For the following code, gcc trunk at -O2 emits wrong code. If you run the compiled code multiple times, you will observe different outputs.

$ cat a.c
int printf(const char *, ...);
char a;
int b;
short c;
short(d)(short e) { return e + c; }
int f;
char g;
char g_0;
int h;
void i() {
  for (; h; f++)
    switch (g_0)
    case '"':
    case '\\':
      ++g;
}
short j;
static int aa;
int k;
const int *l;
const int **m = &l;
short n;
signed o;
int p = 84134051;
unsigned r = 1;
int ag;
static char ah() {
  int ai = 0;
  if (r)
  aj : {
    i();
    short *ak = &n;
    ag = 78003764;
    *m = &ag;
    *ak = 1;
    for (; *l + p - 162153904 + k; k++)
      for (; p - 168260671 > 3; ai++) {
        *ak = o && 5;
        if (a) {
          int *al = &aa;
          short *am = &j;
          *al &= b;
          *am = 0;
        }
      }
    if (d((*ak)--))
      ;
    else if (*l)
      goto aj;
  }
    return 0;
}
int main() {
  ah();
  printf("%d\n", n);
}
$
$ gcc-tk -O0 a.c && ./a.out
0
$ gcc-tk -O2 a.c
$ ./a.out
518
$ ./a.out
514
$
$ gcc-tk -v
Using built-in specs.
COLLECT_GCC=gcc-tk
COLLECT_LTO_WRAPPER=/zdata/shaoli/compilers/ccbuilder-compilers/gcc-27612ce352921d74086102d9ad4d3e011923f837/libexec/gcc/x86_64-pc-linux-gnu/14.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../configure --disable-multilib --disable-bootstrap --enable-languages=c,c++ --prefix=/zdata/shaoli/compilers/ccbuilder-compilers/gcc-27612ce352921d74086102d9ad4d3e011923f837
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 14.0.0 20230616 (experimental) (GCC) 
$