re PR gcov-profile/24487 (Basic block frequencies inaccurate)

	PR profile/24487
	* predict.c (predict_loops): Do not estimate more than
	MAX_PRED_LOOP_ITERATIONS in PRED_LOOP_ITERATIONS heuristic.
	* predict.def (MAX_PRED_LOOP_ITERATIONS): Define.

From-SVN: r106276

gcc/ChangeLog

+2005-10-31  Jan Hubicka  <jh@suse.cz>
+
+	PR profile/24487
+	* predict.c (predict_loops): Do not estimate more than
+	MAX_PRED_LOOP_ITERATIONS in PRED_LOOP_ITERATIONS heuristic.
+	* predict.def (MAX_PRED_LOOP_ITERATIONS): Define.
+
 2005-10-31  Andrew MacLeod  <amacleod@redhat.com>
 	
 	PR tree-optimization/19097

gcc/predict.c

@@ -624,6 +624,8 @@ predict_loops (struct loops *loops_info, bool rtlsimpleloops)
 	      niter = desc.niter + 1;
 	      if (niter == 0)        /* We might overflow here.  */
 		niter = desc.niter;
+	      if (niter > MAX_PRED_LOOP_ITERATIONS)
+		niter = MAX_PRED_LOOP_ITERATIONS;
 
 	      prob = (REG_BR_PROB_BASE
 		      - (REG_BR_PROB_BASE + niter /2) / niter);
@@ -654,13 +656,16 @@ predict_loops (struct loops *loops_info, bool rtlsimpleloops)
 		  if (host_integerp (niter, 1)
 		      && tree_int_cst_lt (niter,
 				          build_int_cstu (NULL_TREE,
-						       REG_BR_PROB_BASE - 1)))
+						 MAX_PRED_LOOP_ITERATIONS - 1)))
 		    {
 		      HOST_WIDE_INT nitercst = tree_low_cst (niter, 1) + 1;
-		      probability = (REG_BR_PROB_BASE + nitercst / 2) / nitercst;
+		      probability = ((REG_BR_PROB_BASE + nitercst / 2)
+				     / nitercst);
 		    }
 		  else
-		    probability = 1;
+		    probability = ((REG_BR_PROB_BASE
+				    + MAX_PRED_LOOP_ITERATIONS / 2)
+				   / MAX_PRED_LOOP_ITERATIONS);
 
 		  predict_edge (exits[j], PRED_LOOP_ITERATIONS, probability);
 		}

gcc/predict.def

@@ -58,6 +58,18 @@ DEF_PREDICTOR (PRED_UNCONDITIONAL, "unconditional jump", PROB_ALWAYS,
 DEF_PREDICTOR (PRED_LOOP_ITERATIONS, "loop iterations", PROB_ALWAYS,
 	       PRED_FLAG_FIRST_MATCH)
 
+/* For guessed profiles, the loops having unknown number of iterations
+   are predicted to iterate relatively few (10) times at average.
+   For functions containing one loop with large known number of iterations
+   and other loops having unbounded loops we would end up predicting all
+   the other loops cold that is not usually the case.  So we need to artifically
+   flatten the profile.  
+
+   We need to cut the maximal predicted iterations to large enought iterations
+   so the loop appears important, but safely within HOT_BB_COUNT_FRACTION
+   range.  */
+#define MAX_PRED_LOOP_ITERATIONS 100
+
 /* Hints dropped by user via __builtin_expect feature.  */
 DEF_PREDICTOR (PRED_BUILTIN_EXPECT, "__builtin_expect", PROB_VERY_LIKELY,
 	       PRED_FLAG_FIRST_MATCH)