re PR regression/40886 (No loop counter reversal for simple loops anymore)

Fix PR40886.

2010-02-11  Sebastian Pop  <sebastian.pop@amd.com>
	    Changpeng Fang  <changpeng.fang@amd.com>

	PR middle-end/40886
	* tree-ssa-loop-ivopts.c (determine_use_iv_cost_condition): Decrement
	the cost of an IV candidate when the IV is used in a test against zero.

	* gcc.dg/tree-ssa/ivopts-3.c: New.

Co-Authored-By: Changpeng Fang <changpeng.fang@amd.com>

From-SVN: r156701

gcc/ChangeLog

+2010-02-11  Sebastian Pop  <sebastian.pop@amd.com>
+	    Changpeng Fang  <changpeng.fang@amd.com>
+
+	PR middle-end/40886
+	* tree-ssa-loop-ivopts.c (determine_use_iv_cost_condition): Decrement
+	the cost of an IV candidate when the IV is used in a test against zero.
+
+	* gcc.dg/tree-ssa/ivopts-3.c: New.
+
 2010-02-11  Richard Guenther  <rguenther@suse.de>
 
 	PR lto/41664

gcc/testsuite/gcc.dg/tree-ssa/ivopts-3.c

+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-ivopts-details" } */
+
+void main (void)
+{
+  int i;
+  for (i = 0; i < 10; i++)
+    f2 ();
+}
+
+/* { dg-final { scan-tree-dump-times "!= 0" 4 "ivopts" } }  */
+/* { dg-final { cleanup-tree-dump "ivopts" } }  */

gcc/tree-ssa-loop-ivopts.c

@@ -4089,6 +4089,7 @@ determine_use_iv_cost_condition (struct ivopts_data *data,
   bitmap depends_on_elim = NULL, depends_on_express = NULL, depends_on;
   comp_cost elim_cost, express_cost, cost;
   bool ok;
+  tree *control_var, *bound_cst;
 
   /* Only consider real candidates.  */
   if (!cand->iv)
@@ -4110,9 +4111,21 @@ determine_use_iv_cost_condition (struct ivopts_data *data,
 
   /* Try expressing the original giv.  If it is compared with an invariant,
      note that we cannot get rid of it.  */
-  ok = extract_cond_operands (data, use->stmt, NULL, NULL, NULL, &cmp_iv);
+  ok = extract_cond_operands (data, use->stmt, &control_var, &bound_cst,
+			      NULL, &cmp_iv);
   gcc_assert (ok);
 
+  /* When the condition is a comparison of the candidate IV against
+     zero, prefer this IV.
+
+     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)
+      && (operand_equal_p (*control_var, cand->var_after, 0)
+	  || operand_equal_p (*control_var, cand->var_before, 0)))
+    elim_cost.cost -= 1;
+
   express_cost = get_computation_cost (data, use, cand, false,
 				       &depends_on_express, NULL);
   fd_ivopts_data = data;