https://gcc.gnu.org/bugzilla/show_bug.cgi?id=45215
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |pinskia at gcc dot gnu.org
Component|tree-optimization |middle-end
Status|NEW |ASSIGNED
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
_1 = t_3(D) & 256;
if (_1 != 0)
goto <bb 4>; [1.04%]
else
goto <bb 3>; [98.96%]
<bb 3> [local count: 1062574912]:
<bb 4> [local count: 1073741824]:
# _2 = PHI <-26(2), 0(3)>
So the trick here is that 256 is `0x1<<8` so we want to shift that bit up to
the sign bit and then arthimetic shift down to get 0/-1 and then and with -26.
It seems like we could do this in ifcvt I think.
we do find the block:
IF-THEN-JOIN block found, pass 1, test 2, then 3, join 4
IF-CASE-2 found, start 2, else 3
but we don't optimize it (on aarch64 we use csel).
We could do this on the gimple level with a match pattern.
(simplify
(cond (ne (and @0 integer_pow2p@1) integer_zerop) INTEGER_CST@2 integer_zerop)
....
Maybe only do this late and if shift is cheap (though there is no predicates
for that yet).
