Fix PR43209: Do not decrease the cost of an IV candidate when the cost is infinite.

2010-03-03  Changpeng Fang  <changpeng.fang@amd.com>

      PR middle-end/43209
      * tree-ssa-loop-ivopts.c (determine_use_iv_cost_condition): Do not decrease
      the cost of an IV candidate when the cost is infinite.

      * gcc.dg/tree-ssa/ivopts-4.c: New.

From-SVN: r157217

gcc/ChangeLog

+2010-03-04  Changpeng Fang  <changpeng.fang@amd.com>
+
+      PR middle-end/43209
+      * tree-ssa-loop-ivopts.c (determine_use_iv_cost_condition): Do not decrease
+      the cost of an IV candidate when the cost is infinite.
+
 2010-03-04  Ralf Wildenhues  <Ralf.Wildenhues@gmx.de>
 
 	* doc/extend.texi (Vector Extensions, X86 Built-in Functions):

gcc/testsuite/ChangeLog

+2010-03-04  Changpeng Fang  <changpeng.fang@amd.com>
+
+      PR middle-end/43209
+      * gcc.dg/tree-ssa/ivopts-4.c: New.
+
 2010-03-03  Janis Johnson  <janis187@us.ibm.com>
 
 	* lib/target-supports-dg.exp (check-flags): Provide defaults for

gcc/testsuite/gcc.dg/tree-ssa/ivopts-4.c

+/* { dg-do compile } */
+/* { dg-options "-O1" } */
+void foo(int *p, long i, int j)
+{
+  do {
+      p[i]++;
+  } while (i += j);
+}

gcc/tree-ssa-loop-ivopts.c

 /* Induction variable optimizations.
-   Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009
+   Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010
    Free Software Foundation, Inc.
 
 This file is part of GCC.
@@ -4121,7 +4121,8 @@ determine_use_iv_cost_condition (struct ivopts_data *data,
      TODO: The constant that we're substracting from the cost should
      be target-dependent.  This information should be added to the
      target costs for each backend.  */
-  if (integer_zerop (*bound_cst)
+  if (!infinite_cost_p (elim_cost) /* Do not try to decrease infinite! */
+      && integer_zerop (*bound_cst)
       && (operand_equal_p (*control_var, cand->var_after, 0)
 	  || operand_equal_p (*control_var, cand->var_before, 0)))
     elim_cost.cost -= 1;