt2 it is:
> <bb 2> [local count: 1073741824]:
> if (a_4(D) != 0)
> goto <bb 3>; [50.00%]
> else
> goto <bb 4>; [50.00%]
>
> <bb 3> [local count: 536870913]:
> _8 = (int) b_5(D);
>
> <bb 4> [local count: 1073741824]:
> # iftmp.0_3 = PHI <_8(3), 0(2)>
> and phiopt3 makes
> <bb 2> [local count: 1073741824]:
> if (a_4(D) != 0)
> goto <bb 3>; [50.00%]
> else
> goto <bb 4>; [50.00%]
>
> <bb 3> [local count: 536870913]:
>
> <bb 4> [local count: 1073741824]:
> # _9 = PHI <b_5(D)(3), 0(2)>
> iftmp.0_3 = (int) _9;
> out of that.
>
> CCing Andrew if he'd like to have a look for GCC 13.
Yes I have a patch to recognize:
if (a_3(D) != 0)
goto <bb 4>; [50.00%]
else
goto <bb 3>; [50.00%]
<bb 3> [local count: 536870912]:
<bb 4> [local count: 1073741824]:
# c_2 = PHI <0(3), b_4(D)(2)>
already (a ? b : 0) into a & b.
This is already recorded as PR 89263.
Thanks,
Andrew Pinski
>
> Jakub
>
