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predict.c (tree_predict_by_opcode): Get the probability for builtin_expect from param builtin_expect_probability.

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* predict.c (tree_predict_by_opcode): Get the probability
        for builtin_expect from param builtin_expect_probability.
        * params.def (BUILTIN_EXPECT_PROBABILITY): New parameter.
        * predict.def (PRED_BUILTIN_EXPECT_RELAXED): Fix comments.
        * doc/invoke.texi: Add documentation for builtin-expect-probability.
        * gcc.target/i386/cold-attribute-2.c: Fix the test by using original
        probability.
        * gcc.dg/tree-ssa/ipa-split-5.c: Ditto.
        * gcc.dg/tree-ssa/ipa-split-6.c: Ditto.

--This li (t)ene, and those below, will be ignored--

M    gcc/params.def
M    gcc/predict.def
M    gcc/ChangeLog
M    gcc/testsuite/gcc.dg/tree-ssa/ipa-split-5.c
M    gcc/testsuite/gcc.dg/tree-ssa/ipa-split-6.c
M    gcc/testsuite/gcc.target/i386/cold-attribute-2.c
M    gcc/predict.c
M    gcc/doc/invoke.texi

From-SVN: r203167
This commit is contained in:
Rong Xu 2013-10-03 17:13:50 +00:00 • committed by Rong Xu
parent 2ef7251f6c
commit 942df7390f
8 changed files with 42 additions and 8 deletions
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12
gcc/ChangeLog
View file

@ -1,3 +1,15 @@
2013-10-03 Rong Xu <xur@google.com>
* predict.c (tree_predict_by_opcode): Get the probability
for builtin_expect from param builtin_expect_probability.
* params.def (BUILTIN_EXPECT_PROBABILITY): New parameter.
* predict.def (PRED_BUILTIN_EXPECT_RELAXED): Fix comments.
* doc/invoke.texi: Add documentation for builtin-expect-probability.
* gcc.target/i386/cold-attribute-2.c: Fix the test by using original
probability.
* gcc.dg/tree-ssa/ipa-split-5.c: Ditto.
* gcc.dg/tree-ssa/ipa-split-6.c: Ditto.
2013-10-03 Marc Glisse <marc.glisse@inria.fr>
PR c++/19476

5
gcc/doc/invoke.texi
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@ -9491,6 +9491,11 @@ The known number of iterations is predicted correctly, while
the unknown number of iterations average to roughly 10. This means that the
loop without bounds appears artificially cold relative to the other one.
@item builtin-expect-probability
Control the probability of the expression having the specified value. This
parameter takes a percentage (i.e. 0 ... 100) as input.
The default probability of 90 is obtained empirically.
@item align-threshold
Select fraction of the maximal frequency of executions of a basic block in

13
gcc/params.def
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@ -398,6 +398,19 @@ DEFPARAM(PARAM_MAX_PREDICTED_ITERATIONS,
"max-predicted-iterations",
"The maximum number of loop iterations we predict statically",
100, 0, 0)
/* This parameter controls the probability of builtin_expect. The default
value is 90%. This empirical value is obtained through the weighted
probability of FDO counters (with the FDO count value as the weight)
in some real world programs:
(1) Google performance test benchmarks: the probability is 0.9081.
(2) Linux 3.3 kernel running Google search workload: the probability
is 0.8717. */
DEFPARAM(BUILTIN_EXPECT_PROBABILITY,
"builtin-expect-probability",
"Set the estimated probability in percentage for builtin expect. The default value is 90% probability.",
90, 0, 100)
DEFPARAM(TRACER_DYNAMIC_COVERAGE_FEEDBACK,
"tracer-dynamic-coverage-feedback",
"The percentage of function, weighted by execution frequency, that must be covered by trace formation. Used when profile feedback is available",

9
gcc/predict.c
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@ -2000,11 +2000,12 @@ tree_predict_by_opcode (basic_block bb)
BITMAP_FREE (visited);
if (val)
{
int percent = PARAM_VALUE (BUILTIN_EXPECT_PROBABILITY);
gcc_assert (percent >= 0 && percent <= 100);
if (integer_zerop (val))
predict_edge_def (then_edge, PRED_BUILTIN_EXPECT, NOT_TAKEN);
else
predict_edge_def (then_edge, PRED_BUILTIN_EXPECT, TAKEN);
return;
percent = 100 - percent;
predict_edge (then_edge, PRED_BUILTIN_EXPECT, HITRATE (percent));
}
/* Try "pointer heuristic."
A comparison ptr == 0 is predicted as false.

5
gcc/predict.def
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@ -57,7 +57,10 @@ DEF_PREDICTOR (PRED_UNCONDITIONAL, "unconditional jump", PROB_ALWAYS,
DEF_PREDICTOR (PRED_LOOP_ITERATIONS, "loop iterations", PROB_ALWAYS,
PRED_FLAG_FIRST_MATCH)
/* Hints dropped by user via __builtin_expect feature. */
/* Hints dropped by user via __builtin_expect feature. Note: the
probability of PROB_VERY_LIKELY is now overwritten by param
builtin_expect_probability with a default value of HITRATE(90).
Refer to param.def for details. */
DEF_PREDICTOR (PRED_BUILTIN_EXPECT, "__builtin_expect", PROB_VERY_LIKELY,
PRED_FLAG_FIRST_MATCH)

2
gcc/testsuite/gcc.dg/tree-ssa/ipa-split-5.c
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@ -1,5 +1,5 @@
/* { dg-do compile { target nonpic } } */
/* { dg-options "-O3 -fdump-tree-fnsplit -fdump-tree-optimized" } */
/* { dg-options "-O3 -fdump-tree-fnsplit -fdump-tree-optimized --param=builtin-expect-probability=100" } */
struct a {int a,b;};
struct a make_me_big (int a);

2
gcc/testsuite/gcc.dg/tree-ssa/ipa-split-6.c
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@ -1,6 +1,6 @@
/* PR tree-optimization/52019 */
/* { dg-do compile } */
/* { dg-options "-O3 -fno-tree-sra -fdump-tree-fnsplit -fdump-tree-optimized" } */
/* { dg-options "-O3 -fno-tree-sra -fdump-tree-fnsplit -fdump-tree-optimized --param=builtin-expect-probability=100" } */
#include "ipa-split-5.c"

2
gcc/testsuite/gcc.target/i386/cold-attribute-2.c
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@ -1,5 +1,5 @@
/* { dg-do compile } */
/* { dg-options "-O2" } */
/* { dg-options "-O2 --param=builtin-expect-probability=100" } */
#include <string.h>
t(int c)
{