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phiopt: Fix value_replacement for middle bb having phi nodes [PR118922]

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After r12-5300-gf98f373dd822b3, value_replacement would be able to look at the
following cfg structure:
```
  <bb 5> [local count: 1014686024]:
  if (h_6 != 0)
    goto <bb 7>; [94.50%]
  else
    goto <bb 6>; [5.50%]

  <bb 6> [local count: 114863530]:
  # h_6 = PHI <0(4), 1(5)>

  <bb 7> [local count: 1073741824]:
  # f_8 = PHI <0(5), h_6(6)>
  _9 = f_8 ^ 1;
  a.0_10 = a;
  _11 = _9 + a.0_10;
  if (_11 != -117)
    goto <bb 5>; [94.50%]
  else
    goto <bb 8>; [5.50%]
```

value_replacement would incorrectly think the middle bb (6) was empty and so it decides
to remove condition in bb5 and replacing it with 0 as the function thought it was `h_6 ? 0 : h_6`.
But since the there is an incoming phi node to bb6 defining h_6 that is incorrect.

The fix is to check if there is phi nodes in the middle bb and set empty_or_with_defined_p to false.
This was not needed before r12-5300-gf98f373dd822b3 because the phi would have been dead otherwise due to
other checks.

Bootstrapped and tested on x86_64-linux-gnu.

	PR tree-optimization/118922

gcc/ChangeLog:

	* tree-ssa-phiopt.cc (value_replacement): Set empty_or_with_defined_p
	to false when there is phi nodes for the middle bb.

gcc/testsuite/ChangeLog:

	* gcc.dg/torture/pr118922-1.c: New test.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>
This commit is contained in:
Andrew Pinski
2025-03-08 22:43:54 -08:00
parent 1b21da6abf
commit 7232c005af
2 changed files with 61 additions and 0 deletions
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57
gcc/testsuite/gcc.dg/torture/pr118922-1.c Normal file
View File

@@ -0,0 +1,57 @@
/* { dg-do run } */
/* PR tree-optimization/118922 */
/* Phi-opt would convert:
<bb 5> [local count: 1014686024]:
if (h_6 != 0)
goto <bb 7>; [94.50%]
else
goto <bb 6>; [5.50%]
<bb 6> [local count: 114863530]:
# h_6 = PHI <0(4), 1(5)>
<bb 7> [local count: 1073741824]:
# f_8 = PHI <0(5), h_6(6)>
_9 = f_8 ^ 1;
a.0_10 = a;
_11 = _9 + a.0_10;
if (_11 != -117)
goto <bb 5>; [94.50%]
else
goto <bb 8>; [5.50%]
into:
<bb 4> [local count: 59055799]:
c = d_3;
<bb 5> [local count: 1073741824]:
# f_8 = PHI <0(5), 0(4)>
_9 = f_8 ^ 1;
a.0_10 = a;
_11 = _9 + a.0_10;
if (_11 != -117)
goto <bb 5>; [94.50%]
else
goto <bb 6>; [5.50%]
as it thought the middle bb was empty as there was only a phi node there. */
int a = -117, b, c, e;
void g(int h) {
int f = 0;
while (!f + a - -117) {
f = h == 0;
if (h == 0)
h = 1;
}
}
int main() {
int d = 8;
for (; e;)
d = 0;
c = d;
g(0);
}

4
gcc/tree-ssa-phiopt.cc
View File

@@ -1331,6 +1331,10 @@ value_replacement (basic_block cond_bb, basic_block middle_bb,
empty_or_with_defined_p = false;
}
/* The middle bb is not empty if there are any phi nodes. */
if (phi_nodes (middle_bb))
empty_or_with_defined_p = false;
/* We need to know which is the true edge and which is the false
edge so that we know if have abs or negative abs. */
extract_true_false_edges_from_block (cond_bb, &true_edge, &false_edge);