Hi,
Current default probably for builtin_expect is 0.9996.
This makes the freq of unlikely bb very low (4), which
suppresses the inlining of any calls within those bb.
We used FDO data to measure the branch probably for
the branch annotated with builtin_expert.
For google
internal benchmarks, the weight average
(the profile count value as the weight) is 0.9081.
Linux kernel is another program that is heavily annotated
with builtin-expert. We measured its weight average as 0.8717,
using google search as
the workload.
This patch sets the alternate hirate probability for
builtin_expert
to 90%. With the alternate hirate, we measured performance
improvement for google
benchmarks and Linux kernel.
-Rong
2013-09-26 Rong Xu <x...@google.com>
* params.def (DEFPARAM): New.
* params.def: New.
* predict.c (tree_predict_by_opcode): Alternate
probablity hirate for builtin_expect.
Index: params.def
===================================================================
--- params.def (revision 202638)
+++ params.def (working copy)
@@ -483,6 +483,10 @@ DEFPARAM(TRACER_MIN_BRANCH_PROBABILITY,
"tracer-min-branch-probability",
"Stop forward growth if the probability of best edge is less than this
threshold (in percent). Used when profile feedback is not available",
50, 0, 100)
+DEFPARAM(BUILTIN_EXPECT_PROBABILITY_RELAXED,
+ "builtin-expect-probability-relaxed",
+ "Set the estimated probability for builtin expect. By default using
PROB_VERY_LIKELY, while value of 1 using HIRATE(90) probability.",
+ 0, 0, 1)
/* The maximum number of incoming edges to consider for crossjumping. */
DEFPARAM(PARAM_MAX_CROSSJUMP_EDGES,
Index: params.def
===================================================================
--- params.def (revision 202638)
+++ params.def (working copy)
@@ -483,6 +483,10 @@ DEFPARAM(TRACER_MIN_BRANCH_PROBABILITY,
"tracer-min-branch-probability",
"Stop forward growth if the probability of best edge is less than this
threshold (in percent). Used when profile feedback is not available",
50, 0, 100)
+DEFPARAM(BUILTIN_EXPECT_PROBABILITY_RELAXED,
+ "builtin-expect-probability-relaxed",
+ "Set the estimated probability for builtin expect. By default using
PROB_VERY_LIKELY, while value of 1 using HIRATE(90) probability.",
+ 0, 0, 1)
/* The maximum number of incoming edges to consider for crossjumping. */
DEFPARAM(PARAM_MAX_CROSSJUMP_EDGES,
Index: predict.c
===================================================================
--- predict.c (revision 202638)
+++ predict.c (working copy)
@@ -1950,10 +1950,17 @@ tree_predict_by_opcode (basic_block bb)
BITMAP_FREE (visited);
if (val)
{
+ enum br_predictor predictor;
+
+ if (PARAM_VALUE (BUILTIN_EXPECT_PROBABILITY_RELAXED) == 0)
+ predictor = PRED_BUILTIN_EXPECT;
+ else
+ predictor = PRED_BUILTIN_EXPECT_RELAXED;
+
if (integer_zerop (val))
- predict_edge_def (then_edge, PRED_BUILTIN_EXPECT, NOT_TAKEN);
+ predict_edge_def (then_edge, predictor, NOT_TAKEN);
else
- predict_edge_def (then_edge, PRED_BUILTIN_EXPECT, TAKEN);
+ predict_edge_def (then_edge, predictor, TAKEN);
return;
}
/* Try "pointer heuristic."
