[PATCH, RFC] Introduce -fsanitize=use-after-scope

[Martin Liška]

Hello.

One more issue I forgot to mention in the previous email:
e) As one can come up with a source code which jumps to a label within
a block scope (use-after-scope-goto-1.c):

// { dg-do run }
// { dg-additional-options "-fsanitize=use-after-scope -fstack-reuse=none" }

int main(int argc, char **argv)
{
  int a = 123;

  if (argc == 0)
  {
    int *ptr;
    label:
      {
	ptr = &a;
        *ptr = 1;
	return 0;
      }
  }
  else
    goto label;

  return 0;
}

It's necessary to record all local variables in gimplifier and possibly
emit unpoisoning code when a LABEL_EXPR is seen. That results in following gimple
output:

label:
  _20 = (unsigned long) &a;
  _21 = (unsigned long) 4;
  __builtin___asan_unpoison_stack_memory (_20, _21);
  _22 = (unsigned long) &ptr;
  _23 = (unsigned long) 8;
  __builtin___asan_unpoison_stack_memory (_22, _23);
  ptr = &a;
  ptr.0_10 = ptr;
  _24 = (unsigned long) ptr.0_10;
  _25 = _24 >> 3;
  _26 = _25 + 2147450880;
  _27 = (signed char *) _26;
  _28 = *_27;
  _29 = _28 != 0;
  _30 = _24 & 7;
  _31 = (signed char) _30;
  _32 = _31 + 3;
  _33 = _32 >= _28;
  _34 = _29 & _33;
  if (_34 != 0)
    goto <bb 5>;
  else
    goto <bb 6>;

I know that the solution is a big hammer, but it works.

Martin