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* [Bug tree-optimization/96007] New: -O2 miscompiles memcmp an object with a string literal containing '\0'
@ 2020-06-30 15:10 jerryfromearth at gmail dot com
2020-06-30 15:17 ` [Bug tree-optimization/96007] " jakub at gcc dot gnu.org
` (5 more replies)
0 siblings, 6 replies; 7+ messages in thread
From: jerryfromearth at gmail dot com @ 2020-06-30 15:10 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96007
Bug ID: 96007
Summary: -O2 miscompiles memcmp an object with a string literal
containing '\0'
Product: gcc
Version: 9.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: jerryfromearth at gmail dot com
Target Milestone: ---
Hi,
While comparing an object to a literal string that contains "\0" (e.g.
memcmp((&u128), "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0", 16)), -O2 produces
incorrect result, while -O1 and -O0 produces correct result.
This affects at least gcc 9.2, 9.3 and 10.1.
gcc 9.1 is fine.
```
$ cat test.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct tagMYUINT128
{
unsigned long u64High;
unsigned long u64Low;
} MYUINT128, *PMYUINT128;
int main(int argc, char **argv) {
MYUINT128 u128 = {0};
char arr[] = "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0";
printf("All results are expected to be non-zero.\n");
// Test A, u128={0x0, 0x1234}
printf("Test A. u128={0x0, 0x1234}\n");
u128.u64High = 0x0;
u128.u64Low = 0x1234;
// Comparing to a literal string is broken.
printf("memcmp1 result=%d\n", memcmp((&u128),
"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0", 16));
printf("memcmp2 result=%d\n", __builtin_memcmp((&u128),
"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0", 16));
// Comparing to a array pointer works.
printf("memcmp3 result=%d\n", memcmp((&u128), arr, 16));
printf("memcmp4 result=%d\n", __builtin_memcmp((&u128), arr, 16));
return 0;
}
$ gcc -O2 -o test test.c && ./test
All results are expected to be non-zero.
Test A. u128={0x0, 0x1234}
memcmp1 result=0
memcmp2 result=0
memcmp3 result=52
memcmp4 result=52
$ gcc -O1 -o test test.c && ./test
All results are expected to be non-zero.
Test A. u128={0x0, 0x1234}
memcmp1 result=52
memcmp2 result=52
memcmp3 result=52
memcmp4 result=52
```
godbolt link: https://godbolt.org/z/9M3L8h (it contains more tests)
I looked into the list of bugs fixed in 9.2 and found this probably relevant
issue:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90892
Cheers,
Jiarui Hong
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug tree-optimization/96007] -O2 miscompiles memcmp an object with a string literal containing '\0'
2020-06-30 15:10 [Bug tree-optimization/96007] New: -O2 miscompiles memcmp an object with a string literal containing '\0' jerryfromearth at gmail dot com
@ 2020-06-30 15:17 ` jakub at gcc dot gnu.org
2020-06-30 15:34 ` marxin at gcc dot gnu.org
` (4 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: jakub at gcc dot gnu.org @ 2020-06-30 15:17 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96007
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jakub at gcc dot gnu.org
--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Perhaps related/dup to PR95189?
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug tree-optimization/96007] -O2 miscompiles memcmp an object with a string literal containing '\0'
2020-06-30 15:10 [Bug tree-optimization/96007] New: -O2 miscompiles memcmp an object with a string literal containing '\0' jerryfromearth at gmail dot com
2020-06-30 15:17 ` [Bug tree-optimization/96007] " jakub at gcc dot gnu.org
@ 2020-06-30 15:34 ` marxin at gcc dot gnu.org
2020-06-30 16:14 ` msebor at gcc dot gnu.org
` (3 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: marxin at gcc dot gnu.org @ 2020-06-30 15:34 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96007
Martin Liška <marxin at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
Assignee|unassigned at gcc dot gnu.org |marxin at gcc dot gnu.org
Status|UNCONFIRMED |ASSIGNED
CC| |marxin at gcc dot gnu.org
Last reconfirmed| |2020-06-30
--- Comment #2 from Martin Liška <marxin at gcc dot gnu.org> ---
This one started with my r10-1545-g6aa2e42cb4be16ee, so let me take a look.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug tree-optimization/96007] -O2 miscompiles memcmp an object with a string literal containing '\0'
2020-06-30 15:10 [Bug tree-optimization/96007] New: -O2 miscompiles memcmp an object with a string literal containing '\0' jerryfromearth at gmail dot com
2020-06-30 15:17 ` [Bug tree-optimization/96007] " jakub at gcc dot gnu.org
2020-06-30 15:34 ` marxin at gcc dot gnu.org
@ 2020-06-30 16:14 ` msebor at gcc dot gnu.org
2020-07-01 6:28 ` marxin at gcc dot gnu.org
` (2 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: msebor at gcc dot gnu.org @ 2020-06-30 16:14 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96007
Martin Sebor <msebor at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |msebor at gcc dot gnu.org
--- Comment #3 from Martin Sebor <msebor at gcc dot gnu.org> ---
I suspect it's the same thing -- see bug 95189 comment #7. I've got a patch in
testing.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug tree-optimization/96007] -O2 miscompiles memcmp an object with a string literal containing '\0'
2020-06-30 15:10 [Bug tree-optimization/96007] New: -O2 miscompiles memcmp an object with a string literal containing '\0' jerryfromearth at gmail dot com
` (2 preceding siblings ...)
2020-06-30 16:14 ` msebor at gcc dot gnu.org
@ 2020-07-01 6:28 ` marxin at gcc dot gnu.org
2020-07-01 6:49 ` [Bug tree-optimization/96007] [9/10/11 Regression] " rguenth at gcc dot gnu.org
2020-07-01 14:46 ` [Bug middle-end/96007] " msebor at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: marxin at gcc dot gnu.org @ 2020-07-01 6:28 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96007
Martin Liška <marxin at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Assignee|marxin at gcc dot gnu.org |msebor at gcc dot gnu.org
--- Comment #4 from Martin Liška <marxin at gcc dot gnu.org> ---
All right, leaving to you Martin.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug tree-optimization/96007] [9/10/11 Regression] -O2 miscompiles memcmp an object with a string literal containing '\0'
2020-06-30 15:10 [Bug tree-optimization/96007] New: -O2 miscompiles memcmp an object with a string literal containing '\0' jerryfromearth at gmail dot com
` (3 preceding siblings ...)
2020-07-01 6:28 ` marxin at gcc dot gnu.org
@ 2020-07-01 6:49 ` rguenth at gcc dot gnu.org
2020-07-01 14:46 ` [Bug middle-end/96007] " msebor at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: rguenth at gcc dot gnu.org @ 2020-07-01 6:49 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96007
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |wrong-code
Priority|P3 |P2
Summary|-O2 miscompiles memcmp an |[9/10/11 Regression] -O2
|object with a string |miscompiles memcmp an
|literal containing '\0' |object with a string
| |literal containing '\0'
Target Milestone|--- |9.4
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug middle-end/96007] [9/10/11 Regression] -O2 miscompiles memcmp an object with a string literal containing '\0'
2020-06-30 15:10 [Bug tree-optimization/96007] New: -O2 miscompiles memcmp an object with a string literal containing '\0' jerryfromearth at gmail dot com
` (4 preceding siblings ...)
2020-07-01 6:49 ` [Bug tree-optimization/96007] [9/10/11 Regression] " rguenth at gcc dot gnu.org
@ 2020-07-01 14:46 ` msebor at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: msebor at gcc dot gnu.org @ 2020-07-01 14:46 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96007
Martin Sebor <msebor at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Component|tree-optimization |middle-end
Resolution|--- |DUPLICATE
Status|ASSIGNED |RESOLVED
--- Comment #5 from Martin Sebor <msebor at gcc dot gnu.org> ---
The patch for pr95189 fixes this as well. Resolving as a duplicate.
*** This bug has been marked as a duplicate of bug 95189 ***
^ permalink raw reply [flat|nested] 7+ messages in thread
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2020-06-30 15:10 [Bug tree-optimization/96007] New: -O2 miscompiles memcmp an object with a string literal containing '\0' jerryfromearth at gmail dot com
2020-06-30 15:17 ` [Bug tree-optimization/96007] " jakub at gcc dot gnu.org
2020-06-30 15:34 ` marxin at gcc dot gnu.org
2020-06-30 16:14 ` msebor at gcc dot gnu.org
2020-07-01 6:28 ` marxin at gcc dot gnu.org
2020-07-01 6:49 ` [Bug tree-optimization/96007] [9/10/11 Regression] " rguenth at gcc dot gnu.org
2020-07-01 14:46 ` [Bug middle-end/96007] " msebor at gcc dot gnu.org
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