https://gcc.gnu.org/g:0d931663498d2f95fb7ea0ae0ef8473f88eed26a
commit r14-11613-g0d931663498d2f95fb7ea0ae0ef8473f88eed26a
Author: Andrew Pinski <quic_apin...@quicinc.com>
Date: Sat Mar 8 22:43:54 2025 -0800
phiopt: Fix value_replacement for middle bb having phi nodes [PR118922]
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_apin...@quicinc.com>
(cherry picked from commit 7232c005afb5002cdfd0a2dbd0e8b8f2d80250ce)
Diff:
---
gcc/testsuite/gcc.dg/torture/pr118922-1.c | 57 +++++++++++++++++++++++++++++++
gcc/tree-ssa-phiopt.cc | 4 +++
2 files changed, 61 insertions(+)
diff --git a/gcc/testsuite/gcc.dg/torture/pr118922-1.c
b/gcc/testsuite/gcc.dg/torture/pr118922-1.c
new file mode 100644
index 000000000000..27e8c78c0e4e
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr118922-1.c
@@ -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);
+}
diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc
index fa8dc2c8a4e3..14bb8442a395 100644
--- a/gcc/tree-ssa-phiopt.cc
+++ b/gcc/tree-ssa-phiopt.cc
@@ -1195,6 +1195,10 @@ 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;
+
gcond *cond = as_a <gcond *> (*gsi_last_bb (cond_bb));
code = gimple_cond_code (cond);
