Hello.
During investigation of an IVOPTs issue, I noticed that tree-ssa-loop-ivopts.c
uses a hard-coded
constant AVG_LOOP_NITER. Very similar constant can be seen in cfgloopanal.c.
Thus, I've changed
that to a new param.
Apart from that, I would like to change the default value to 10.
As numbers of SPEC CPU2006 show:
Loop count: 18236
avg. # of iter: 11908.46
median # of iter: 10.00
avg. (1% cutoff) # of iter: 1003.87
avg. (5% cutoff) # of iter: 449.78
avg. (10% cutoff) # of iter: 209.46
avg. (20% cutoff) # of iter: 62.24
avg. (30% cutoff) # of iter: 42.69
Even though the average number of loop iteration is quite high, let's start to
increase it
conservatively to 10. Benchmark results are within a noise level (-Ofast runs
faster by 0.47%).
Patch survives regression tests and bootstraps on x86_64-linux-gnu.
Ready for trunk?
Thanks,
Martin
>From 604637de550a9d23b8a509cdbf493a7212a186f0 Mon Sep 17 00:00:00 2001
From: marxin <mli...@suse.cz>
Date: Tue, 21 Jun 2016 14:52:31 +0200
Subject: [PATCH] Introduce new param: AVG_LOOP_NITER
gcc/ChangeLog:
2016-06-21 Martin Liska <mli...@suse.cz>
* params.def: Add avg-loop niter.
* tree-ssa-loop-ivopts.c (avg_loop_niter): Use the param.
* cfgloopanal.c (expected_loop_iterations_unbounded): Likewise.
---
gcc/cfgloopanal.c | 9 ++++-----
gcc/params.def | 5 +++++
gcc/tree-ssa-loop-ivopts.c | 7 +++----
3 files changed, 12 insertions(+), 9 deletions(-)
diff --git a/gcc/cfgloopanal.c b/gcc/cfgloopanal.c
index c163986..2739f44 100644
--- a/gcc/cfgloopanal.c
+++ b/gcc/cfgloopanal.c
@@ -241,10 +241,9 @@ expected_loop_iterations_unbounded (const struct loop *loop,
if (read_profile_p)
*read_profile_p = false;
- /* Average loop rolls about 3 times. If we have no profile at all, it is
- best we can do. */
+ /* If we have no profile at all, use AVG_LOOP_NITER. */
if (profile_status_for_fn (cfun) == PROFILE_ABSENT)
- expected = 3;
+ expected = PARAM_VALUE (PARAM_AVG_LOOP_NITER);
else if (loop->latch->count || loop->header->count)
{
gcov_type count_in, count_latch;
@@ -282,9 +281,9 @@ expected_loop_iterations_unbounded (const struct loop *loop,
if (freq_in == 0)
{
- /* If we have no profile at all, expect 3 iterations. */
+ /* If we have no profile at all, use AVG_LOOP_NITER iterations. */
if (!freq_latch)
- expected = 3;
+ expected = PARAM_VALUE (PARAM_AVG_LOOP_NITER);
else
expected = freq_latch * 2;
}
diff --git a/gcc/params.def b/gcc/params.def
index 894b7f3..b86d592 100644
--- a/gcc/params.def
+++ b/gcc/params.def
@@ -527,6 +527,11 @@ DEFPARAM(PARAM_IV_ALWAYS_PRUNE_CAND_SET_BOUND,
"If number of candidates in the set is smaller, we always try to remove unused ivs during its optimization.",
10, 0, 0)
+DEFPARAM(PARAM_AVG_LOOP_NITER,
+ "avg-loop-niter",
+ "Average number of iterations of a loop.",
+ 10, 1, 0)
+
DEFPARAM(PARAM_SCEV_MAX_EXPR_SIZE,
"scev-max-expr-size",
"Bound on size of expressions used in the scalar evolutions analyzer.",
diff --git a/gcc/tree-ssa-loop-ivopts.c b/gcc/tree-ssa-loop-ivopts.c
index 6b403f5..d401c41 100644
--- a/gcc/tree-ssa-loop-ivopts.c
+++ b/gcc/tree-ssa-loop-ivopts.c
@@ -115,8 +115,6 @@ along with GCC; see the file COPYING3. If not see
/* The infinite cost. */
#define INFTY 10000000
-#define AVG_LOOP_NITER(LOOP) 5
-
/* Returns the expected number of loop iterations for LOOP.
The average trip count is computed from profile data if it
exists. */
@@ -128,8 +126,9 @@ avg_loop_niter (struct loop *loop)
if (niter == -1)
{
niter = likely_max_stmt_executions_int (loop);
- if (niter == -1 || niter > AVG_LOOP_NITER (loop))
- return AVG_LOOP_NITER (loop);
+
+ if (niter == -1 || niter > PARAM_VALUE (PARAM_AVG_LOOP_NITER))
+ return PARAM_VALUE (PARAM_AVG_LOOP_NITER);
}
return niter;
--
2.8.4
