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* [Bug c/52577] New: __builtin_shuffle -Wunused-but-set-* false positives
@ 2012-03-13 8:33 jakub at gcc dot gnu.org
2012-03-13 8:36 ` [Bug c/52577] " jakub at gcc dot gnu.org
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: jakub at gcc dot gnu.org @ 2012-03-13 8:33 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52577
Bug #: 52577
Summary: __builtin_shuffle -Wunused-but-set-* false positives
Classification: Unclassified
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: jakub@gcc.gnu.org
CC: marc.glisse@normalesup.org
Depends on: 52568
+++ This bug was initially created as a clone of Bug #52568 +++
Hello,
I compiled the following with -O3 (or -Os) and -mavx
#include <x86intrin.h>
__m256d left(__m256d x){
__m256i mask={1,2,3,0};
return __builtin_shuffle(x,mask);
}
(by the way, for some reason, gcc insists that 'mask' is set but not used with
-Wall)
and got:
vunpckhpd %xmm0, %xmm0, %xmm3
vmovapd %xmm0, %xmm1
vextractf128 $0x1, %ymm0, %xmm0
vmovaps %xmm0, %xmm2
vunpckhpd %xmm0, %xmm0, %xmm0
vunpcklpd %xmm1, %xmm0, %xmm1
vunpcklpd %xmm2, %xmm3, %xmm0
vinsertf128 $0x1, %xmm1, %ymm0, %ymm0
ret
That doesn't really match the code I currently use to do this:
#ifdef __AVX2__
__m256d d=_mm256_permute4x64_pd(x,1+2*4+3*16+0*64);
#else
__m256d b=_mm256_shuffle_pd(x,x,5);
__m256d c=_mm256_permute2f128_pd(b,b,1);
__m256d d=_mm256_blend_pd(b,c,10);
#endif
Could something recognizing this permutation pattern (and the right cyclic
shift) be added? I know there are too many shuffles to hand-code them all, but
cycles seem like they shouldn't be too uncommon.
With -mavx2, I get a single vpermq, which is close enough to the expected
vpermpd.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c/52577] __builtin_shuffle -Wunused-but-set-* false positives
2012-03-13 8:33 [Bug c/52577] New: __builtin_shuffle -Wunused-but-set-* false positives jakub at gcc dot gnu.org
@ 2012-03-13 8:36 ` jakub at gcc dot gnu.org
2012-03-13 8:59 ` jakub at gcc dot gnu.org
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: jakub at gcc dot gnu.org @ 2012-03-13 8:36 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52577
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |ASSIGNED
Last reconfirmed| |2012-03-13
AssignedTo|unassigned at gcc dot |jakub at gcc dot gnu.org
|gnu.org |
Target Milestone|--- |4.7.1
Ever Confirmed|0 |1
--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-03-13 08:35:58 UTC ---
Testcase for the false positive warnings:
/* PR c/52577 */
/* { dg-do compile } */
/* { dg-options "-Wall" } */
typedef int V __attribute__((vector_size (sizeof (int) * 4)));
void
f1 (V *p)
{
V mask = { 1, 2, 3, 0 };
*p = __builtin_shuffle (*p, mask);
}
void
f2 (V *p, V *q)
{
V mask = { 1, 2, 3, 0 };
*p = __builtin_shuffle (*p, *q, mask);
}
void
f3 (V *p, V *mask)
{
V a = { 1, 2, 3, 0 };
*p = __builtin_shuffle (a, *mask);
}
void
f4 (V *p, V *mask)
{
V a = { 1, 2, 3, 0 };
V b = { 2, 3, 4, 1 };
*p = __builtin_shuffle (a, b, *mask);
}
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c/52577] __builtin_shuffle -Wunused-but-set-* false positives
2012-03-13 8:33 [Bug c/52577] New: __builtin_shuffle -Wunused-but-set-* false positives jakub at gcc dot gnu.org
2012-03-13 8:36 ` [Bug c/52577] " jakub at gcc dot gnu.org
@ 2012-03-13 8:59 ` jakub at gcc dot gnu.org
2012-03-13 21:25 ` jakub at gcc dot gnu.org
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: jakub at gcc dot gnu.org @ 2012-03-13 8:59 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52577
--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-03-13 08:59:11 UTC ---
Created attachment 26884
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26884
gcc47-pr52577.patch
Untested fix.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c/52577] __builtin_shuffle -Wunused-but-set-* false positives
2012-03-13 8:33 [Bug c/52577] New: __builtin_shuffle -Wunused-but-set-* false positives jakub at gcc dot gnu.org
2012-03-13 8:36 ` [Bug c/52577] " jakub at gcc dot gnu.org
2012-03-13 8:59 ` jakub at gcc dot gnu.org
@ 2012-03-13 21:25 ` jakub at gcc dot gnu.org
2012-03-22 10:11 ` jakub at gcc dot gnu.org
2012-03-22 10:12 ` jakub at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: jakub at gcc dot gnu.org @ 2012-03-13 21:25 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52577
--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-03-13 21:19:56 UTC ---
Author: jakub
Date: Tue Mar 13 21:19:50 2012
New Revision: 185355
URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=185355
Log:
PR c/52577
* c-parser.c (c_parser_postfix_expression)
<case RID_BUILTIN_SHUFFLE>: Call mark_exp_read on argument values.
* gcc.dg/Wunused-var-3.c: New test.
Added:
trunk/gcc/testsuite/gcc.dg/Wunused-var-3.c
Modified:
trunk/gcc/ChangeLog
trunk/gcc/c-parser.c
trunk/gcc/testsuite/ChangeLog
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c/52577] __builtin_shuffle -Wunused-but-set-* false positives
2012-03-13 8:33 [Bug c/52577] New: __builtin_shuffle -Wunused-but-set-* false positives jakub at gcc dot gnu.org
` (2 preceding siblings ...)
2012-03-13 21:25 ` jakub at gcc dot gnu.org
@ 2012-03-22 10:11 ` jakub at gcc dot gnu.org
2012-03-22 10:12 ` jakub at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: jakub at gcc dot gnu.org @ 2012-03-22 10:11 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52577
--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-03-22 10:08:56 UTC ---
Author: jakub
Date: Thu Mar 22 10:08:49 2012
New Revision: 185682
URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=185682
Log:
Backported from mainline
2012-03-13 Jakub Jelinek <jakub@redhat.com>
PR c/52577
* c-parser.c (c_parser_postfix_expression)
<case RID_BUILTIN_SHUFFLE>: Call mark_exp_read on argument values.
* gcc.dg/Wunused-var-3.c: New test.
Added:
branches/gcc-4_7-branch/gcc/testsuite/gcc.dg/Wunused-var-3.c
Modified:
branches/gcc-4_7-branch/gcc/ChangeLog
branches/gcc-4_7-branch/gcc/c-parser.c
branches/gcc-4_7-branch/gcc/testsuite/ChangeLog
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c/52577] __builtin_shuffle -Wunused-but-set-* false positives
2012-03-13 8:33 [Bug c/52577] New: __builtin_shuffle -Wunused-but-set-* false positives jakub at gcc dot gnu.org
` (3 preceding siblings ...)
2012-03-22 10:11 ` jakub at gcc dot gnu.org
@ 2012-03-22 10:12 ` jakub at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: jakub at gcc dot gnu.org @ 2012-03-22 10:12 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52577
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|ASSIGNED |RESOLVED
Resolution| |FIXED
--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-03-22 10:11:21 UTC ---
Fixed.
^ permalink raw reply [flat|nested] 6+ messages in thread
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2012-03-13 8:33 [Bug c/52577] New: __builtin_shuffle -Wunused-but-set-* false positives jakub at gcc dot gnu.org
2012-03-13 8:36 ` [Bug c/52577] " jakub at gcc dot gnu.org
2012-03-13 8:59 ` jakub at gcc dot gnu.org
2012-03-13 21:25 ` jakub at gcc dot gnu.org
2012-03-22 10:11 ` jakub at gcc dot gnu.org
2012-03-22 10:12 ` jakub at gcc dot gnu.org
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