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* [Bug tree-optimization/109893] New: [14 Regression] Missed Dead Code Elimination when using __builtin_unreachable since r14-160-gf828503eeb79ad1f1ada6db7deccc5abcc2f3ca3
@ 2023-05-17 15:15 theodort at inf dot ethz.ch
2023-05-17 15:29 ` [Bug tree-optimization/109893] " pinskia at gcc dot gnu.org
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: theodort at inf dot ethz.ch @ 2023-05-17 15:15 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109893
Bug ID: 109893
Summary: [14 Regression] Missed Dead Code Elimination when
using __builtin_unreachable since
r14-160-gf828503eeb79ad1f1ada6db7deccc5abcc2f3ca3
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: theodort at inf dot ethz.ch
Target Milestone: ---
void foo(void);
void bar(void);
static char a;
static int b, e, f;
static int *c = &b, *g;
int main() {
int *j = 0;
if (a) {
g = 0;
if (c)
bar();
} else {
j = &e;
c = 0;
}
if (c == &f == b || c == &e)
;
else
__builtin_unreachable();
if (g || e) {
if (j == &e || j == 0)
;
else
foo();
}
a = 4;
}
gcc -O3:
main:
cmpb $0, a(%rip)
je .L2
xorl %esi, %esi
cmpq $0, c(%rip)
movq %rsi, g(%rip)
je .L7
pushq %rdx
call bar
movb $4, a(%rip)
xorl %eax, %eax
popq %rcx
ret
.L2:
xorl %eax, %eax
movq %rax, c(%rip)
.L7:
movb $4, a(%rip)
xorl %eax, %eax
ret
c:
.quad b
gcc-trunk -O3
main:
subq $8, %rsp
cmpb $0, a(%rip)
je .L2
xorl %edx, %edx
cmpq $0, c(%rip)
movq %rdx, g(%rip)
je .L6
call bar
xorl %eax, %eax
.L4:
cmpq $0, g(%rip)
je .L9
.L6:
movb $4, a(%rip)
xorl %eax, %eax
addq $8, %rsp
ret
.L2:
xorl %eax, %eax
movq %rax, c(%rip)
movl $e, %eax
jmp .L4
.L9:
cmpl $0, e(%rip)
je .L6
testq %rax, %rax
je .L6
cmpq $e, %rax
je .L6
call foo
jmp .L6
c:
.quad b
Bisects to:
https://gcc.gnu.org/git/gitweb.cgi?p=gcc.git;h=f828503eeb79ad1f1ada6db7deccc5abcc2f3ca3
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/109893] [14 Regression] Missed Dead Code Elimination when using __builtin_unreachable since r14-160-gf828503eeb79ad1f1ada6db7deccc5abcc2f3ca3
2023-05-17 15:15 [Bug tree-optimization/109893] New: [14 Regression] Missed Dead Code Elimination when using __builtin_unreachable since r14-160-gf828503eeb79ad1f1ada6db7deccc5abcc2f3ca3 theodort at inf dot ethz.ch
@ 2023-05-17 15:29 ` pinskia at gcc dot gnu.org
2023-08-09 6:33 ` pinskia at gcc dot gnu.org
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-05-17 15:29 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109893
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
Keywords| |missed-optimization
Last reconfirmed| |2023-05-17
Status|UNCONFIRMED |NEW
Target Milestone|--- |14.0
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.
A minor regression I suspect.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/109893] [14 Regression] Missed Dead Code Elimination when using __builtin_unreachable since r14-160-gf828503eeb79ad1f1ada6db7deccc5abcc2f3ca3
2023-05-17 15:15 [Bug tree-optimization/109893] New: [14 Regression] Missed Dead Code Elimination when using __builtin_unreachable since r14-160-gf828503eeb79ad1f1ada6db7deccc5abcc2f3ca3 theodort at inf dot ethz.ch
2023-05-17 15:29 ` [Bug tree-optimization/109893] " pinskia at gcc dot gnu.org
@ 2023-08-09 6:33 ` pinskia at gcc dot gnu.org
2024-01-12 12:53 ` rguenth at gcc dot gnu.org
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-08-09 6:33 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109893
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
# j_10 = PHI <0B(4), &e(6)>
...
_21 = j_10 == 0B;
_22 = j_10 == &e;
_23 = _21 | _22;
The only pass which is able to optmize the above is pre.
That is take:
```
int e;
void g();
int f(int a, int b)
{
int *t;
if (a)
t = 0;
else
t = &e;
if (b)
g();
int t1 = t == 0;
int t2 = t == &e;
return t1|t2;
}
```
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/109893] [14 Regression] Missed Dead Code Elimination when using __builtin_unreachable since r14-160-gf828503eeb79ad1f1ada6db7deccc5abcc2f3ca3
2023-05-17 15:15 [Bug tree-optimization/109893] New: [14 Regression] Missed Dead Code Elimination when using __builtin_unreachable since r14-160-gf828503eeb79ad1f1ada6db7deccc5abcc2f3ca3 theodort at inf dot ethz.ch
2023-05-17 15:29 ` [Bug tree-optimization/109893] " pinskia at gcc dot gnu.org
2023-08-09 6:33 ` pinskia at gcc dot gnu.org
@ 2024-01-12 12:53 ` rguenth at gcc dot gnu.org
2024-03-08 15:36 ` law at gcc dot gnu.org
2024-05-07 7:40 ` [Bug tree-optimization/109893] [14/15 " rguenth at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: rguenth at gcc dot gnu.org @ 2024-01-12 12:53 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109893
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 #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
This is a failure to jump-thread because of size limits. If we'd limit
the backward threader the same way as the forward threader we'd optimize this
(--param fsm-scale-path-stmts=1).
--param max-jump-thread-duplication-stmts is 15
--param fsm-scale-path-stmts is 2
but for "true" FSM paths we allow --param max-fsm-thread-path-insns == 100
For non-loop FSM threads we only allow 7 stmts (and we lack the forward
thread estimation of the number of stmts we likely eliminate).
Increasing --param max-jump-thread-duplication-stmts to 17 also works to
resolve the regression.
But IMHO the scale param should simply go - we have the other limit for
paths across a backedge when threading multi-way branches. The argument
for the scaling is
/* The generic copier used by the backthreader does not re-use an
existing threading path to reduce code duplication. So for that
case, drastically reduce the number of statements we are allowed
to copy. */
that sounds more like limiting overall threading rather than individual
ones. I'll adjust fsm-scale-path-stmts to be more finely tunable.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/109893] [14 Regression] Missed Dead Code Elimination when using __builtin_unreachable since r14-160-gf828503eeb79ad1f1ada6db7deccc5abcc2f3ca3
2023-05-17 15:15 [Bug tree-optimization/109893] New: [14 Regression] Missed Dead Code Elimination when using __builtin_unreachable since r14-160-gf828503eeb79ad1f1ada6db7deccc5abcc2f3ca3 theodort at inf dot ethz.ch
` (2 preceding siblings ...)
2024-01-12 12:53 ` rguenth at gcc dot gnu.org
@ 2024-03-08 15:36 ` law at gcc dot gnu.org
2024-05-07 7:40 ` [Bug tree-optimization/109893] [14/15 " rguenth at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: law at gcc dot gnu.org @ 2024-03-08 15:36 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109893
Jeffrey A. Law <law at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Priority|P3 |P2
CC| |law at gcc dot gnu.org
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/109893] [14/15 Regression] Missed Dead Code Elimination when using __builtin_unreachable since r14-160-gf828503eeb79ad1f1ada6db7deccc5abcc2f3ca3
2023-05-17 15:15 [Bug tree-optimization/109893] New: [14 Regression] Missed Dead Code Elimination when using __builtin_unreachable since r14-160-gf828503eeb79ad1f1ada6db7deccc5abcc2f3ca3 theodort at inf dot ethz.ch
` (3 preceding siblings ...)
2024-03-08 15:36 ` law at gcc dot gnu.org
@ 2024-05-07 7:40 ` rguenth at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: rguenth at gcc dot gnu.org @ 2024-05-07 7:40 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109893
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|14.0 |14.2
--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 14.1 is being released, retargeting bugs to GCC 14.2.
^ permalink raw reply [flat|nested] 6+ messages in thread
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2023-05-17 15:15 [Bug tree-optimization/109893] New: [14 Regression] Missed Dead Code Elimination when using __builtin_unreachable since r14-160-gf828503eeb79ad1f1ada6db7deccc5abcc2f3ca3 theodort at inf dot ethz.ch
2023-05-17 15:29 ` [Bug tree-optimization/109893] " pinskia at gcc dot gnu.org
2023-08-09 6:33 ` pinskia at gcc dot gnu.org
2024-01-12 12:53 ` rguenth at gcc dot gnu.org
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