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* [Bug tree-optimization/50905] New: Gcc4.6.x's -ftree-parallelize-loops is effective only when using "-O2/-O3 -ffast-math"
@ 2011-10-28 19:37 xunxun1982 at gmail dot com
2011-10-28 19:45 ` [Bug tree-optimization/50905] " pinskia at gcc dot gnu.org
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: xunxun1982 at gmail dot com @ 2011-10-28 19:37 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50905
Bug #: 50905
Summary: Gcc4.6.x's -ftree-parallelize-loops is effective only
when using "-O2/-O3 -ffast-math"
Classification: Unclassified
Product: gcc
Version: 4.6.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: xunxun1982@gmail.com
Created attachment 25648
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=25648
the test
I found that Gcc4.6.1 and Gcc4.6.2 -ftree-parallelize-loops is effective only
when using "-O2/-O3 -ffast-math" on Windows or on Ubuntu.
Is this right?
Using my test,
$gcc -ftree-parallelize-loops=2 -c main.c
$nm main.o
U clock
0000000000000000 T main
U printf
U puts
U sin
$gcc -O2 -ftree-parallelize-loops=2 -c main.c
$nm main.o
0000000000000000 r .LC4
0000000000000008 r .LC6
U __printf_chk
U clock
0000000000000000 T main
U puts
U sin
$gcc -ffast-math -ftree-parallelize-loops=2 -c main.c
$nm main.o
U clock
0000000000000000 T main
U printf
U puts
U sin
$gcc -O2 -ftree-parallelize-loops=2 -ffast-math -c main.c
$nm main.o
0000000000000000 r .LC5
U GOMP_parallel_end
U GOMP_parallel_start
U __printf_chk
U clock
0000000000000000 T main
0000000000000000 t main._loopfn.0
U omp_get_num_threads
U omp_get_thread_num
U puts
U sin
Only -O2 -ftree-parallelize-loops=2 -ffast-math achieve my desired result.
But I think it should generate the similar symbols below when using
-ftree-parallelize-loops=2 alone:
U GOMP_parallel_end
U GOMP_parallel_start
U omp_get_num_threads
U omp_get_thread_num
Am I right?
Or the -ftree-parallelize-loops is such option that should be used with
"-O2/-O3 -ffast-math"?
Thanks.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/50905] Gcc4.6.x's -ftree-parallelize-loops is effective only when using "-O2/-O3 -ffast-math"
2011-10-28 19:37 [Bug tree-optimization/50905] New: Gcc4.6.x's -ftree-parallelize-loops is effective only when using "-O2/-O3 -ffast-math" xunxun1982 at gmail dot com
@ 2011-10-28 19:45 ` pinskia at gcc dot gnu.org
2011-10-28 19:54 ` xunxun1982 at gmail dot com
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu.org @ 2011-10-28 19:45 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50905
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution| |INVALID
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> 2011-10-28 19:45:18 UTC ---
>Am I right?
Yes but the reason comes down to fp math is not associative which means it is
impossible to do reductions with fp math unless you have -ffast-math (or really
-fassociative-math) turned on.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/50905] Gcc4.6.x's -ftree-parallelize-loops is effective only when using "-O2/-O3 -ffast-math"
2011-10-28 19:37 [Bug tree-optimization/50905] New: Gcc4.6.x's -ftree-parallelize-loops is effective only when using "-O2/-O3 -ffast-math" xunxun1982 at gmail dot com
2011-10-28 19:45 ` [Bug tree-optimization/50905] " pinskia at gcc dot gnu.org
@ 2011-10-28 19:54 ` xunxun1982 at gmail dot com
2011-10-28 20:07 ` pinskia at gcc dot gnu.org
2011-10-28 20:14 ` xunxun1982 at gmail dot com
3 siblings, 0 replies; 5+ messages in thread
From: xunxun1982 at gmail dot com @ 2011-10-28 19:54 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50905
xunxun <xunxun1982 at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|RESOLVED |UNCONFIRMED
Resolution|INVALID |
--- Comment #2 from xunxun <xunxun1982 at gmail dot com> 2011-10-28 19:53:47 UTC ---
(In reply to comment #1)
> >Am I right?
> Yes but the reason comes down to fp math is not associative which means it is
> impossible to do reductions with fp math unless you have -ffast-math (or really
> -fassociative-math) turned on.
But -ffast-math -ftree-parallelize-loops=2 is also no use.
We must combine -ffast-math and -O2/-O3.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/50905] Gcc4.6.x's -ftree-parallelize-loops is effective only when using "-O2/-O3 -ffast-math"
2011-10-28 19:37 [Bug tree-optimization/50905] New: Gcc4.6.x's -ftree-parallelize-loops is effective only when using "-O2/-O3 -ffast-math" xunxun1982 at gmail dot com
2011-10-28 19:45 ` [Bug tree-optimization/50905] " pinskia at gcc dot gnu.org
2011-10-28 19:54 ` xunxun1982 at gmail dot com
@ 2011-10-28 20:07 ` pinskia at gcc dot gnu.org
2011-10-28 20:14 ` xunxun1982 at gmail dot com
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu.org @ 2011-10-28 20:07 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50905
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution| |INVALID
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> 2011-10-28 20:07:03 UTC ---
Yes if you mean without -O1/-O2/-O3 -ftree-parallelize-loops does not work,
this is expected as explained in the manual, -O1 enables more than the options
that includes adding more optimizations.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/50905] Gcc4.6.x's -ftree-parallelize-loops is effective only when using "-O2/-O3 -ffast-math"
2011-10-28 19:37 [Bug tree-optimization/50905] New: Gcc4.6.x's -ftree-parallelize-loops is effective only when using "-O2/-O3 -ffast-math" xunxun1982 at gmail dot com
` (2 preceding siblings ...)
2011-10-28 20:07 ` pinskia at gcc dot gnu.org
@ 2011-10-28 20:14 ` xunxun1982 at gmail dot com
3 siblings, 0 replies; 5+ messages in thread
From: xunxun1982 at gmail dot com @ 2011-10-28 20:14 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50905
--- Comment #4 from xunxun <xunxun1982 at gmail dot com> 2011-10-28 20:14:38 UTC ---
(In reply to comment #3)
> Yes if you mean without -O1/-O2/-O3 -ftree-parallelize-loops does not work,
> this is expected as explained in the manual, -O1 enables more than the options
> that includes adding more optimizations.
Thanks for the information.
-----------------------
I read the manual:
-ftree-parallelize-loops=n
Parallelize loops, i.e., split their iteration space to run in n threads.
This is only possible for loops whose iterations are independent and can be
arbitrarily reordered. The optimization is only profitable on multiprocessor
machines, for loops that are CPU-intensive, rather than constrained e.g. by
memory bandwidth. This option implies -pthread, and thus is only supported on
targets that have support for -pthread.
I don't notice any -O1/-O2/-O3 Optimization information here.
-----------------------
If the information is true, we should only deal with the issue between
-ftree-parallelize-loops=n and -ffast-math
^ permalink raw reply [flat|nested] 5+ messages in thread
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2011-10-28 19:37 [Bug tree-optimization/50905] New: Gcc4.6.x's -ftree-parallelize-loops is effective only when using "-O2/-O3 -ffast-math" xunxun1982 at gmail dot com
2011-10-28 19:45 ` [Bug tree-optimization/50905] " pinskia at gcc dot gnu.org
2011-10-28 19:54 ` xunxun1982 at gmail dot com
2011-10-28 20:07 ` pinskia at gcc dot gnu.org
2011-10-28 20:14 ` xunxun1982 at gmail dot com
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