differentiation

In operations_broadcast_test.go there are some tests that are not yet filled in. The point is to test that broadcasting works for different shapes. The semantics of broadcast probably isn't clear, so please do send me a message for anything.

This is a good first issue for anyone looking to get interested

Minimum reproducible example:

float func(float z, int a) { 
  for (int i = 1; i < a; i++){
    z = z * a;
  }
  return z;
}

results in the following failed assertion

```Assertion `(isGenericMethod || ((*I)->isVariablyModifiedType() || (*I).getNonReferenceType()->isObjCRetainableType() || getContext() .getCanonicalType((*I).getNonReferenceType()) .getTypePtr() == getContex