[Bug middle-end/109609] [12/13/14 Regression] tail call for function even when passing a ptr which references a local array still

[gburca-gnu at ebixio dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109609

--- Comment #7 from Gabriel Burca <gburca-gnu at ebixio dot com> ---
Here's the code that still fails with -O3 -fno-optimize-sibling-calls:

```
#include <string.h>
#include <stdint.h>
#define N 23
#define MAX_LEN 13
char dst[N + 1];

void stringify(uint64_t 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) = static_cast<char>(id % 10) + '0';
    id /= 10;
  }
  __builtin_strncpy(dst, ptr, N);           // copy ptr/buf to dst
}

int main() {
  stringify(12345);
  if (strcmp(dst, "12345"))
    __builtin_abort();
}
```

Notably this only fails with -O3, not with -O2