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* [Bug tree-optimization/112859] New: wrong code at -O3 on x86_64-linux-gnu
@ 2023-12-05 8:49 zhendong.su at inf dot ethz.ch
2023-12-05 13:18 ` [Bug tree-optimization/112859] [12/13/14 Regression] " rguenth at gcc dot gnu.org
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: zhendong.su at inf dot ethz.ch @ 2023-12-05 8:49 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112859
Bug ID: 112859
Summary: wrong code at -O3 on x86_64-linux-gnu
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: zhendong.su at inf dot ethz.ch
Target Milestone: ---
This appears to be a regression from 11.*, and affects 12.* and later.
Compiler Explorer: https://godbolt.org/z/aa8vrex9c
[555] % gcctk -v
Using built-in specs.
COLLECT_GCC=gcctk
COLLECT_LTO_WRAPPER=/local/home/suz/suz-local/software/local/gcc-trunk/bin/../libexec/gcc/x86_64-pc-linux-gnu/14.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-trunk/configure --disable-bootstrap
--enable-checking=yes --prefix=/local/suz-local/software/local/gcc-trunk
--enable-sanitizers --enable-languages=c,c++ --disable-werror --enable-multilib
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 14.0.0 20231205 (experimental) (GCC)
[556] %
[556] % gcctk -O2 small.c; ./a.out
[557] %
[557] % gcctk -O3 small.c
[558] % ./a.out
Aborted
[559] %
[559] % cat small.c
struct a {
char b;
int c;
} f, *i = &f;
static struct a e[4];
int *d, **g = &d;
static int h, j;
int main() {
for (; h < 1; h++) {
struct a k = {1, 1};
for (j = 0; j < 2; j++) {
*i = e[h];
e[h] = k;
}
*g = 0;
}
if (f.c != 1)
__builtin_abort();
return 0;
}
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/112859] [12/13/14 Regression] wrong code at -O3 on x86_64-linux-gnu
2023-12-05 8:49 [Bug tree-optimization/112859] New: wrong code at -O3 on x86_64-linux-gnu zhendong.su at inf dot ethz.ch
@ 2023-12-05 13:18 ` rguenth at gcc dot gnu.org
2023-12-05 13:53 ` rguenth at gcc dot gnu.org
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: rguenth at gcc dot gnu.org @ 2023-12-05 13:18 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112859
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target| |x86_64-*-*
Version|unknown |14.0
Keywords| |needs-bisection, wrong-code
Summary|wrong code at -O3 on |[12/13/14 Regression] wrong
|x86_64-linux-gnu |code at -O3 on
| |x86_64-linux-gnu
Target Milestone|--- |12.4
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/112859] [12/13/14 Regression] wrong code at -O3 on x86_64-linux-gnu
2023-12-05 8:49 [Bug tree-optimization/112859] New: wrong code at -O3 on x86_64-linux-gnu zhendong.su at inf dot ethz.ch
2023-12-05 13:18 ` [Bug tree-optimization/112859] [12/13/14 Regression] " rguenth at gcc dot gnu.org
@ 2023-12-05 13:53 ` rguenth at gcc dot gnu.org
2023-12-05 13:54 ` rguenth at gcc dot gnu.org
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: rguenth at gcc dot gnu.org @ 2023-12-05 13:53 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112859
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Assignee|unassigned at gcc dot gnu.org |rguenth at gcc dot gnu.org
See Also| |https://gcc.gnu.org/bugzill
| |a/show_bug.cgi?id=112281
Status|UNCONFIRMED |ASSIGNED
Last reconfirmed| |2023-12-05
Ever confirmed|0 |1
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
t.c:9:12: optimized: Loop nest 1 distributed: split to 2 loops and 0 library
calls.
-fno-tree-loop-distribution fixes this
GCC 11 distributes the inner loop, but only splits out the assignment to 'j'
there while with 12+ we distribute away the store to e[h].c. Looks somewhat
familiar to the other "aggregate copy" case where we have no evolution in
the inner loop.
The critical dependence is
(Data Dep:
#(Data Ref:
# bb: 5
# stmt: *i.1_1 = e[h.7_24];
# ref: e[h.7_24];
# base_object: e;
# Access function 0: {h.7_20, +, 1}_1
#)
#(Data Ref:
# bb: 5
# stmt: e[h.7_24].c = 1;
# ref: e[h.7_24].c;
# base_object: e;
# Access function 0: 32
# Access function 1: {h.7_20, +, 1}_1
#)
access_fn_A: {h.7_20, +, 1}_1
access_fn_B: {h.7_20, +, 1}_1
(subscript
iterations_that_access_an_element_twice_in_A: [0]
last_conflict: scev_not_known
iterations_that_access_an_element_twice_in_B: [0]
last_conflict: scev_not_known
(Subscript distance: 0 ))
loop nest: (1 2 )
distance_vector: 0 0
direction_vector: = =
)
which is then running into
/* If the overlap is exact preserve stmt order. */
else if (lambda_vector_zerop (DDR_DIST_VECT (ddr, 0),
DDR_NB_LOOPS (ddr)))
;
so maybe that special-casing is indeed incorrect, and the special-casing
I added
/* When then dependence distance of the innermost common
loop of the DRs is zero we have a conflict. */
auto l1 = gimple_bb (DR_STMT (dr1))->loop_father;
auto l2 = gimple_bb (DR_STMT (dr2))->loop_father;
int idx = index_in_loop_nest (find_common_loop (l1, l2)->num,
DDR_LOOP_NEST (ddr));
if (DDR_DIST_VECT (ddr, 0)[idx] == 0)
this_dir = 2;
should instead be handled to somehow handle more generally the situation that
two refs conflict in a loop where the refs do not evolve.
Thanks for these testcases btw.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/112859] [12/13/14 Regression] wrong code at -O3 on x86_64-linux-gnu
2023-12-05 8:49 [Bug tree-optimization/112859] New: wrong code at -O3 on x86_64-linux-gnu zhendong.su at inf dot ethz.ch
2023-12-05 13:18 ` [Bug tree-optimization/112859] [12/13/14 Regression] " rguenth at gcc dot gnu.org
2023-12-05 13:53 ` rguenth at gcc dot gnu.org
@ 2023-12-05 13:54 ` rguenth at gcc dot gnu.org
2023-12-05 19:14 ` zhendong.su at inf dot ethz.ch
2023-12-07 0:45 ` [Bug tree-optimization/112859] [12/13/14 Regression] wrong code at -O3 on x86_64-linux-gnu since r12-2097-g9f34b780b0461e sjames at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: rguenth at gcc dot gnu.org @ 2023-12-05 13:54 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112859
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Priority|P3 |P2
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/112859] [12/13/14 Regression] wrong code at -O3 on x86_64-linux-gnu
2023-12-05 8:49 [Bug tree-optimization/112859] New: wrong code at -O3 on x86_64-linux-gnu zhendong.su at inf dot ethz.ch
` (2 preceding siblings ...)
2023-12-05 13:54 ` rguenth at gcc dot gnu.org
@ 2023-12-05 19:14 ` zhendong.su at inf dot ethz.ch
2023-12-07 0:45 ` [Bug tree-optimization/112859] [12/13/14 Regression] wrong code at -O3 on x86_64-linux-gnu since r12-2097-g9f34b780b0461e sjames at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: zhendong.su at inf dot ethz.ch @ 2023-12-05 19:14 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112859
--- Comment #2 from Zhendong Su <zhendong.su at inf dot ethz.ch> ---
> Thanks for these testcases btw.
Happy to be of help, Richard.
And thanks to you folks for the incredible work and dedication!
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/112859] [12/13/14 Regression] wrong code at -O3 on x86_64-linux-gnu since r12-2097-g9f34b780b0461e
2023-12-05 8:49 [Bug tree-optimization/112859] New: wrong code at -O3 on x86_64-linux-gnu zhendong.su at inf dot ethz.ch
` (3 preceding siblings ...)
2023-12-05 19:14 ` zhendong.su at inf dot ethz.ch
@ 2023-12-07 0:45 ` sjames at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: sjames at gcc dot gnu.org @ 2023-12-07 0:45 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112859
Sam James <sjames at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords|needs-bisection |
CC| |sjames at gcc dot gnu.org
Summary|[12/13/14 Regression] wrong |[12/13/14 Regression] wrong
|code at -O3 on |code at -O3 on
|x86_64-linux-gnu |x86_64-linux-gnu since
| |r12-2097-g9f34b780b0461e
--- Comment #3 from Sam James <sjames at gcc dot gnu.org> ---
bisected to r12-2097-g9f34b780b0461e
^ permalink raw reply [flat|nested] 6+ messages in thread
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2023-12-05 8:49 [Bug tree-optimization/112859] New: wrong code at -O3 on x86_64-linux-gnu zhendong.su at inf dot ethz.ch
2023-12-05 13:18 ` [Bug tree-optimization/112859] [12/13/14 Regression] " rguenth at gcc dot gnu.org
2023-12-05 13:53 ` rguenth at gcc dot gnu.org
2023-12-05 13:54 ` rguenth at gcc dot gnu.org
2023-12-05 19:14 ` zhendong.su at inf dot ethz.ch
2023-12-07 0:45 ` [Bug tree-optimization/112859] [12/13/14 Regression] wrong code at -O3 on x86_64-linux-gnu since r12-2097-g9f34b780b0461e sjames at gcc dot gnu.org
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