From 32e55402bb0fc442831d775a516f2def4f948f93 Mon Sep 17 00:00:00 2001
From: rguenth <rguenth@138bc75d-0d04-0410-961f-82ee72b054a4>
Date: Thu, 12 May 2011 14:08:00 +0000
Subject: [PATCH] 2011-05-12  Richard Guenther  <rguenther@suse.de>

        Backport from mainline
        2011-05-02  Richard Guenther  <rguenther@suse.de>

	PR tree-optimization/48822
	* tree-ssa-sccvn.c (set_ssa_val_to): Never go up the lattice.
	(process_scc): Indicate which iteration we start.

	* gcc.dg/torture/pr48822.c: New testcase.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/branches/gcc-4_6-branch@173705 138bc75d-0d04-0410-961f-82ee72b054a4

index be253f4..81b52db 100644
new file mode 100644
index 0000000..b619f36
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr48822.c
@@ -0,0 +1,20 @@
+/* { dg-do compile } */
+
+void foo (int *, int *);
+int bar ()
+{
+  int a = 0;
+  int b = 0;
+  if (b != 0)
+    {
+      int ax = a;
+      int bx = b;
+      while (bx != 0)
+	{
+	  int tem = ax % bx;
+	  ax = bx;
+	  bx = tem;
+	}
+    }
+  foo (&a, &b);
+}
diff --git a/gcc/tree-ssa-sccvn.c b/gcc/tree-ssa-sccvn.c
index 9222cb5..eb88969 100644
--- a/gcc/tree-ssa-sccvn.c
+++ b/gcc/tree-ssa-sccvn.c
@@ -2103,12 +2103,26 @@ print_scc (FILE *out, VEC (tree, heap) *scc)
 static inline bool
 set_ssa_val_to (tree from, tree to)
 {
-  tree currval;
+  tree currval = SSA_VAL (from);
 
-  if (from != to
-      && TREE_CODE (to) == SSA_NAME
-      && SSA_NAME_OCCURS_IN_ABNORMAL_PHI (to))
-    to = from;
+  if (from != to)
+    {
+      if (currval == from)
+	{
+	  if (dump_file && (dump_flags & TDF_DETAILS))
+	    {
+	      fprintf (dump_file, "Not changing value number of ");
+	      print_generic_expr (dump_file, from, 0);
+	      fprintf (dump_file, " from VARYING to ");
+	      print_generic_expr (dump_file, to, 0);
+	      fprintf (dump_file, "\n");
+	    }
+	  return false;
+	}
+      else if (TREE_CODE (to) == SSA_NAME
+	       && SSA_NAME_OCCURS_IN_ABNORMAL_PHI (to))
+	to = from;
+    }
 
   /* The only thing we allow as value numbers are VN_TOP, ssa_names
      and invariants.  So assert that here.  */
@@ -2125,8 +2139,6 @@ set_ssa_val_to (tree from, tree to)
       print_generic_expr (dump_file, to, 0);
     }
 
-  currval = SSA_VAL (from);
-
   if (currval != to  && !operand_equal_p (currval, to, OEP_PURE_SAME))
     {
       VN_INFO (from)->valnum = to;
@@ -3124,6 +3136,8 @@ process_scc (VEC (tree, heap) *scc)
     {
       changed = false;
       iterations++;
+      if (dump_file && (dump_flags & TDF_DETAILS))
+	fprintf (dump_file, "Starting iteration %d\n", iterations);
       /* As we are value-numbering optimistically we have to
 	 clear the expression tables and the simplified expressions
 	 in each iteration until we converge.  */
-- 
1.7.0.4