https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80197
Uroš Bizjak <ubizjak at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2017-03-27
CC| |jakub at gcc dot gnu.org,
| |rguenth at gcc dot gnu.org
Ever confirmed|0 |1
--- Comment #1 from Uroš Bizjak <ubizjak at gmail dot com> ---
For some reason, recently fixed if-conversion (PR79389) does not trigger in PGO
case. There is still a jump with -O2:
mulsd %xmm0, %xmm5
mulsd %xmm2, %xmm2
addsd %xmm2, %xmm5
ucomisd %xmm5, %xmm4
jb .L17
.L16:
addl $1, %ebp
.L17:
addl $1, %edi
cmpl %edi, %ebx
je .L5
Since this asm corresponds to random operands, the jump can't be predicted:
for (count=0; count<Num_samples; count++)
{
double x= Random_nextDouble(R);
double y= Random_nextDouble(R);
if ( x*x + y*y <= 1.0)
under_curve ++;
}
Based on the discussion in PR79389, and the fact that -O2 and -O3 both compile
to a jump, I suspect that loop splitting cost model should be fine tuned to
also handle PGO case. Note that
Adding some CCs.
