[Bug c/71598] Wrong optimization with aliasing enums

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71598

--- Comment #12 from Richard Biener <rguenth at gcc dot gnu.org> ---
Created attachment 45973
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=45973&action=edit
patch I am testing

I am testing the following.  I needed to adjust the testcase a bit to make
the C++ FE happy, in particular casting the arguments to the function to
pointer-to-enum type and storing an enum member rather than an integer
(the conversion on the return stmts seems to work):

enum e1 { c1 };

__attribute__((noinline,noclone))
int f(enum e1 *p, unsigned *q)
{
  *p = c1;
  *q = 2;
  return *p;
}

int main()
{
  unsigned x;

  if (f((enum e1 *)&x, &x) != 2)
    __builtin_abort();
  return 0;
}