[gcc r13-4436] tree-optimization/107935 - fixup equivalence handling in PHI VN

[gcc r13-4436] tree-optimization/107935 - fixup equivalence handling in PHI VN

[Richard Biener]

https://gcc.gnu.org/g:8629f212af0acb113879d0bc45291c54743790f1

commit r13-4436-g8629f212af0acb113879d0bc45291c54743790f1
Author: Richard Biener <rguenther@suse.de>
Date:   Thu Dec 1 09:01:20 2022 +0100

    tree-optimization/107935 - fixup equivalence handling in PHI VN
    
    The following makes sure to honor the backedge processing logic
    that forces VARYING there.
    
            PR tree-optimization/107935
            * tree-ssa-sccvn.cc (visit_phi): Honor forced VARYING on
            backedges.
    
            * gcc.dg/torture/pr107935.c: New testcase.

Diff:
---
 gcc/testsuite/gcc.dg/torture/pr107935.c | 18 ++++++++++++++++++
 gcc/tree-ssa-sccvn.cc                   |  7 ++++++-
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/gcc/testsuite/gcc.dg/torture/pr107935.c b/gcc/testsuite/gcc.dg/torture/pr107935.c
new file mode 100644
index 00000000000..78175100f80
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr107935.c
@@ -0,0 +1,18 @@
+/* { dg-do compile } */
+
+int *a, **b;
+int main() {
+  int d = 0, *e = &d;
+ L:
+  *e = d;
+  if (a) {
+    int *g = e = *b;
+    if (!e)
+      __builtin_abort();
+    if (**b)
+      return 0;
+    *g = 1;
+    goto L;
+  }
+  return 0;
+}
diff --git a/gcc/tree-ssa-sccvn.cc b/gcc/tree-ssa-sccvn.cc
index 1e7763baa38..b9f289b6eca 100644
--- a/gcc/tree-ssa-sccvn.cc
+++ b/gcc/tree-ssa-sccvn.cc
@@ -5840,7 +5840,12 @@ visit_phi (gimple *phi, bool *inserted, bool backedges_varying_p)
 		  continue;
 	      }
 	    /* There's also the possibility to use equivalences.  */
-	    if (!FLOAT_TYPE_P (TREE_TYPE (def)))
+	    if (!FLOAT_TYPE_P (TREE_TYPE (def))
+		/* But only do this if we didn't force any of sameval or
+		   val to VARYING because of backedge processing rules.  */
+		&& (TREE_CODE (sameval) != SSA_NAME
+		    || SSA_VAL (sameval) == sameval)
+		&& (TREE_CODE (def) != SSA_NAME || SSA_VAL (def) == def))
 	      {
 		vn_nary_op_t vnresult;
 		tree ops[2];