On Thu, Dec 10, 2020 at 12:14:22PM +0100, Eric Botcazou wrote:
> > 2020-12-10 Jakub Jelinek <ja...@redhat.com>
> >
> > PR rtl-optimization/98212
> > * dojump.c (do_compare_rtx_and_jump): Change computation of
> > first_prob for and_them and don't invert prob around it.
> >
> > * gcc.dg/predict-8.c: Adjust expected probability.
> >
> > --- gcc/dojump.c.jj 2020-12-09 15:11:17.042888002 +0100
> > +++ gcc/dojump.c 2020-12-09 20:05:59.535234206 +0100
> > @@ -1148,9 +1148,8 @@ do_compare_rtx_and_jump (rtx op0, rtx op
> > if (and_them)
> > {
> > rtx_code_label *dest_label;
> > - prob = prob.invert ();
> > - profile_probability first_prob = prob.split
> (cprob).invert ();
> > - prob = prob.invert ();
> > + profile_probability first_prob
> > + = prob.split (cprob.invert ()).invert ();
> > /* If we only jump if true, just bypass the second
> jump. */
> > if (! if_false_label)
> > {
>
> The computation looks plausible, but you need to fix the comment too, it is
> rather confusing as it seems to depict an OR-ELSE rather than an AND-THEN.
So like:
2020-12-10 Jakub Jelinek <ja...@redhat.com>
PR rtl-optimization/98212
* dojump.c (do_compare_rtx_and_jump): Change computation of
first_prob for and_them and don't invert prob around it.
* gcc.dg/predict-8.c: Adjust expected probability.
--- gcc/dojump.c.jj 2020-12-09 15:11:17.042888002 +0100
+++ gcc/dojump.c 2020-12-10 12:24:56.991844956 +0100
@@ -1138,19 +1138,21 @@ do_compare_rtx_and_jump (rtx op0, rtx op
cprob = cprob.apply_scale (99, 100);
else
cprob = profile_probability::even ();
- /* We want to split:
+ /* For and_them we want to split:
if (x) goto t; // prob;
+ goto f;
into
- if (a) goto t; // first_prob;
+ if (a) ; else goto f; // first_prob for ;
+ // 1 - first_prob for goto f;
if (b) goto t; // prob;
+ goto f;
such that the overall probability of jumping to t
- remains the same and first_prob is prob * cprob. */
+ remains the same and first_prob is 1 - prob * (1 - cprob). */
if (and_them)
{
rtx_code_label *dest_label;
- prob = prob.invert ();
- profile_probability first_prob = prob.split (cprob).invert ();
- prob = prob.invert ();
+ profile_probability first_prob
+ = prob.split (cprob.invert ()).invert ();
/* If we only jump if true, just bypass the second jump. */
if (! if_false_label)
{
@@ -1163,6 +1170,15 @@ do_compare_rtx_and_jump (rtx op0, rtx op
do_compare_rtx_and_jump (op0, op1, first_code, unsignedp,
mode,
size, dest_label, NULL, first_prob);
}
+ /* For !and_them we want to split:
+ if (x) goto t; // prob;
+ goto f;
+ into
+ if (a) goto t; // first_prob;
+ if (b) goto t; // prob;
+ goto f;
+ such that the overall probability of jumping to t
+ remains the same and first_prob is prob * cprob. */
else
{
profile_probability first_prob = prob.split (cprob);
--- gcc/testsuite/gcc.dg/predict-8.c.jj 2020-01-12 11:54:37.506396918 +0100
+++ gcc/testsuite/gcc.dg/predict-8.c 2020-12-10 10:34:00.632123682 +0100
@@ -8,4 +8,4 @@ int foo(float a, float b) {
return 2;
}
-/* { dg-final { scan-rtl-dump-times "65.\[34]. .guessed" 2 "expand"} } */
+/* { dg-final { scan-rtl-dump-times "99.\[345]. .guessed" 2 "expand"} } */
Jakub
