https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92955
--- Comment #5 from Martin Sebor <msebor at gcc dot gnu.org> ---
An even simpler test case. Changing the index in g() to unsigned avoids the
warning.
$ cat pr92955.c && gcc -O3 -S -Wall pr92955.c
typedef struct S { unsigned char n, a[4]; } S;
void f (S *s, const unsigned char *p, int n)
{
int i = n < 0 ? 0 : n;
while (*p)
s->a[i++] = *p++; // no warning (good)
}
void g (S *s, const unsigned char *p, int n)
{
int i;
for (i = 0; i < n; ++i);
while (*p)
s->a[i++] = *p++; // spurious -Wstringop-overflow
}
pr92955.c: In function ‘g’:
pr92955.c:18:15: warning: writing 1 byte into a region of size 0
[-Wstringop-overflow=]
18 | s->a[i++] = *p++; // spurious -Wstringop-overflow
| ~~~~~~~~~~^~~~~~
pr92955.c:1:37: note: at offset [4, 2147483647] to object ‘a’ with size 4
declared here
1 | typedef struct S { unsigned char n, a[4]; } S;
| ^
