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* [Bug tree-optimization/56624] New: Vectorizer gives up on a group-access if it contains stores to the same location
@ 2013-03-15 11:51 michael.v.zolotukhin at gmail dot com
2013-03-15 11:55 ` [Bug tree-optimization/56624] " rguenth at gcc dot gnu.org
` (7 more replies)
0 siblings, 8 replies; 9+ messages in thread
From: michael.v.zolotukhin at gmail dot com @ 2013-03-15 11:51 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56624
Bug #: 56624
Summary: Vectorizer gives up on a group-access if it contains
stores to the same location
Classification: Unclassified
Product: gcc
Version: 4.8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: michael.v.zolotukhin@gmail.com
Build: 4.8.0 20130313
Created attachment 29672
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29672
Reproducer
GCC can't vectorize such loop:
void foo (double *a)
{
int i;
for (i = 0; i < 100; i+=2)
{
a[i+1] = 2;
a[i] = 3;
a[i+1] = 2;
a[i] = 3;
}
}
Vectorizer reports following:
note: === vect_analyze_data_ref_accesses ===
note: Detected interleaving of size 2
note: Two store stmts share the same dr.
note: not vectorized: complicated access pattern.
Obviously, in this given case vectorization is possible because the first
stores have no effect.
This test is a reproducer of similar problem encountered on Spec2006/470.lbm -
there if-conversion could produce stores to the same location which will stop
vectorizer.
The test is attached, command line to reproduce:
gcc group_access.c -O3 -c -ftree-vectorizer-verbose=15
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/56624] Vectorizer gives up on a group-access if it contains stores to the same location
2013-03-15 11:51 [Bug tree-optimization/56624] New: Vectorizer gives up on a group-access if it contains stores to the same location michael.v.zolotukhin at gmail dot com
@ 2013-03-15 11:55 ` rguenth at gcc dot gnu.org
2013-03-15 12:20 ` michael.v.zolotukhin at gmail dot com
` (6 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: rguenth at gcc dot gnu.org @ 2013-03-15 11:55 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56624
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |WAITING
Last reconfirmed| |2013-03-15
Ever Confirmed|0 |1
Known to fail| |4.8.0
Build|4.8.0 20130313 |
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> 2013-03-15 11:54:50 UTC ---
> This test is a reproducer of similar problem encountered on Spec2006/470.lbm -
> there if-conversion could produce stores to the same location which will stop
> vectorizer.
Can you reproduce a testcase for that instead? It doesn't make sense
to handle code that should be optimized earlier (by DSE). Is it from
code like
if (cond)
a[i] = 3;
else
a[i] = 3;
?
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/56624] Vectorizer gives up on a group-access if it contains stores to the same location
2013-03-15 11:51 [Bug tree-optimization/56624] New: Vectorizer gives up on a group-access if it contains stores to the same location michael.v.zolotukhin at gmail dot com
2013-03-15 11:55 ` [Bug tree-optimization/56624] " rguenth at gcc dot gnu.org
@ 2013-03-15 12:20 ` michael.v.zolotukhin at gmail dot com
2013-03-15 12:27 ` michael.v.zolotukhin at gmail dot com
` (5 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: michael.v.zolotukhin at gmail dot com @ 2013-03-15 12:20 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56624
--- Comment #2 from Michael Zolotukhin <michael.v.zolotukhin at gmail dot com> 2013-03-15 12:19:50 UTC ---
> Can you reproduce a testcase for that instead? It doesn't make sense
> to handle code that should be optimized earlier (by DSE). Is it from
> code like
>
> if (cond)
> a[i] = 3;
> else
> a[i] = 3;
>
> ?
Yes, originally it is from the code similar to your example, but this example
has one more problem which hides the one described in this tracker. I've
submitted one more bug with the test almost like yours (56625).
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/56624] Vectorizer gives up on a group-access if it contains stores to the same location
2013-03-15 11:51 [Bug tree-optimization/56624] New: Vectorizer gives up on a group-access if it contains stores to the same location michael.v.zolotukhin at gmail dot com
2013-03-15 11:55 ` [Bug tree-optimization/56624] " rguenth at gcc dot gnu.org
2013-03-15 12:20 ` michael.v.zolotukhin at gmail dot com
@ 2013-03-15 12:27 ` michael.v.zolotukhin at gmail dot com
2013-03-15 12:28 ` michael.v.zolotukhin at gmail dot com
` (4 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: michael.v.zolotukhin at gmail dot com @ 2013-03-15 12:27 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56624
--- Comment #3 from Michael Zolotukhin <michael.v.zolotukhin at gmail dot com> 2013-03-15 12:26:46 UTC ---
Created attachment 29674
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29674
Reproducer 2
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/56624] Vectorizer gives up on a group-access if it contains stores to the same location
2013-03-15 11:51 [Bug tree-optimization/56624] New: Vectorizer gives up on a group-access if it contains stores to the same location michael.v.zolotukhin at gmail dot com
` (2 preceding siblings ...)
2013-03-15 12:27 ` michael.v.zolotukhin at gmail dot com
@ 2013-03-15 12:28 ` michael.v.zolotukhin at gmail dot com
2013-03-15 12:32 ` rguenth at gcc dot gnu.org
` (3 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: michael.v.zolotukhin at gmail dot com @ 2013-03-15 12:28 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56624
--- Comment #4 from Michael Zolotukhin <michael.v.zolotukhin at gmail dot com> 2013-03-15 12:27:51 UTC ---
Sorry, it looks like the reproducer with if could be made, and here it is:
void foo (long *a)
{
int i;
for (i = 0; i < 100; i+=2)
{
if (a[i] == 0)
{
a[i+1] = 2;
a[i] = 3;
}
else
{
a[i+1] = 3;
a[i] = 4;
}
}
}
In this example we have:
group_access2.c:4: note: === vect_analyze_data_ref_accesses ===
group_access2.c:4: note: READ_WRITE dependence in interleaving.
group_access2.c:4: note: not vectorized: complicated access pattern.
group_access2.c:4: note: bad data access.
group_access2.c:1: note: vectorized 0 loops in function.
The diagnostic is a bit different, but rootcause is the same I guess.
The test is attached (reproducer 2).
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/56624] Vectorizer gives up on a group-access if it contains stores to the same location
2013-03-15 11:51 [Bug tree-optimization/56624] New: Vectorizer gives up on a group-access if it contains stores to the same location michael.v.zolotukhin at gmail dot com
` (3 preceding siblings ...)
2013-03-15 12:28 ` michael.v.zolotukhin at gmail dot com
@ 2013-03-15 12:32 ` rguenth at gcc dot gnu.org
2020-09-14 12:44 ` rguenth at gcc dot gnu.org
` (2 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: rguenth at gcc dot gnu.org @ 2013-03-15 12:32 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56624
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|WAITING |NEW
Blocks| |53947
--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> 2013-03-15 12:31:57 UTC ---
Thanks and confirmed.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/56624] Vectorizer gives up on a group-access if it contains stores to the same location
2013-03-15 11:51 [Bug tree-optimization/56624] New: Vectorizer gives up on a group-access if it contains stores to the same location michael.v.zolotukhin at gmail dot com
` (4 preceding siblings ...)
2013-03-15 12:32 ` rguenth at gcc dot gnu.org
@ 2020-09-14 12:44 ` rguenth at gcc dot gnu.org
2024-03-10 5:22 ` pinskia at gcc dot gnu.org
2024-03-10 5:25 ` pinskia at gcc dot gnu.org
7 siblings, 0 replies; 9+ messages in thread
From: rguenth at gcc dot gnu.org @ 2020-09-14 12:44 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56624
--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Michael Zolotukhin from comment #4)
> Sorry, it looks like the reproducer with if could be made, and here it is:
> void foo (long *a)
> {
> int i;
> for (i = 0; i < 100; i+=2)
> {
> if (a[i] == 0)
> {
> a[i+1] = 2;
> a[i] = 3;
> }
> else
> {
> a[i+1] = 3;
> a[i] = 4;
> }
> }
> }
> In this example we have:
> group_access2.c:4: note: === vect_analyze_data_ref_accesses ===
> group_access2.c:4: note: READ_WRITE dependence in interleaving.
> group_access2.c:4: note: not vectorized: complicated access pattern.
> group_access2.c:4: note: bad data access.
> group_access2.c:1: note: vectorized 0 loops in function.
>
> The diagnostic is a bit different, but rootcause is the same I guess.
>
> The test is attached (reproducer 2).
We now vectorize this loop (not with plain SSE2 but with SSE4.2 for example):
.L2:
movq (%rdi), %xmm0
movdqa %xmm2, %xmm4
addq $16, %rdi
punpcklqdq %xmm0, %xmm0
pcmpeqq %xmm1, %xmm0
pblendvb %xmm0, %xmm3, %xmm4
movups %xmm4, -16(%rdi)
cmpq %rdi, %rax
jne .L2
probably because we now sink the common stores from the if arm. Modifying
the testcase to the following reproduces the original issue again:
void foo (long *a)
{
int i;
for (i = 0; i < 100; i+=2)
{
if (a[i] == 0)
{
a[i+1] = 2;
a[i] = 3;
}
else
{
a[i] = 4;
a[i+1] = 3;
}
}
}
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/56624] Vectorizer gives up on a group-access if it contains stores to the same location
2013-03-15 11:51 [Bug tree-optimization/56624] New: Vectorizer gives up on a group-access if it contains stores to the same location michael.v.zolotukhin at gmail dot com
` (5 preceding siblings ...)
2020-09-14 12:44 ` rguenth at gcc dot gnu.org
@ 2024-03-10 5:22 ` pinskia at gcc dot gnu.org
2024-03-10 5:25 ` pinskia at gcc dot gnu.org
7 siblings, 0 replies; 9+ messages in thread
From: pinskia at gcc dot gnu.org @ 2024-03-10 5:22 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56624
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Known to work| |9.1.0
--- Comment #7 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Looks like all of the testcases vectorize since GCC 11 as far as I can tell.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/56624] Vectorizer gives up on a group-access if it contains stores to the same location
2013-03-15 11:51 [Bug tree-optimization/56624] New: Vectorizer gives up on a group-access if it contains stores to the same location michael.v.zolotukhin at gmail dot com
` (6 preceding siblings ...)
2024-03-10 5:22 ` pinskia at gcc dot gnu.org
@ 2024-03-10 5:25 ` pinskia at gcc dot gnu.org
7 siblings, 0 replies; 9+ messages in thread
From: pinskia at gcc dot gnu.org @ 2024-03-10 5:25 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56624
--- Comment #8 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
For aarch64, it has been since GCC 13 though for the testcase in comment #6 .
^ permalink raw reply [flat|nested] 9+ messages in thread
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2013-03-15 11:51 [Bug tree-optimization/56624] New: Vectorizer gives up on a group-access if it contains stores to the same location michael.v.zolotukhin at gmail dot com
2013-03-15 11:55 ` [Bug tree-optimization/56624] " rguenth at gcc dot gnu.org
2013-03-15 12:20 ` michael.v.zolotukhin at gmail dot com
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