[PATCH] tree-optimization/107935 - fixup equivalence handling in PHI VN

[Richard Biener via Gcc-patches]

The following makes sure to honor the backedge processing logic
that forces VARYING there.

Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.

        PR tree-optimization/107935
        * tree-ssa-sccvn.cc (visit_phi): Honor forced VARYING on
        backedges.

        * gcc.dg/torture/pr107935.c: New testcase.
---
 gcc/testsuite/gcc.dg/torture/pr107935.c | 18 ++++++++++++++++++
 gcc/tree-ssa-sccvn.cc                   |  7 ++++++-
 2 files changed, 24 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.dg/torture/pr107935.c

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 6895ae84d13..fa2f65df159 100644
--- a/gcc/tree-ssa-sccvn.cc
+++ b/gcc/tree-ssa-sccvn.cc
@@ -5861,7 +5861,12 @@ 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];
-- 
2.35.3