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_apinski@quicinc.com>

diff --git a/gcc/testsuite/gcc.dg/torture/pr118922-1.c b/gcc/testsuite/gcc.dg/torture/pr118922-1.c
new file mode 100644 (file)
index 0000000..27e8c78
--- /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 f67f52d2d69abf01b1c5ca1e0c55658c820d54ca..7d2d1696ee70f26a68c64a1e1ba1f8fc32b5e6f7 100644 (file)
--- a/gcc/tree-ssa-phiopt.cc
+++ b/gcc/tree-ssa-phiopt.cc
@@ -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);