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* [Bug rtl-optimization/110791] New: [12/13/14 Regression] arm: Wrong code with -Os -march=armv8.1-m.main
@ 2023-07-24 10:51 acoplan at gcc dot gnu.org
2023-07-24 11:24 ` [Bug rtl-optimization/110791] " xry111 at gcc dot gnu.org
` (8 more replies)
0 siblings, 9 replies; 10+ messages in thread
From: acoplan at gcc dot gnu.org @ 2023-07-24 10:51 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110791
Bug ID: 110791
Summary: [12/13/14 Regression] arm: Wrong code with -Os
-march=armv8.1-m.main
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: acoplan at gcc dot gnu.org
Target Milestone: ---
The following testcase is miscompiled since at least GCC 12 with -Os
-march=armv8.1-m.main:
void __attribute__ ((noinline))
foo (char *path, int *result)
{
char *p = path;
while (p >= path && *p != '/')
p--;
while (p > path && p[-1] == '/')
p--;
if (p < path)
*result = 1;
}
int main(void)
{
char path[4] = "usr";
int x = 0;
foo (path + 2, &x);
if (!x)
__builtin_abort ();
}
Below is the assembly we currently generate together with comments showing how
this goes wrong at runtime:
foo:
mov r3, r0 @ r3 <- (p = path)
ldrb r2, [r3], #-1 @ r2 <- *p; p--;
cmp r2, #47
it eq
moveq r3, r0 @ if (r2 == 47) p <- path
subs r2, r3, r0
cmp r0, r3
add r2, r2, #1
bhi .L9 @ if (path > p) goto .L9 [taken]
adds r0, r0, #1
bne .L6
.L9:
movs r2, #1
.L6:
subs r2, r2, #1 @ r2 <- 0 [fall through from above]
bne .L3 @ [not taken, r2 was #1]
bcc .L4 @ [not taken]
bx lr @ [return without setting *result = 1]
.L3:
ldrb r0, [r3, #-1]!
cmp r0, #47
beq .L6
bx lr
.L4:
movs r3, #1
str r3, [r1]
bx lr
At -O2 the code is both correct and much better quality:
foo:
ldrb r3, [r0] @ zero_extendqisi2
cmp r3, #47
itt ne
movne r3, #1
strne r3, [r1]
bx lr
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug rtl-optimization/110791] [12/13/14 Regression] arm: Wrong code with -Os -march=armv8.1-m.main
2023-07-24 10:51 [Bug rtl-optimization/110791] New: [12/13/14 Regression] arm: Wrong code with -Os -march=armv8.1-m.main acoplan at gcc dot gnu.org
@ 2023-07-24 11:24 ` xry111 at gcc dot gnu.org
2023-07-24 11:27 ` acoplan at gcc dot gnu.org
` (7 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: xry111 at gcc dot gnu.org @ 2023-07-24 11:24 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110791
Xi Ruoyao <xry111 at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |WAITING
CC| |xry111 at gcc dot gnu.org
Ever confirmed|0 |1
Last reconfirmed| |2023-07-24
--- Comment #1 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
Isn't this a UB?
while (p >= path && *p != '/')
p--;
This will cause p to become "&main::path[0] - 1". C23 6.5.6p9:
If the pointer operand and the result do not point to elements of the same
array object or one past the last element of the array object, the behavior is
undefined.
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug rtl-optimization/110791] [12/13/14 Regression] arm: Wrong code with -Os -march=armv8.1-m.main
2023-07-24 10:51 [Bug rtl-optimization/110791] New: [12/13/14 Regression] arm: Wrong code with -Os -march=armv8.1-m.main acoplan at gcc dot gnu.org
2023-07-24 11:24 ` [Bug rtl-optimization/110791] " xry111 at gcc dot gnu.org
@ 2023-07-24 11:27 ` acoplan at gcc dot gnu.org
2023-07-24 11:29 ` xry111 at gcc dot gnu.org
` (6 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: acoplan at gcc dot gnu.org @ 2023-07-24 11:27 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110791
--- Comment #2 from Alex Coplan <acoplan at gcc dot gnu.org> ---
(In reply to Xi Ruoyao from comment #1)
> Isn't this a UB?
>
> while (p >= path && *p != '/')
> p--;
>
> This will cause p to become "&main::path[0] - 1". C23 6.5.6p9:
In this case, with the input given in main, I think p should end up pointing to
main::path + 1 (since we pass in main::path + 2, and foo can only ever
decrement p at most one below its parameter path).
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug rtl-optimization/110791] [12/13/14 Regression] arm: Wrong code with -Os -march=armv8.1-m.main
2023-07-24 10:51 [Bug rtl-optimization/110791] New: [12/13/14 Regression] arm: Wrong code with -Os -march=armv8.1-m.main acoplan at gcc dot gnu.org
2023-07-24 11:24 ` [Bug rtl-optimization/110791] " xry111 at gcc dot gnu.org
2023-07-24 11:27 ` acoplan at gcc dot gnu.org
@ 2023-07-24 11:29 ` xry111 at gcc dot gnu.org
2023-07-24 13:09 ` wilco at gcc dot gnu.org
` (5 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: xry111 at gcc dot gnu.org @ 2023-07-24 11:29 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110791
Xi Ruoyao <xry111 at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|WAITING |UNCONFIRMED
Ever confirmed|1 |0
--- Comment #3 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
(In reply to Alex Coplan from comment #2)
> (In reply to Xi Ruoyao from comment #1)
> > Isn't this a UB?
> >
> > while (p >= path && *p != '/')
> > p--;
> >
> > This will cause p to become "&main::path[0] - 1". C23 6.5.6p9:
>
> In this case, with the input given in main, I think p should end up pointing
> to main::path + 1 (since we pass in main::path + 2, and foo can only ever
> decrement p at most one below its parameter path).
Sorry, I misread the code. I guess I need to drink some coffee now...
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug rtl-optimization/110791] [12/13/14 Regression] arm: Wrong code with -Os -march=armv8.1-m.main
2023-07-24 10:51 [Bug rtl-optimization/110791] New: [12/13/14 Regression] arm: Wrong code with -Os -march=armv8.1-m.main acoplan at gcc dot gnu.org
` (2 preceding siblings ...)
2023-07-24 11:29 ` xry111 at gcc dot gnu.org
@ 2023-07-24 13:09 ` wilco at gcc dot gnu.org
2023-07-24 13:23 ` rguenth at gcc dot gnu.org
` (4 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: wilco at gcc dot gnu.org @ 2023-07-24 13:09 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110791
Wilco <wilco at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |wilco at gcc dot gnu.org
--- Comment #4 from Wilco <wilco at gcc dot gnu.org> ---
Simpler example:
void f(void);
void bug (char *path, char *p)
{
while( p > path && p[-1] == '/' )
p--;
if (p < path)
f();
}
bug:
subs r3, r1, r0
cmp r0, r1
add r3, r3, #1
bhi .L7
adds r0, r0, #1
bne .L5
.L7:
movs r3, #1
.L5:
subs r3, r3, #1
bne .L2
bcc .L3 ** this is obviously never taken
bx lr
.L2:
ldrb r2, [r1, #-1]! @ zero_extendqisi2
cmp r2, #47
beq .L5
bx lr
.L3:
b f
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug rtl-optimization/110791] [12/13/14 Regression] arm: Wrong code with -Os -march=armv8.1-m.main
2023-07-24 10:51 [Bug rtl-optimization/110791] New: [12/13/14 Regression] arm: Wrong code with -Os -march=armv8.1-m.main acoplan at gcc dot gnu.org
` (3 preceding siblings ...)
2023-07-24 13:09 ` wilco at gcc dot gnu.org
@ 2023-07-24 13:23 ` rguenth at gcc dot gnu.org
2023-07-24 14:39 ` acoplan at gcc dot gnu.org
` (3 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: rguenth at gcc dot gnu.org @ 2023-07-24 13:23 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110791
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|--- |12.4
Keywords| |needs-bisection
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug rtl-optimization/110791] [12/13/14 Regression] arm: Wrong code with -Os -march=armv8.1-m.main
2023-07-24 10:51 [Bug rtl-optimization/110791] New: [12/13/14 Regression] arm: Wrong code with -Os -march=armv8.1-m.main acoplan at gcc dot gnu.org
` (4 preceding siblings ...)
2023-07-24 13:23 ` rguenth at gcc dot gnu.org
@ 2023-07-24 14:39 ` acoplan at gcc dot gnu.org
2023-07-24 15:14 ` [Bug middle-end/110791] " wilco at gcc dot gnu.org
` (2 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: acoplan at gcc dot gnu.org @ 2023-07-24 14:39 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110791
Alex Coplan <acoplan at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords|needs-bisection |
--- Comment #5 from Alex Coplan <acoplan at gcc dot gnu.org> ---
Thanks Wilco for the simpler example.
It seems to have started with
r13-1268-g8c99e307b20c502e55c425897fb3884ba8f05882 with both of these
testcases, but it's probably a latent issue elsewhere (since it doesn't seem to
show up on other targets). Needs more analysis.
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug middle-end/110791] [12/13/14 Regression] arm: Wrong code with -Os -march=armv8.1-m.main
2023-07-24 10:51 [Bug rtl-optimization/110791] New: [12/13/14 Regression] arm: Wrong code with -Os -march=armv8.1-m.main acoplan at gcc dot gnu.org
` (5 preceding siblings ...)
2023-07-24 14:39 ` acoplan at gcc dot gnu.org
@ 2023-07-24 15:14 ` wilco at gcc dot gnu.org
2024-03-07 23:28 ` [Bug rtl-optimization/110791] [12/13/14 Regression] arm: Wrong code with -Os -march=armv8.1-m.main (maybe fmodulo-sched related) law at gcc dot gnu.org
2024-06-20 9:13 ` [Bug rtl-optimization/110791] [12/13/14/15 " rguenth at gcc dot gnu.org
8 siblings, 0 replies; 10+ messages in thread
From: wilco at gcc dot gnu.org @ 2023-07-24 15:14 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110791
Wilco <wilco at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
Component|rtl-optimization |middle-end
Status|UNCONFIRMED |NEW
--- Comment #6 from Wilco <wilco at gcc dot gnu.org> ---
(In reply to Alex Coplan from comment #5)
> Thanks Wilco for the simpler example.
>
> It seems to have started with
> r13-1268-g8c99e307b20c502e55c425897fb3884ba8f05882 with both of these
> testcases, but it's probably a latent issue elsewhere (since it doesn't seem
> to show up on other targets). Needs more analysis.
The bug happens on all targets with -fmodulo-sched -Os, eg. AArch64:
bug:
sub x2, x1, x0
add x2, x2, 1
cmp x0, x1
bhi .L7
cmn x0, #1
bne .L9
.L7:
mov x2, 1
.L9:
subs x2, x2, #1
beq .L1
ldrb w0, [x1, -1]
cmp w0, 47
beq .L6
.L1:
ret
.L6:
sub x1, x1, #1
b .L9
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug rtl-optimization/110791] [12/13/14 Regression] arm: Wrong code with -Os -march=armv8.1-m.main (maybe fmodulo-sched related)
2023-07-24 10:51 [Bug rtl-optimization/110791] New: [12/13/14 Regression] arm: Wrong code with -Os -march=armv8.1-m.main acoplan at gcc dot gnu.org
` (6 preceding siblings ...)
2023-07-24 15:14 ` [Bug middle-end/110791] " wilco at gcc dot gnu.org
@ 2024-03-07 23:28 ` law at gcc dot gnu.org
2024-06-20 9:13 ` [Bug rtl-optimization/110791] [12/13/14/15 " rguenth at gcc dot gnu.org
8 siblings, 0 replies; 10+ messages in thread
From: law at gcc dot gnu.org @ 2024-03-07 23:28 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110791
Jeffrey A. Law <law at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Priority|P3 |P4
CC| |law at gcc dot gnu.org
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug rtl-optimization/110791] [12/13/14/15 Regression] arm: Wrong code with -Os -march=armv8.1-m.main (maybe fmodulo-sched related)
2023-07-24 10:51 [Bug rtl-optimization/110791] New: [12/13/14 Regression] arm: Wrong code with -Os -march=armv8.1-m.main acoplan at gcc dot gnu.org
` (7 preceding siblings ...)
2024-03-07 23:28 ` [Bug rtl-optimization/110791] [12/13/14 Regression] arm: Wrong code with -Os -march=armv8.1-m.main (maybe fmodulo-sched related) law at gcc dot gnu.org
@ 2024-06-20 9:13 ` rguenth at gcc dot gnu.org
8 siblings, 0 replies; 10+ messages in thread
From: rguenth at gcc dot gnu.org @ 2024-06-20 9:13 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110791
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|12.4 |12.5
--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 12.4 is being released, retargeting bugs to GCC 12.5.
^ permalink raw reply [flat|nested] 10+ messages in thread
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2023-07-24 10:51 [Bug rtl-optimization/110791] New: [12/13/14 Regression] arm: Wrong code with -Os -march=armv8.1-m.main acoplan at gcc dot gnu.org
2023-07-24 11:24 ` [Bug rtl-optimization/110791] " xry111 at gcc dot gnu.org
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2024-03-07 23:28 ` [Bug rtl-optimization/110791] [12/13/14 Regression] arm: Wrong code with -Os -march=armv8.1-m.main (maybe fmodulo-sched related) law at gcc dot gnu.org
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