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* [Bug c/111137] New: Wrong code at -O2/3 since r12-1000-g6924b5e6bd3
@ 2023-08-24 15:47 shaohua.li at inf dot ethz.ch
2023-08-24 17:35 ` [Bug tree-optimization/111137] [12/13/14 Regression] " pinskia at gcc dot gnu.org
` (7 more replies)
0 siblings, 8 replies; 9+ messages in thread
From: shaohua.li at inf dot ethz.ch @ 2023-08-24 15:47 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111137
Bug ID: 111137
Summary: Wrong code at -O2/3 since r12-1000-g6924b5e6bd3
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: shaohua.li at inf dot ethz.ch
CC: rguenth at gcc dot gnu.org
Target Milestone: ---
gcc at -O2/3 produces the wrong code.
Bisected to r12-1000-g6924b5e6bd3
Compiler explorer: https://godbolt.org/z/9fo5dxxhf
$ cat a.c
int printf(const char *, ...);
char a;
int b[3][8];
int c, e = 1, f, g;
short d;
int main() {
for (; e >= 0; e--) {
d = 1;
for (; d >= 0; d--) {
c = 0;
for (; c <= 1; c++) {
b[0][d * 2 + c + 1] = 0;
g = a <= '7';
b[g - 1 + d][c] ^= 1;
}
}
}
printf("%d\n", b[0][1]);
}
$
$ gcc -O0 a.c && ./a.out
1
$ gcc -O2 a.c && ./a.out
0
$
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/111137] [12/13/14 Regression] Wrong code at -O2/3 since r12-1000-g6924b5e6bd3
2023-08-24 15:47 [Bug c/111137] New: Wrong code at -O2/3 since r12-1000-g6924b5e6bd3 shaohua.li at inf dot ethz.ch
@ 2023-08-24 17:35 ` pinskia at gcc dot gnu.org
2023-08-24 17:59 ` [Bug tree-optimization/111137] [11/12/13/14 Regression] Wrong code at -O2/3 pinskia at gcc dot gnu.org
` (6 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-08-24 17:35 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111137
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Summary|Wrong code at -O2/3 since |[12/13/14 Regression] Wrong
|r12-1000-g6924b5e6bd3 |code at -O2/3 since
| |r12-1000-g6924b5e6bd3
Target Milestone|--- |12.4
Component|c |tree-optimization
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/111137] [11/12/13/14 Regression] Wrong code at -O2/3
2023-08-24 15:47 [Bug c/111137] New: Wrong code at -O2/3 since r12-1000-g6924b5e6bd3 shaohua.li at inf dot ethz.ch
2023-08-24 17:35 ` [Bug tree-optimization/111137] [12/13/14 Regression] " pinskia at gcc dot gnu.org
@ 2023-08-24 17:59 ` pinskia at gcc dot gnu.org
2023-08-25 7:02 ` rguenth at gcc dot gnu.org
` (5 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-08-24 17:59 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111137
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
Known to fail| |11.1.0
Summary|[12/13/14 Regression] Wrong |[11/12/13/14 Regression]
|code at -O2/3 since |Wrong code at -O2/3
|r12-1000-g6924b5e6bd3 |
Known to work| |10.5.0
Last reconfirmed| |2023-08-24
Status|UNCONFIRMED |NEW
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Reduced a little further:
```
int b[3][8];
short d;
volatile int t = 1;
int main() {
int g = t;
for (int e = 1; e >= 0; e--) {
d = 1;
for (; d >= 0; d--) {
b[0][d * 2 + 1] = 0;
b[g - 1 + d][0] ^= 1;
b[0][d * 2 + 2] = 0;
b[g - 1 + d][1] ^= 1;
}
}
if (b[0][1] != 1)
__builtin_abort();
}
```
Note this fails with GCC 11.1.0 with `-O2 -ftree-vectorize` but passes with
`-O3` .
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/111137] [11/12/13/14 Regression] Wrong code at -O2/3
2023-08-24 15:47 [Bug c/111137] New: Wrong code at -O2/3 since r12-1000-g6924b5e6bd3 shaohua.li at inf dot ethz.ch
2023-08-24 17:35 ` [Bug tree-optimization/111137] [12/13/14 Regression] " pinskia at gcc dot gnu.org
2023-08-24 17:59 ` [Bug tree-optimization/111137] [11/12/13/14 Regression] Wrong code at -O2/3 pinskia at gcc dot gnu.org
@ 2023-08-25 7:02 ` rguenth at gcc dot gnu.org
2023-08-25 12:37 ` cvs-commit at gcc dot gnu.org
` (4 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: rguenth at gcc dot gnu.org @ 2023-08-25 7:02 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111137
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |ASSIGNED
Assignee|unassigned at gcc dot gnu.org |rguenth at gcc dot gnu.org
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
We BB vectorize as follows
<bb 3> [local count: 118111600]:
# ivtmp_29 = PHI <ivtmp_23(9), 2(2)>
- b[0][3] = 0;
_39 = g_21;
+ vectp.26_37 = &b[_39][0];
+ vect__15.27_4 = MEM <vector(2) int> [(int *)vectp.26_37];
+ vect__18.28_45 = vect__15.27_4 ^ { 1, 1 };
_15 = b[_39][0];
_18 = _15 ^ 1;
- b[_39][0] = _18;
- b[0][4] = 0;
_48 = b[_39][1];
_49 = _48 ^ 1;
- b[_39][1] = _49;
- b[0][1] = 0;
+ vectp.30_46 = &b[_39][0];
+ MEM <vector(2) int> [(int *)vectp.30_46] = vect__18.28_45;
_5 = _42;
+ vectp.20_36 = &b[_5][0];
+ vect__6.21_24 = MEM <vector(2) int> [(int *)vectp.20_36];
+ vect__7.22_35 = vect__6.21_24 ^ { 1, 1 };
_6 = b[_5][0];
_7 = _6 ^ 1;
- b[_5][0] = _7;
- b[0][2] = 0;
+ MEM <vector(4) int> [(int *)&b + 4B] = { 0, 0, 0, 0 };
_10 = b[_5][1];
_11 = _10 ^ 1;
- b[_5][1] = _11;
+ vectp.24_31 = &b[_5][0];
+ MEM <vector(2) int> [(int *)vectp.24_31] = vect__7.22_35;
ivtmp_23 = ivtmp_29 - 1;
if (ivtmp_23 != 0)
and the issue is that we somehow get data dependence wrong. _39 is 1 and
_5 is 0. That means we have
b[0][3] = 0;
_39 = g_21;
_15 = b[_39][0];
_18 = _15 ^ 1;
b[1 /*_39*/][0] = _18;
b[0][4] = 0;
_48 = b[_39][1];
_49 = _48 ^ 1;
b[1 /*_39*/][1] = _49;
b[0][1] = 0;
_5 = _42;
_6 = b[0 /*_5*/][0];
_7 = _6 ^ 1;
b[0 /*_5*/][0] = _7;
b[0][2] = 0;
_10 = b[0 /*_5*/][1];
_11 = _10 ^ 1;
b[0 /*_5*/][1] = _11;
I will have a look.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/111137] [11/12/13/14 Regression] Wrong code at -O2/3
2023-08-24 15:47 [Bug c/111137] New: Wrong code at -O2/3 since r12-1000-g6924b5e6bd3 shaohua.li at inf dot ethz.ch
` (2 preceding siblings ...)
2023-08-25 7:02 ` rguenth at gcc dot gnu.org
@ 2023-08-25 12:37 ` cvs-commit at gcc dot gnu.org
2023-08-25 12:54 ` [Bug tree-optimization/111137] [11/12/13 " rguenth at gcc dot gnu.org
` (3 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2023-08-25 12:37 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111137
--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Richard Biener <rguenth@gcc.gnu.org>:
https://gcc.gnu.org/g:845ee9c7107956845e487cb123fa581d9c70ea1b
commit r14-3480-g845ee9c7107956845e487cb123fa581d9c70ea1b
Author: Richard Biener <rguenther@suse.de>
Date: Fri Aug 25 13:37:30 2023 +0200
tree-optimization/111137 - dependence checking for SLP
The following fixes a mistake with SLP dependence checking. When
checking whether we can hoist loads to the first load place we
special-case stores of the same instance considering them sunk
to the last store place. But we fail to consider that stores from
other SLP instances are sunk in a similar way. This leads us to
miss the dependence between (A) and (B) in
b[0][1] = 0; (A)
...
_6 = b[_5 /* 0 */][0]; (B')
_7 = _6 ^ 1;
b[_5 /* 0 */][0] = _7;
b[0][2] = 0; (A')
_10 = b[_5 /* 0 */][1]; (B)
_11 = _10 ^ 1;
b[_5 /* 0 */][1] = _11;
where the zeroing stores are sunk to (A') and the loads hoisted
to (B'). The following fixes this, treating grouped stores from
other instances similar to stores from our own instance. The
difference is - and this is more conservative than necessary - that
we don't know which stores of a group are in which SLP instance
(though I believe either all of the grouped stores will be in
a single SLP instance or in none at the moment), so we don't
know which stores are sunk where. We simply assume they are
all sunk to the last store we run into. Likewise we do not take
into account that an SLP instance might be cancelled (or a grouped
store not actually belong to any instance).
PR tree-optimization/111137
* tree-vect-data-refs.cc (vect_slp_analyze_load_dependences):
Properly handle grouped stores from other SLP instances.
* gcc.dg/torture/pr111137.c: New testcase.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/111137] [11/12/13 Regression] Wrong code at -O2/3
2023-08-24 15:47 [Bug c/111137] New: Wrong code at -O2/3 since r12-1000-g6924b5e6bd3 shaohua.li at inf dot ethz.ch
` (3 preceding siblings ...)
2023-08-25 12:37 ` cvs-commit at gcc dot gnu.org
@ 2023-08-25 12:54 ` rguenth at gcc dot gnu.org
2023-11-24 15:13 ` cvs-commit at gcc dot gnu.org
` (2 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: rguenth at gcc dot gnu.org @ 2023-08-25 12:54 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111137
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Known to work| |14.0
Summary|[11/12/13/14 Regression] |[11/12/13 Regression] Wrong
|Wrong code at -O2/3 |code at -O2/3
--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed on trunk sofar.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/111137] [11/12/13 Regression] Wrong code at -O2/3
2023-08-24 15:47 [Bug c/111137] New: Wrong code at -O2/3 since r12-1000-g6924b5e6bd3 shaohua.li at inf dot ethz.ch
` (4 preceding siblings ...)
2023-08-25 12:54 ` [Bug tree-optimization/111137] [11/12/13 " rguenth at gcc dot gnu.org
@ 2023-11-24 15:13 ` cvs-commit at gcc dot gnu.org
2023-11-24 15:14 ` [Bug tree-optimization/111137] [11/12 " rguenth at gcc dot gnu.org
2023-12-15 13:17 ` [Bug tree-optimization/111137] [11/12 Regression] Wrong code at -O2/3 since r12-1000-g6924b5e6bd3 cvs-commit at gcc dot gnu.org
7 siblings, 0 replies; 9+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2023-11-24 15:13 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111137
--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-13 branch has been updated by Richard Biener
<rguenth@gcc.gnu.org>:
https://gcc.gnu.org/g:4649121c8e3bae1315e265ad2e205990e39573c5
commit r13-8095-g4649121c8e3bae1315e265ad2e205990e39573c5
Author: Richard Biener <rguenther@suse.de>
Date: Fri Aug 25 13:37:30 2023 +0200
tree-optimization/111137 - dependence checking for SLP
The following fixes a mistake with SLP dependence checking. When
checking whether we can hoist loads to the first load place we
special-case stores of the same instance considering them sunk
to the last store place. But we fail to consider that stores from
other SLP instances are sunk in a similar way. This leads us to
miss the dependence between (A) and (B) in
b[0][1] = 0; (A)
...
_6 = b[_5 /* 0 */][0]; (B')
_7 = _6 ^ 1;
b[_5 /* 0 */][0] = _7;
b[0][2] = 0; (A')
_10 = b[_5 /* 0 */][1]; (B)
_11 = _10 ^ 1;
b[_5 /* 0 */][1] = _11;
where the zeroing stores are sunk to (A') and the loads hoisted
to (B'). The following fixes this, treating grouped stores from
other instances similar to stores from our own instance. The
difference is - and this is more conservative than necessary - that
we don't know which stores of a group are in which SLP instance
(though I believe either all of the grouped stores will be in
a single SLP instance or in none at the moment), so we don't
know which stores are sunk where. We simply assume they are
all sunk to the last store we run into. Likewise we do not take
into account that an SLP instance might be cancelled (or a grouped
store not actually belong to any instance).
PR tree-optimization/111137
* tree-vect-data-refs.cc (vect_slp_analyze_load_dependences):
Properly handle grouped stores from other SLP instances.
* gcc.dg/torture/pr111137.c: New testcase.
(cherry picked from commit 845ee9c7107956845e487cb123fa581d9c70ea1b)
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/111137] [11/12 Regression] Wrong code at -O2/3
2023-08-24 15:47 [Bug c/111137] New: Wrong code at -O2/3 since r12-1000-g6924b5e6bd3 shaohua.li at inf dot ethz.ch
` (5 preceding siblings ...)
2023-11-24 15:13 ` cvs-commit at gcc dot gnu.org
@ 2023-11-24 15:14 ` rguenth at gcc dot gnu.org
2023-12-15 13:17 ` [Bug tree-optimization/111137] [11/12 Regression] Wrong code at -O2/3 since r12-1000-g6924b5e6bd3 cvs-commit at gcc dot gnu.org
7 siblings, 0 replies; 9+ messages in thread
From: rguenth at gcc dot gnu.org @ 2023-11-24 15:14 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111137
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Known to fail| |13.2.0
Known to work| |13.2.1
Priority|P3 |P2
Summary|[11/12/13 Regression] Wrong |[11/12 Regression] Wrong
|code at -O2/3 |code at -O2/3
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/111137] [11/12 Regression] Wrong code at -O2/3 since r12-1000-g6924b5e6bd3
2023-08-24 15:47 [Bug c/111137] New: Wrong code at -O2/3 since r12-1000-g6924b5e6bd3 shaohua.li at inf dot ethz.ch
` (6 preceding siblings ...)
2023-11-24 15:14 ` [Bug tree-optimization/111137] [11/12 " rguenth at gcc dot gnu.org
@ 2023-12-15 13:17 ` cvs-commit at gcc dot gnu.org
7 siblings, 0 replies; 9+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2023-12-15 13:17 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111137
--- Comment #6 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-12 branch has been updated by Richard Biener
<rguenth@gcc.gnu.org>:
https://gcc.gnu.org/g:e35556c61bdeb9f41b4111fffb423a705232ab9c
commit r12-10043-ge35556c61bdeb9f41b4111fffb423a705232ab9c
Author: Richard Biener <rguenther@suse.de>
Date: Fri Aug 25 13:37:30 2023 +0200
tree-optimization/111137 - dependence checking for SLP
The following fixes a mistake with SLP dependence checking. When
checking whether we can hoist loads to the first load place we
special-case stores of the same instance considering them sunk
to the last store place. But we fail to consider that stores from
other SLP instances are sunk in a similar way. This leads us to
miss the dependence between (A) and (B) in
b[0][1] = 0; (A)
...
_6 = b[_5 /* 0 */][0]; (B')
_7 = _6 ^ 1;
b[_5 /* 0 */][0] = _7;
b[0][2] = 0; (A')
_10 = b[_5 /* 0 */][1]; (B)
_11 = _10 ^ 1;
b[_5 /* 0 */][1] = _11;
where the zeroing stores are sunk to (A') and the loads hoisted
to (B'). The following fixes this, treating grouped stores from
other instances similar to stores from our own instance. The
difference is - and this is more conservative than necessary - that
we don't know which stores of a group are in which SLP instance
(though I believe either all of the grouped stores will be in
a single SLP instance or in none at the moment), so we don't
know which stores are sunk where. We simply assume they are
all sunk to the last store we run into. Likewise we do not take
into account that an SLP instance might be cancelled (or a grouped
store not actually belong to any instance).
PR tree-optimization/111137
* tree-vect-data-refs.cc (vect_slp_analyze_load_dependences):
Properly handle grouped stores from other SLP instances.
* gcc.dg/torture/pr111137.c: New testcase.
(cherry picked from commit 845ee9c7107956845e487cb123fa581d9c70ea1b)
^ permalink raw reply [flat|nested] 9+ messages in thread
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2023-08-24 17:35 ` [Bug tree-optimization/111137] [12/13/14 Regression] " pinskia at gcc dot gnu.org
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