2013-10-11  Rong Xu  <xur@google.com>

	* predict.c (tree_predict_by_opcode): Bump the 
        estimiated probability if builtin_expect expression is
        in loop exit test.

Index: predict.c
===================================================================
--- predict.c	(revision 203462)
+++ predict.c	(working copy)
@@ -1951,7 +1951,31 @@ tree_predict_by_opcode (basic_block bb)
   if (val)
     {
       int percent = PARAM_VALUE (BUILTIN_EXPECT_PROBABILITY);
+      void **preds;
 
+      /* This handles the cases like
+           while (__builtin_expect (exp, 1)) { ... }
+         W/o builtin_expect, the default HITRATE is 91%.
+	 It does not make sense to estimate a lower probability of 90%
+	 (current default for builtin_expect) with the annotation.
+	 So here, we bump the probability by a small amount.  */
+      preds = pointer_map_contains (bb_predictions, bb);
+      if (preds)
+        {
+          struct edge_prediction *pred;
+
+          for (pred = (struct edge_prediction *) *preds; pred;
+	       pred = pred->ep_next)
+	    {
+	      if (pred->ep_predictor == PRED_LOOP_EXIT
+		  && predictor_info [(int) PRED_LOOP_EXIT].hitrate
+		     > HITRATE (percent))
+		percent += 4;
+	      if (percent > 100)
+		percent = 100;
+	    }
+	}
+
       gcc_assert (percent >= 0 && percent <= 100);
       if (integer_zerop (val))
         percent = 100 - percent;