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tree-optimization/100492 - avoid irreducible regions in loop distribution

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When we distribute away a condition we rely on the ability to
change it to either 1 != 0 or 0 != 0 depending on the direction
of the exit branch in the respective loop.  But when the loop
contains an irreducible sub-region then for the conditions inside
this this fails and can lead to infinite loops being generated.

Avoid distibuting loops with irreducible sub-regions.

2021-05-10  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/100492
	* tree-loop-distribution.c (find_seed_stmts_for_distribution):
	Find nothing when the loop contains an irreducible region.

	* gcc.dg/torture/pr100492.c: New testcase.
This commit is contained in:
Richard Biener 2021-05-10 11:37:27 +02:00
parent cc1d563887
commit 60af2db180
2 changed files with 36 additions and 0 deletions
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26
gcc/testsuite/gcc.dg/torture/pr100492.c Normal file
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@ -0,0 +1,26 @@
/* { dg-do run } */
/* { dg-additional-options "-ftree-loop-distribution" } */
extern void abort (void);
signed char a, c;
int b, d, *e = &d, g;
signed static char f;
int main() {
int h = 0;
int a_ = a;
for (; a_ < 1; a = ++a_) {
int *i[5], **j = &i[4], ***k[3][2] = {{&j}}, ****l = &k[2][1], *****m = &l;
char *n = &c;
f = *e = g = 0;
for (; g < 2; g++) {
for (b = 0; b < 3; b++)
h = (h && (*n = 0)) == 0;
if (g)
break;
}
}
if (f != 0)
abort ();
return 0;
}

10
gcc/tree-loop-distribution.c
View file

@ -3203,6 +3203,16 @@ find_seed_stmts_for_distribution (class loop *loop, vec<gimple *> *work_list)
/* Initialize the worklist with stmts we seed the partitions with. */
for (unsigned i = 0; i < loop->num_nodes; ++i)
{
/* In irreducible sub-regions we don't know how to redirect
conditions, so fail. See PR100492. */
if (bbs[i]->flags & BB_IRREDUCIBLE_LOOP)
{
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file, "loop %d contains an irreducible region.\n",
loop->num);
work_list->truncate (0);
break;
}
for (gphi_iterator gsi = gsi_start_phis (bbs[i]);
!gsi_end_p (gsi); gsi_next (&gsi))
{