[PATCH] Fix PR89789

[Richard Biener]

Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.

Richard.

2019-03-25  Richard Biener  <rguent...@suse.de>

        PR tree-optimization/89789
        * tree-ssa-sccvn.c (set_ssa_val_to): Do not allow lattice
        changes from non-undefined back to undefined.

        * gcc.dg/torture/pr89789.c: New testcase.

Index: gcc/testsuite/gcc.dg/torture/pr89789.c
===================================================================
--- gcc/testsuite/gcc.dg/torture/pr89789.c      (nonexistent)
+++ gcc/testsuite/gcc.dg/torture/pr89789.c      (working copy)
@@ -0,0 +1,23 @@
+/* { dg-do compile } */
+
+int x2;
+
+void
+m2 (void)
+{
+  goto gg;
+
+  int fz, vh = 0;
+
+  for (fz = 0; fz < 1; ++fz)
+    {
+      vh ^= x2;
+
+      if (0)
+       {
+gg:
+         x2 %= 1;
+         x2 += vh;
+       }
+    }
+}
Index: gcc/tree-ssa-sccvn.c
===================================================================
--- gcc/tree-ssa-sccvn.c        (revision 269906)
+++ gcc/tree-ssa-sccvn.c        (working copy)
@@ -3746,10 +3746,13 @@ set_ssa_val_to (tree from, tree to)
            }
          return false;
        }
-      else if (currval != VN_TOP
-              && ! is_gimple_min_invariant (currval)
-              && ! ssa_undefined_value_p (currval, false)
-              && is_gimple_min_invariant (to))
+      bool curr_invariant = is_gimple_min_invariant (currval);
+      bool curr_undefined = (TREE_CODE (currval) == SSA_NAME
+                            && ssa_undefined_value_p (currval, false));
+      if (currval != VN_TOP
+         && !curr_invariant
+         && !curr_undefined
+         && is_gimple_min_invariant (to))
        {
          if (dump_file && (dump_flags & TDF_DETAILS))
            {
@@ -3764,6 +3767,24 @@ set_ssa_val_to (tree from, tree to)
            }
          to = from;
        }
+      else if (currval != VN_TOP
+              && !curr_undefined
+              && TREE_CODE (to) == SSA_NAME
+              && ssa_undefined_value_p (to, false))
+       {
+         if (dump_file && (dump_flags & TDF_DETAILS))
+           {
+             fprintf (dump_file, "Forcing VARYING instead of changing "
+                      "value number of ");
+             print_generic_expr (dump_file, from);
+             fprintf (dump_file, " from ");
+             print_generic_expr (dump_file, currval);
+             fprintf (dump_file, " (non-undefined) to ");
+             print_generic_expr (dump_file, to);
+             fprintf (dump_file, " (undefined)\n");
+           }
+         to = from;
+       }
       else if (TREE_CODE (to) == SSA_NAME
               && SSA_NAME_OCCURS_IN_ABNORMAL_PHI (to))
        to = from;