https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109609
--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Oh the problem is related to tail calls:
strncpy (&dst, ptr_30, 23); [tail call]
That should not be marked as a tail call as buf is still alive during the call
of strncpy.
Simple workaround, add
asm("":::"memory");
Right before the end of invert.
Or use -fno-optimize-sibling-calls
Self contained testcase:
```
#define N 23
#define MAX_LEN 13
char dst[N + 1];
void invert(const char *id) {
char buf[MAX_LEN];
char *ptr = buf + sizeof(buf); // start from the end of buf
*(--ptr) = '\0'; // terminate string
while (*id && ptr > buf) {
*(--ptr) = *(id++); // copy id backwards
}
__builtin_strncpy(dst, ptr, N); // copy ptr/buf to dst
// asm("":::"memory"); // This "fixes" the issue.
}
int main() {
invert("abcde");
if (strcmp(dst, "edcba"))
__builtin_abort();
}
```
