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tree-optimization/99694 - fix value-numbering PHIs

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This avoids endless cycling when a PHI node with unchanged backedge
value (the PHI result appearing there) is subject to CSE since doing
that effectively alters the hash entry.  The way to avoid this is
to ignore such edges when processing the PHI node.

2021-03-22  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/99694
	* tree-ssa-sccvn.c (visit_phi): Ignore edges with the
	PHI result.

	* gcc.dg/torture/pr99694.c: New testcase.
This commit is contained in:
Richard Biener 2021-03-22 11:09:46 +01:00
parent c4519fe3db
commit b931e4792b
2 changed files with 29 additions and 0 deletions
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27
gcc/testsuite/gcc.dg/torture/pr99694.c Normal file
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@ -0,0 +1,27 @@
/* { dg-do compile } */
/* { dg-additional-options "-w" } */
#include <stdint.h>
int a, b, c;
void d() {
uint16_t e;
int32_t *f;
int32_t *g;
if (a) {
int32_t *k;
for (;; *k += 1) {
int32_t **i = &f;
int32_t **l = &g;
for (e = 6; e; e++) {
g = k = f;
j:
**l = 0;
}
*i = c;
}
}
uint16_t i = &e;
b = i / 0;
goto j;
}

2
gcc/tree-ssa-sccvn.c
View File

@ -5199,6 +5199,8 @@ visit_phi (gimple *phi, bool *inserted, bool backedges_varying_p)
{
tree def = PHI_ARG_DEF_FROM_EDGE (phi, e);
if (def == PHI_RESULT (phi))
continue;
++n_executable;
if (TREE_CODE (def) == SSA_NAME)
{