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peel-1.c: New testcase.

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* gcc.dg/tree-prof/peel-1.c: New testcase.
	* loop-unroll.c (decide_peel_simple): Simple peeling makes sense even
	with simple loops; bound number of branches only when FDO is not
	available.
	(decide_unroll_stupid): Mention that num_loop_branches heuristics
	is off.

From-SVN: r192718
This commit is contained in:
Jan Hubicka 2012-10-23 15:15:58 +00:00
parent 2dc34a12e3
commit 6acf25e4b3
4 changed files with 51 additions and 16 deletions
gcc
ChangeLogloop-unroll.c
testsuite
ChangeLog
gcc.dg/tree-prof
peel-1.c

8
gcc/ChangeLog

@ -1,3 +1,11 @@
2012-10-23 Jan Hubicka <jh@suse.cz>
* loop-unroll.c (decide_peel_simple): Simple peeling makes sense even
with simple loops; bound number of branches only when FDO is not
available.
(decide_unroll_stupid): Mention that num_loop_branches heuristics
is off.
2012-10-23 Nick Clifton <nickc@redhat.com>
PR target/54660

28
gcc/loop-unroll.c

@ -1228,7 +1228,6 @@ static void
decide_peel_simple (struct loop *loop, int flags)
{
unsigned npeel;
struct niter_desc *desc;
double_int iterations;
if (!(flags & UAP_PEEL))
@ -1253,20 +1252,17 @@ decide_peel_simple (struct loop *loop, int flags)
return;
}
/* Check for simple loops. */
desc = get_simple_loop_desc (loop);
/* Check number of iterations. */
if (desc->simple_p && !desc->assumptions && desc->const_iter)
{
if (dump_file)
fprintf (dump_file, ";; Loop iterates constant times\n");
return;
}
/* Do not simply peel loops with branches inside -- it increases number
of mispredicts. */
if (num_loop_branches (loop) > 1)
of mispredicts.
Exception is when we do have profile and we however have good chance
to peel proper number of iterations loop will iterate in practice.
TODO: this heuristic needs tunning; while for complette unrolling
the branch inside loop mostly eliminates any improvements, for
peeling it is not the case. Also a function call inside loop is
also branch from branch prediction POV (and probably better reason
to not unroll/peel). */
if (num_loop_branches (loop) > 1
&& profile_status != PROFILE_READ)
{
if (dump_file)
fprintf (dump_file, ";; Not peeling, contains branches\n");
@ -1435,7 +1431,9 @@ decide_unroll_stupid (struct loop *loop, int flags)
}
/* Do not unroll loops with branches inside -- it increases number
of mispredicts. */
of mispredicts.
TODO: this heuristic needs tunning; call inside the loop body
is also relatively good reason to not unroll. */
if (num_loop_branches (loop) > 1)
{
if (dump_file)

6
gcc/testsuite/ChangeLog

@ -1,7 +1,11 @@
2012-10-23 Jan Hubicka <jh@suse.cz>
* gcc.dg/tree-prof/peel-1.c: New testcase.
2012-10-23 Dominique d'Humieres <dominiq@lps.ens.fr>
PR gcc/52945
* testsuite/gcc.dg/lto/pr52634_0.c: skip the test on Darwin.
* gcc.dg/lto/pr52634_0.c: skip the test on Darwin.
2012-10-23 Joseph Myers <joseph@codesourcery.com>

25
gcc/testsuite/gcc.dg/tree-prof/peel-1.c Normal file

@ -0,0 +1,25 @@
/* { dg-options "-O3 -fdump-rtl-loop2_unroll -fno-unroll-loops -fpeel-loops" } */
void abort();
int a[1000];
int
__attribute__ ((noinline))
t()
{
int i;
for (i=0;i<1000;i++)
if (!a[i])
return 1;
abort ();
}
main()
{
int i;
for (i=0;i<1000;i++)
t();
return 0;
}
/* { dg-final-use { scan-rtl-dump "Considering simply peeling loop" "loop2_unroll" } } */
/* In fact one peeling is enough; we however mispredict number of iterations of the loop
at least until loop_ch is schedule ahead of profiling pass. */
/* { dg-final-use { cleanup-rtl-dump "Decided to simply peel the loop 2 times" } } */