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.
Jakub
