[adjusted to apply after pr15256-2-pr18041 rather than before <mikpe@it.uu.se>]

From 21a41ea517c2e60d3a910aca8012a2c0d57b1005 Mon Sep 17 00:00:00 2001
From: Peter A. Bigot <pabigot@users.sourceforge.net>
Date: Thu, 22 Sep 2011 09:22:25 -0500
Subject: [PATCH] SF 3412886 pre-patch pr50213/tree-optimization

This is a back-port of the following upstream commit.

commit cd22a7968a89e465b934b7b2b9ff685a9652601b
Author: rguenth <rguenth@138bc75d-0d04-0410-961f-82ee72b054a4>
Date:   Wed Sep 7 11:28:39 2011 +0000

    2011-09-07  Richard Guenther  <rguenther@suse.de>

        PR tree-optimization/50213
        * tree-flow.h (simple_iv_increment_p): Declare.
        * tree-ssa-dom.c (simple_iv_increment_p): Export.  Also handle
        POINTER_PLUS_EXPR.
        * tree-ssa-forwprop.c (ssa_forward_propagate_and_combine): Do
        not propagate simple IV counter increments.

--- gcc-4.6.2/gcc/tree-flow.h.~1~	2011-05-11 15:07:54.000000000 +0200
+++ gcc-4.6.2/gcc/tree-flow.h	2012-01-14 15:11:07.000000000 +0100
@@ -601,6 +601,7 @@ extern void dump_dominator_optimization_
 extern void debug_dominator_optimization_stats (void);
 int loop_depth_of_name (tree);
 tree degenerate_phi_result (gimple);
+bool simple_iv_increment_p (gimple);
 
 /* In tree-ssa-copy.c  */
 extern void propagate_value (use_operand_p, tree);
--- gcc-4.6.2/gcc/tree-ssa-dom.c.~1~	2011-06-30 21:35:45.000000000 +0200
+++ gcc-4.6.2/gcc/tree-ssa-dom.c	2012-01-14 15:11:07.000000000 +0100
@@ -1396,9 +1396,10 @@ record_equality (tree x, tree y)
    i_1 = phi (..., i_2)
    i_2 = i_1 +/- ...  */
 
-static bool
+bool
 simple_iv_increment_p (gimple stmt)
 {
+  enum tree_code code;
   tree lhs, preinc;
   gimple phi;
   size_t i;
@@ -1410,12 +1411,13 @@ simple_iv_increment_p (gimple stmt)
   if (TREE_CODE (lhs) != SSA_NAME)
     return false;
 
-  if (gimple_assign_rhs_code (stmt) != PLUS_EXPR
-      && gimple_assign_rhs_code (stmt) != MINUS_EXPR)
+  code = gimple_assign_rhs_code (stmt);
+  if (code != PLUS_EXPR
+      && code != MINUS_EXPR
+      && code != POINTER_PLUS_EXPR)
     return false;
 
   preinc = gimple_assign_rhs1 (stmt);
-
   if (TREE_CODE (preinc) != SSA_NAME)
     return false;
 
--- gcc-4.6.2/gcc/tree-ssa-forwprop.c.~1~	2012-01-14 15:07:18.000000000 +0100
+++ gcc-4.6.2/gcc/tree-ssa-forwprop.c	2012-01-14 15:11:07.000000000 +0100
@@ -2262,10 +2262,12 @@ tree_ssa_forward_propagate_single_use_va
 		  else
 		    gsi_next (&gsi);
 		}
-	      else if (code == POINTER_PLUS_EXPR
-		       && can_propagate_from (stmt))
+	      else if (code == POINTER_PLUS_EXPR)
 		{
-		  if (TREE_CODE (gimple_assign_rhs2 (stmt)) == INTEGER_CST
+		  tree off = gimple_assign_rhs2 (stmt);
+		  if (TREE_CODE (off) == INTEGER_CST
+		      && can_propagate_from (stmt)
+		      && !simple_iv_increment_p (stmt)
 		      /* ???  Better adjust the interface to that function
 			 instead of building new trees here.  */
 		      && forward_propagate_addr_expr
@@ -2277,7 +2279,7 @@ tree_ssa_forward_propagate_single_use_va
 						 rhs,
 						 fold_convert
 						   (ptr_type_node,
-						    gimple_assign_rhs2 (stmt))))))
+						    off)))))
 		    {
 		      release_defs (stmt);
 		      todoflags |= TODO_remove_unused_locals;