diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index e897d5032f0..741d19f33d4 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2008-08-21  Richard Guenther  <rguenther@suse.de>
+
+	* tree-ssa-pre.c (insert_into_preds_of_block): Before inserting
+	a PHI ask VN if it is already available.
+	* tree-ssa-sccvn.h (vn_phi_lookup): Declare.
+	* tree-ssa-sccvn.c (vn_phi_lookup): Export.
+
 2008-08-21  Richard Guenther  <rguenther@suse.de>
 
 	PR middle-end/36817
diff --git a/gcc/tree-ssa-pre.c b/gcc/tree-ssa-pre.c
index d2a55ae7ddc..606cafa1792 100644
--- a/gcc/tree-ssa-pre.c
+++ b/gcc/tree-ssa-pre.c
@@ -2896,7 +2896,7 @@ insert_into_preds_of_block (basic_block block, unsigned int exprnum,
   pre_expr eprime;
   edge_iterator ei;
   tree type = get_expr_type (expr);
-  tree temp;
+  tree temp, res;
   gimple phi;
 
   if (dump_file && (dump_flags & TDF_DETAILS))
@@ -3051,12 +3051,8 @@ insert_into_preds_of_block (basic_block block, unsigned int exprnum,
   if (TREE_CODE (type) == COMPLEX_TYPE
       || TREE_CODE (type) == VECTOR_TYPE)
     DECL_GIMPLE_REG_P (temp) = 1;
-  phi = create_phi_node (temp, block);
 
-  gimple_set_plf (phi, NECESSARY, false);
-  VN_INFO_GET (gimple_phi_result (phi))->valnum = gimple_phi_result (phi);
-  VN_INFO (gimple_phi_result (phi))->value_id = val;
-  VEC_safe_push (gimple, heap, inserted_exprs, phi);
+  phi = create_phi_node (temp, block);
   FOR_EACH_EDGE (pred, ei, block->preds)
     {
       pre_expr ae = avail[pred->src->index];
@@ -3067,6 +3063,20 @@ insert_into_preds_of_block (basic_block block, unsigned int exprnum,
       else
 	add_phi_arg (phi, PRE_EXPR_NAME (avail[pred->src->index]), pred);
     }
+  /* If the PHI node is already available, use it.  */
+  if ((res = vn_phi_lookup (phi)) != NULL_TREE)
+    {
+      gimple_stmt_iterator gsi = gsi_for_stmt (phi);
+      remove_phi_node (&gsi, true);
+      release_defs (phi);
+      add_to_value (val, get_or_alloc_expr_for_name (res));
+      return false;
+    }
+
+  gimple_set_plf (phi, NECESSARY, false);
+  VN_INFO_GET (gimple_phi_result (phi))->valnum = gimple_phi_result (phi);
+  VN_INFO (gimple_phi_result (phi))->value_id = val;
+  VEC_safe_push (gimple, heap, inserted_exprs, phi);
 
   newphi = get_or_alloc_expr_for_name (gimple_phi_result (phi));
   add_to_value (val, newphi);
diff --git a/gcc/tree-ssa-sccvn.c b/gcc/tree-ssa-sccvn.c
index 26a65f126e1..0b995d6837d 100644
--- a/gcc/tree-ssa-sccvn.c
+++ b/gcc/tree-ssa-sccvn.c
@@ -1458,7 +1458,7 @@ static VEC(tree, heap) *shared_lookup_phiargs;
    value number if it exists in the hash table.  Return NULL_TREE if
    it does not exist in the hash table. */
 
-static tree
+tree
 vn_phi_lookup (gimple phi)
 {
   void **slot;
diff --git a/gcc/tree-ssa-sccvn.h b/gcc/tree-ssa-sccvn.h
index 49baa761831..84f096ef224 100644
--- a/gcc/tree-ssa-sccvn.h
+++ b/gcc/tree-ssa-sccvn.h
@@ -184,6 +184,7 @@ vn_reference_t vn_reference_insert (tree, tree, VEC (tree, gc) *);
 vn_reference_t vn_reference_insert_pieces (VEC (tree, gc) *,
 					   VEC (vn_reference_op_s, heap) *,
 					   tree, unsigned int);
+tree vn_phi_lookup (gimple);
 
 hashval_t vn_nary_op_compute_hash (const vn_nary_op_t);
 int vn_nary_op_eq (const void *, const void *);