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* [Bug middle-end/35343] New: Sum-reduction loop not recognized
@ 2008-02-24 4:28 xinliangli at gmail dot com
2008-02-24 21:56 ` [Bug middle-end/35343] " rguenth at gcc dot gnu dot org
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: xinliangli at gmail dot com @ 2008-02-24 4:28 UTC (permalink / raw)
To: gcc-bugs
It is beneficial to unroll reduction loop (and split the reduction target) to
reduce dependence height due to recurrence, but GCC does not perform such
optimization (-O3 -fno-tree-vectorize)
int a[1000];
int b[1000];
int foo(int n)
{
int s = 0;
int i = 0;
for (i = 0; i < 1000 ; i++)
{
s += a[i] + b[2*i];
}
return s;
}
--
Summary: Sum-reduction loop not recognized
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: xinliangli at gmail dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35343
^ permalink raw reply [flat|nested] 5+ messages in thread* [Bug middle-end/35343] Sum-reduction loop not recognized 2008-02-24 4:28 [Bug middle-end/35343] New: Sum-reduction loop not recognized xinliangli at gmail dot com @ 2008-02-24 21:56 ` rguenth at gcc dot gnu dot org 2008-02-25 10:22 ` dorit at gcc dot gnu dot org ` (2 subsequent siblings) 3 siblings, 0 replies; 5+ messages in thread From: rguenth at gcc dot gnu dot org @ 2008-02-24 21:56 UTC (permalink / raw) To: gcc-bugs -- rguenth at gcc dot gnu dot org changed: What |Removed |Added ---------------------------------------------------------------------------- Severity|normal |enhancement Keywords| |missed-optimization Version|unknown |4.3.0 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35343 ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/35343] Sum-reduction loop not recognized 2008-02-24 4:28 [Bug middle-end/35343] New: Sum-reduction loop not recognized xinliangli at gmail dot com 2008-02-24 21:56 ` [Bug middle-end/35343] " rguenth at gcc dot gnu dot org @ 2008-02-25 10:22 ` dorit at gcc dot gnu dot org 2008-02-25 21:37 ` xinliangli at gmail dot com 2008-12-29 6:32 ` [Bug middle-end/35343] Sum-reduction loop not recognized (enable -fvariable-expansion-in-unroller by default) pinskia at gcc dot gnu dot org 3 siblings, 0 replies; 5+ messages in thread From: dorit at gcc dot gnu dot org @ 2008-02-25 10:22 UTC (permalink / raw) To: gcc-bugs ------- Comment #1 from dorit at gcc dot gnu dot org 2008-02-25 10:21 ------- (In reply to comment #0) > It is beneficial to unroll reduction loop (and split the reduction target) to > reduce dependence height due to recurrence, but GCC does not perform such > optimization (-O3 -fno-tree-vectorize) it does, if you use -fvariable-expansion-in-unroller -funroll-loops (this splits the reduction target into 2 accumulators. For more agressive spiltting you can use --param max-variable-expansions-in-unrolle=[n]) -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35343 ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/35343] Sum-reduction loop not recognized 2008-02-24 4:28 [Bug middle-end/35343] New: Sum-reduction loop not recognized xinliangli at gmail dot com 2008-02-24 21:56 ` [Bug middle-end/35343] " rguenth at gcc dot gnu dot org 2008-02-25 10:22 ` dorit at gcc dot gnu dot org @ 2008-02-25 21:37 ` xinliangli at gmail dot com 2008-12-29 6:32 ` [Bug middle-end/35343] Sum-reduction loop not recognized (enable -fvariable-expansion-in-unroller by default) pinskia at gcc dot gnu dot org 3 siblings, 0 replies; 5+ messages in thread From: xinliangli at gmail dot com @ 2008-02-25 21:37 UTC (permalink / raw) To: gcc-bugs ------- Comment #2 from xinliangli at gmail dot com 2008-02-25 21:36 ------- (In reply to comment #1) > (In reply to comment #0) > > It is beneficial to unroll reduction loop (and split the reduction target) to > > reduce dependence height due to recurrence, but GCC does not perform such > > optimization (-O3 -fno-tree-vectorize) > > it does, if you use -fvariable-expansion-in-unroller -funroll-loops > (this splits the reduction target into 2 accumulators. For more agressive > spiltting you can use --param max-variable-expansions-in-unrolle=[n]) > Thanks, it is good to know the option. It would be good to tune the default behavior of the optimizer so that better out of box performance can be achieved. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35343 ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/35343] Sum-reduction loop not recognized (enable -fvariable-expansion-in-unroller by default) 2008-02-24 4:28 [Bug middle-end/35343] New: Sum-reduction loop not recognized xinliangli at gmail dot com ` (2 preceding siblings ...) 2008-02-25 21:37 ` xinliangli at gmail dot com @ 2008-12-29 6:32 ` pinskia at gcc dot gnu dot org 3 siblings, 0 replies; 5+ messages in thread From: pinskia at gcc dot gnu dot org @ 2008-12-29 6:32 UTC (permalink / raw) To: gcc-bugs ------- Comment #3 from pinskia at gcc dot gnu dot org 2008-12-29 06:30 ------- Confirmed. -- pinskia at gcc dot gnu dot org changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |NEW Ever Confirmed|0 |1 Last reconfirmed|0000-00-00 00:00:00 |2008-12-29 06:30:36 date| | Summary|Sum-reduction loop not |Sum-reduction loop not |recognized |recognized (enable - | |fvariable-expansion-in- | |unroller by default) http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35343 ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2008-12-29 6:32 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2008-02-24 4:28 [Bug middle-end/35343] New: Sum-reduction loop not recognized xinliangli at gmail dot com 2008-02-24 21:56 ` [Bug middle-end/35343] " rguenth at gcc dot gnu dot org 2008-02-25 10:22 ` dorit at gcc dot gnu dot org 2008-02-25 21:37 ` xinliangli at gmail dot com 2008-12-29 6:32 ` [Bug middle-end/35343] Sum-reduction loop not recognized (enable -fvariable-expansion-in-unroller by default) pinskia at gcc dot gnu dot org
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