The following is a very simplified pb that appeared in ruby.
Any attempt to simplify the example makes the bug disappear.

Minimal optimization for the bug to appear:
  -O2 -fomit-frame-pointer

The bug is "x" being put in the stack for "f" as the second argument, not
the
first one ("f" is a tail-call)



--------------------------------------------------------------------------------
void raise(long) __attribute__ ((noreturn));

long f(double);

long g(long i, double x)
{
  if (x < 0) raise(1);
  return f(x);
}
--------------------------------------------------------------------------------

The test prints "0" when it should print "2"
--------------------------------------------------------------------------------
void raise (long e) { exit(0); }

long f(double i) {
  printf("%g\n", i);
  return 0;
}

long g(long i, double x);

main() {
  g(0, 2.0);
}