Feature request #2

allow aliasing between in/out reg ptr arguments (update in-place)

Goal

Sometimes, the checks performed at the callee sites by the Jasmin compiler enforcing non-aliasing between input and output reg ptr arguments are a bit too strict. Specifically, in the following function:

fn _bn_mulm ( reg ptr u64[NLIMBS] a b r ) -> reg ptr u64[NLIMBS] {
  stack u64[NLIMBS] tmp;
  stack u64[2*NLIMBS] tmp2;
  tmp2 = __bn_muln(a, b, tmp2);
  r = __bn_rdcn(tmp2, r, tmp);
  return r;
}

the compiler rejects a call _bn_mulm(a, b, a), but it would in fact be ok -- all the reads from a occur prior to the write in r. The workaround would be to write a new version for update in-place:

fn _bn_mulmU ( reg ptr u64[NLIMBS] a b ) -> reg ptr u64[NLIMBS] {
  stack u64[NLIMBS] tmp;
  stack u64[2*NLIMBS] tmp2;
  tmp2 = __bn_muln(a, b, tmp2);
  a = __bn_rdcn(tmp2, a, tmp);
  return a;
}

It would be nice if we were able to avoid these redundant versions, by relaxing the check.