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* [Bug tree-optimization/39300] New: vectorizer confused by predictive commoning
@ 2009-02-25 12:16 matz at gcc dot gnu dot org
2009-02-25 13:53 ` [Bug tree-optimization/39300] " matz at gcc dot gnu dot org
` (8 more replies)
0 siblings, 9 replies; 10+ messages in thread
From: matz at gcc dot gnu dot org @ 2009-02-25 12:16 UTC (permalink / raw)
To: gcc-bugs
The loop in this test is not vectorized if either PRE or predictive
commoning is active:
% cat vecttest2.f
subroutine Bench_StaggeredLeapfrog2( cctk_dim,XADM_curv_stag0,
&ADM_kzz_stag,lgxx,nx)
implicit none
INTEGER cctk_dim
INTEGER XADM_curv_stag0
REAL*8 ADM_kzz_stag(XADM_curv_stag0)
integer :: i
integer :: nx
REAL*8,DIMENSION(cctk_dim):: lgxx
do i=2,nx-1
ADM_kzz_stag(i) = ADM_kzz_stag(i)+lgxx(i)+lgxx(i-1)+lgxx(i+1)
end do
end subroutine Bench_StaggeredLeapfrog2
% gfortran -c -O3 -g -ffast-math -ftree-vectorizer-verbose=2 vecttest2.f
vecttest2.f:11: note: not vectorized: unsupported use in stmt.
vecttest2.f:12: note: not vectorized: unsupported use in stmt.
% add -fno-tree-pre -fno-predictive-commoning to above command:
vecttest2.f:11: note: LOOP VECTORIZED.
% add only -fno-tree-pre (so predictive commoning is active):
vecttest2.f:11: note: LOOP VECTORIZED.
vecttest2.f:12: note: not vectorized: unsupported use in stmt.
The one vectorized loop in case it mentions two of them is the tail loop
for the one produced by predictive commoning. That one doesn't contain
any loop carried values. Somehow the vectorizer doesn't like the
PHI nodes in the loop created by predictive commoning.
This testcase comes from 436.cactusADM, where it's very important to
vectorize a certain inner loop, and this (PRE and predcom) is one reason this
doesn't happen already.
--
Summary: vectorizer confused by predictive commoning
Product: gcc
Version: 4.4.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: matz at gcc dot gnu dot org
GCC host triplet: x86_64-linux
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39300
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/39300] vectorizer confused by predictive commoning
2009-02-25 12:16 [Bug tree-optimization/39300] New: vectorizer confused by predictive commoning matz at gcc dot gnu dot org
@ 2009-02-25 13:53 ` matz at gcc dot gnu dot org
2009-02-25 13:56 ` rguenth at gcc dot gnu dot org
` (7 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: matz at gcc dot gnu dot org @ 2009-02-25 13:53 UTC (permalink / raw)
To: gcc-bugs
------- Comment #1 from matz at gcc dot gnu dot org 2009-02-25 13:53 -------
For reference intel fortran (11.0) produces three loops, one where it uses
predictive commoning (that is used when there are only few iterations):
..B1.7: # Preds ..B1.6
movsd 8(%r8), %xmm1 #13.52
movsd (%r8), %xmm0 #13.52
# LOE rax rdx rcx rbx rbp rsi rdi r8 r9 r12 r13
r14 r15 xmm0 xmm1
..B1.8: # Preds ..B1.8 ..B1.7
movaps %xmm1, %xmm2 #13.33
movsd 16(%r8,%rdi,8), %xmm3 #13.52
addsd %xmm3, %xmm2 #13.33
addsd %xmm0, %xmm2 #13.41
movaps %xmm1, %xmm0 #14.7
movaps %xmm3, %xmm1 #14.7
addsd 8(%rdx,%rdi,8), %xmm2 #13.9
movsd %xmm2, 8(%rcx,%rdi,8) #13.9
incq %rdi #14.7
cmpq %rax, %rdi #14.7
jl ..B1.8 # Prob 82% #14.7
And two others which are vectorized (plus four/eight times unrolled), but
do _not_ use something like predictive commoning (i.e. no cross iteration
values). Both loops are just versions of each other, one for aligned
destinations and the other for unaligned. The aligned variant is this:
..B1.15: # Preds ..B1.10 ..B1.15
movsd 8(%rdx,%rax,8), %xmm1 #13.18
movhpd 16(%rdx,%rax,8), %xmm1 #13.18
movsd 8(%r8,%rax,8), %xmm0 #13.34
movhpd 16(%r8,%rax,8), %xmm0 #13.34
movsd 24(%rdx,%rax,8), %xmm4 #13.18
movhpd 32(%rdx,%rax,8), %xmm4 #13.18
movsd 24(%r8,%rax,8), %xmm2 #13.34
movhpd 32(%r8,%rax,8), %xmm2 #13.34
movsd 40(%rdx,%rax,8), %xmm7 #13.18
movhpd 48(%rdx,%rax,8), %xmm7 #13.18
movsd 40(%r8,%rax,8), %xmm5 #13.34
movhpd 48(%r8,%rax,8), %xmm5 #13.34
movsd 56(%rdx,%rax,8), %xmm10 #13.18
movhpd 64(%rdx,%rax,8), %xmm10 #13.18
movsd 56(%r8,%rax,8), %xmm8 #13.34
movhpd 64(%r8,%rax,8), %xmm8 #13.34
addpd %xmm0, %xmm1 #13.33
addpd (%r8,%rax,8), %xmm1 #13.41
addpd %xmm2, %xmm4 #13.33
addpd %xmm5, %xmm7 #13.33
addpd %xmm8, %xmm10 #13.33
movaps 16(%r8,%rax,8), %xmm3 #13.52
addpd %xmm3, %xmm1 #13.9
movaps 32(%r8,%rax,8), %xmm6 #13.52
movaps 48(%r8,%rax,8), %xmm9 #13.52
movaps %xmm1, 8(%rcx,%rax,8) #13.9
addpd %xmm3, %xmm4 #13.41
addpd %xmm6, %xmm4 #13.9
movaps %xmm4, 24(%rcx,%rax,8) #13.9
addpd %xmm6, %xmm7 #13.41
addpd %xmm9, %xmm7 #13.9
movaps %xmm7, 40(%rcx,%rax,8) #13.9
addpd %xmm9, %xmm10 #13.41
addpd 64(%r8,%rax,8), %xmm10 #13.9
movaps %xmm10, 56(%rcx,%rax,8) #13.9
addq $8, %rax #14.7
cmpq %r9, %rax #14.7
jl ..B1.15 # Prob 82% #14.7
Not most optimal, due to not using the cross-iteration values to save
two loads per iteration. But still much better than what GCC uses.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39300
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/39300] vectorizer confused by predictive commoning
2009-02-25 12:16 [Bug tree-optimization/39300] New: vectorizer confused by predictive commoning matz at gcc dot gnu dot org
2009-02-25 13:53 ` [Bug tree-optimization/39300] " matz at gcc dot gnu dot org
@ 2009-02-25 13:56 ` rguenth at gcc dot gnu dot org
2009-02-25 14:07 ` [Bug tree-optimization/39300] vectorizer confused by predictive commoning and PRE rguenth at gcc dot gnu dot org
` (6 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: rguenth at gcc dot gnu dot org @ 2009-02-25 13:56 UTC (permalink / raw)
To: gcc-bugs
------- Comment #2 from rguenth at gcc dot gnu dot org 2009-02-25 13:56 -------
Confirmed.
--
rguenth at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |rguenth at gcc dot gnu dot
| |org
Severity|normal |enhancement
Status|UNCONFIRMED |NEW
Ever Confirmed|0 |1
Keywords| |missed-optimization
Last reconfirmed|0000-00-00 00:00:00 |2009-02-25 13:56:08
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39300
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/39300] vectorizer confused by predictive commoning and PRE
2009-02-25 12:16 [Bug tree-optimization/39300] New: vectorizer confused by predictive commoning matz at gcc dot gnu dot org
2009-02-25 13:53 ` [Bug tree-optimization/39300] " matz at gcc dot gnu dot org
2009-02-25 13:56 ` rguenth at gcc dot gnu dot org
@ 2009-02-25 14:07 ` rguenth at gcc dot gnu dot org
2009-02-25 14:08 ` irar at il dot ibm dot com
` (5 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: rguenth at gcc dot gnu dot org @ 2009-02-25 14:07 UTC (permalink / raw)
To: gcc-bugs
------- Comment #3 from rguenth at gcc dot gnu dot org 2009-02-25 14:07 -------
Simpler C testcase:
float res[1024], data[1024];
void foo(void)
{
int i;
float tmp = data[0];
for (i = 1; i < 1024; ++i)
{
float tmp2 = data[i];
res[i] = tmp + tmp2;
tmp = tmp2;
}
}
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39300
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/39300] vectorizer confused by predictive commoning and PRE
2009-02-25 12:16 [Bug tree-optimization/39300] New: vectorizer confused by predictive commoning matz at gcc dot gnu dot org
` (2 preceding siblings ...)
2009-02-25 14:07 ` [Bug tree-optimization/39300] vectorizer confused by predictive commoning and PRE rguenth at gcc dot gnu dot org
@ 2009-02-25 14:08 ` irar at il dot ibm dot com
2009-03-08 14:26 ` dorit at gcc dot gnu dot org
` (4 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: irar at il dot ibm dot com @ 2009-02-25 14:08 UTC (permalink / raw)
To: gcc-bugs
------- Comment #4 from irar at il dot ibm dot com 2009-02-25 14:08 -------
Looks similar to PR 35229.
We get here:
# pre.1 = PHI <D.1, D.2>
..
load D.2
D.3 = D.2 + pre.1 + ...
store D.3
--
irar at il dot ibm dot com changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |irar at il dot ibm dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39300
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/39300] vectorizer confused by predictive commoning and PRE
2009-02-25 12:16 [Bug tree-optimization/39300] New: vectorizer confused by predictive commoning matz at gcc dot gnu dot org
` (3 preceding siblings ...)
2009-02-25 14:08 ` irar at il dot ibm dot com
@ 2009-03-08 14:26 ` dorit at gcc dot gnu dot org
2009-03-09 13:25 ` matz at gcc dot gnu dot org
` (3 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: dorit at gcc dot gnu dot org @ 2009-03-08 14:26 UTC (permalink / raw)
To: gcc-bugs
------- Comment #5 from dorit at gcc dot gnu dot org 2009-03-08 14:25 -------
This is a known problem... Indeed when Zdenek introduced predictive-commoning
there was a discussion on whether to schedule it before or after vectorization.
AFAIR, it ended up getting scheduled before the vectorizer just because this
happened to be what Zdenek tested/experimented with, and he didn't have a
problem with scheduling it after vectorization as long as it didn't hurt
performance (of mgrid in particular). Here are related threads:
http://gcc.gnu.org/ml/gcc-patches/2007-02/msg01383.html
http://gcc.gnu.org/ml/gcc-patches/2007-02/msg00555.html
http://gcc.gnu.org/ml/gcc-patches/2007-05/msg00571.html
Regardless of whether we scheudule predcom after vectorization, it will still
be useful to teach the vectorizer to handle such dependence patterns, as they
may (and do) appear in the source code.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39300
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/39300] vectorizer confused by predictive commoning and PRE
2009-02-25 12:16 [Bug tree-optimization/39300] New: vectorizer confused by predictive commoning matz at gcc dot gnu dot org
` (4 preceding siblings ...)
2009-03-08 14:26 ` dorit at gcc dot gnu dot org
@ 2009-03-09 13:25 ` matz at gcc dot gnu dot org
2009-07-22 15:31 ` matz at gcc dot gnu dot org
` (2 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: matz at gcc dot gnu dot org @ 2009-03-09 13:25 UTC (permalink / raw)
To: gcc-bugs
------- Comment #6 from matz at gcc dot gnu dot org 2009-03-09 13:25 -------
It's also PRE that produces such patterns, so moving predcom behind
vectorization alone won't help this problem.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39300
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/39300] vectorizer confused by predictive commoning and PRE
2009-02-25 12:16 [Bug tree-optimization/39300] New: vectorizer confused by predictive commoning matz at gcc dot gnu dot org
` (5 preceding siblings ...)
2009-03-09 13:25 ` matz at gcc dot gnu dot org
@ 2009-07-22 15:31 ` matz at gcc dot gnu dot org
2009-07-22 15:40 ` matz at gcc dot gnu dot org
2009-08-17 17:39 ` jessiecute13 at aol dot com
8 siblings, 0 replies; 10+ messages in thread
From: matz at gcc dot gnu dot org @ 2009-07-22 15:31 UTC (permalink / raw)
To: gcc-bugs
------- Comment #7 from matz at gcc dot gnu dot org 2009-07-22 15:31 -------
Subject: Bug 39300
Author: matz
Date: Wed Jul 22 15:30:50 2009
New Revision: 149942
URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=149942
Log:
PR tree-optimization/35229
PR tree-optimization/39300
* tree-ssa-pre.c (includes): Include tree-scalar-evolution.h.
(inhibit_phi_insertion): New function.
(insert_into_preds_of_block): Call it for REFERENCEs.
(init_pre): Initialize and finalize scalar evolutions.
* Makefile.in (tree-ssa-pre.o): Depend on tree-scalar-evolution.h .
testsuite/
* gcc.dg/vect/vect-pre-interact.c: New test.
Added:
trunk/gcc/testsuite/gcc.dg/vect/vect-pre-interact.c
Modified:
trunk/gcc/ChangeLog
trunk/gcc/testsuite/ChangeLog
trunk/gcc/tree-ssa-pre.c
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39300
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/39300] vectorizer confused by predictive commoning and PRE
2009-02-25 12:16 [Bug tree-optimization/39300] New: vectorizer confused by predictive commoning matz at gcc dot gnu dot org
` (6 preceding siblings ...)
2009-07-22 15:31 ` matz at gcc dot gnu dot org
@ 2009-07-22 15:40 ` matz at gcc dot gnu dot org
2009-08-17 17:39 ` jessiecute13 at aol dot com
8 siblings, 0 replies; 10+ messages in thread
From: matz at gcc dot gnu dot org @ 2009-07-22 15:40 UTC (permalink / raw)
To: gcc-bugs
------- Comment #8 from matz at gcc dot gnu dot org 2009-07-22 15:40 -------
So, the immediate problem is now fixed, but I'd suggest leaving this
enhancement request open, in case anybody wants to work on extending the
vectorizer to deal with these loop-carried dependencies, because in that
case we wouldn't need to dumb down PRE anymore, which would be even better.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39300
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug tree-optimization/39300] vectorizer confused by predictive commoning and PRE
2009-02-25 12:16 [Bug tree-optimization/39300] New: vectorizer confused by predictive commoning matz at gcc dot gnu dot org
` (7 preceding siblings ...)
2009-07-22 15:40 ` matz at gcc dot gnu dot org
@ 2009-08-17 17:39 ` jessiecute13 at aol dot com
8 siblings, 0 replies; 10+ messages in thread
From: jessiecute13 at aol dot com @ 2009-08-17 17:39 UTC (permalink / raw)
To: gcc-bugs
------- Comment #9 from jessiecute13 at aol dot com 2009-08-17 17:38 -------
$1.21
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39300
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2009-02-25 13:56 ` rguenth at gcc dot gnu dot org
2009-02-25 14:07 ` [Bug tree-optimization/39300] vectorizer confused by predictive commoning and PRE rguenth at gcc dot gnu dot org
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