[backport from gcc-4.7/trunk <mikpe@it.uu.se>]

gcc/

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-4.6.1/gcc/tree-flow.h.~1~	2011-05-11 15:07:54.000000000 +0200
+++ gcc-4.6.1/gcc/tree-flow.h	2011-09-23 12:07:16.000000000 +0200
@@ -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-4.6.1/gcc/tree-ssa-dom.c.~1~	2011-02-14 18:59:10.000000000 +0100
+++ gcc-4.6.1/gcc/tree-ssa-dom.c	2011-09-23 12:07:16.000000000 +0200
@@ -1397,9 +1397,10 @@ 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;
@@ -1411,12 +1412,13 @@ 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-4.6.1/gcc/tree-ssa-forwprop.c.~1~	2011-04-22 20:53:30.000000000 +0200
+++ gcc-4.6.1/gcc/tree-ssa-forwprop.c	2011-09-23 12:05:40.000000000 +0200
@@ -1995,6 +1995,7 @@ tree_ssa_forward_propagate_single_use_va
 		       && can_propagate_from (stmt))
 		{
 		  if (TREE_CODE (gimple_assign_rhs2 (stmt)) == INTEGER_CST
+		      && !simple_iv_increment_p (stmt)
 		      /* ???  Better adjust the interface to that function
 			 instead of building new trees here.  */
 		      && forward_propagate_addr_expr