[PATCH] Fix PR89789

[Richard Biener]

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

Richard.

2019-03-25  Richard Biener  <rguenther@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;