https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103956
Bug ID: 103956
Summary: [10 Regression] -Wstringop-overflow= false positive on
-O3 for writes to array
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: martin at martin dot st
Target Milestone: ---
Since GCC 10.0, the following snippet produces warnings (various numbers of
warnings with the same issue) for this reduced snippet:
$ cat repro.c
struct data {
unsigned char array[10];
};
void copy(struct data *data, unsigned char *src, int n) {
int i;
for (i = 0; i < n; i++)
data->array[i] = src[i];
}
$ gcc -c -O3 repro.c
repro.c: In function 'copy':
repro.c:7:20: warning: writing 1 byte into a region of size 0
[-Wstringop-overflow=]
7 | data->array[i] = src[i];
| ~~~~~~~~~~~~~~~^~~~~~~~
repro.c:2:17: note: at offset 10 into destination object 'array' of size 10
2 | unsigned char array[10];
| ^~~~~
It doesn't reproduce at -O2.
The issue is also testable on Compiler Explorer:
https://godbolt.org/z/xsc3K37jK
