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Fix incorrect loop exit edge probability [PR103270]

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r12-4526 cancelled jump thread path rotates loop. It exposes a issue in
profile-estimate when predict_extra_loop_exits, outer loop's exit edge
is marked as inner loop's extra loop exit and set with incorrect
prediction, then a hot inner loop will become cold loop finally through
optimizations, this patch add loop check when searching extra exit edges
to avoid unexpected predict_edge from predict_paths_for_bb.

Regression tested on P8LE.

gcc/ChangeLog:

2021-12-21  Xionghu Luo  <luoxhu@linux.ibm.com>

	PR middle-end/103270
	* predict.c (predict_extra_loop_exits): Add loop parameter.
	(predict_loops): Call with loop argument.

gcc/testsuite/ChangeLog:

2021-12-21  Xionghu Luo  <luoxhu@linux.ibm.com>

	PR middle-end/103270
	* gcc.dg/pr103270.c: New test.
This commit is contained in:
Xionghu Luo 2021-12-20 21:10:09 -06:00
parent 460d53f816
commit 46bfe1b0e1
2 changed files with 25 additions and 4 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

10
gcc/predict.c
View file

@ -1859,7 +1859,7 @@ predict_iv_comparison (class loop *loop, basic_block bb,
exits to predict them using PRED_LOOP_EXTRA_EXIT. */
static void
predict_extra_loop_exits (edge exit_edge)
predict_extra_loop_exits (class loop *loop, edge exit_edge)
{
unsigned i;
bool check_value_one;
@ -1912,12 +1912,14 @@ predict_extra_loop_exits (edge exit_edge)
continue;
if (EDGE_COUNT (e->src->succs) != 1)
{
predict_paths_leading_to_edge (e, PRED_LOOP_EXTRA_EXIT, NOT_TAKEN);
predict_paths_leading_to_edge (e, PRED_LOOP_EXTRA_EXIT, NOT_TAKEN,
loop);
continue;
}
FOR_EACH_EDGE (e1, ei, e->src->preds)
predict_paths_leading_to_edge (e1, PRED_LOOP_EXTRA_EXIT, NOT_TAKEN);
predict_paths_leading_to_edge (e1, PRED_LOOP_EXTRA_EXIT, NOT_TAKEN,
loop);
}
}
@ -2008,7 +2010,7 @@ predict_loops (void)
ex->src->index, ex->dest->index);
continue;
}
predict_extra_loop_exits (ex);
predict_extra_loop_exits (loop, ex);
if (number_of_iterations_exit (loop, ex, &niter_desc, false, false))
niter = niter_desc.niter;

19
gcc/testsuite/gcc.dg/pr103270.c Normal file
View file

@ -0,0 +1,19 @@
/* { dg-do compile } */
/* { dg-options "-O2 -fdump-tree-profile_estimate" } */
void test(int a, int* i)
{
for (; a < 5; ++a)
{
int b = 0;
int c = 0;
for (; b != -11; b--)
for (int d = 0; d ==0; d++)
{
*i += c & a;
c = b;
}
}
}
/* { dg-final { scan-tree-dump-not "extra loop exit heuristics of edge\[^:\]*:" "profile_estimate"} } */