for the assignments introduced by the inliner to assign the actuals
to the formals. Since the assignment is on the boundary (LHS from the
callee, RHS from the caller), either position could be used. But,
(1) picking the caller's makes it easier to map back to the source from
the generated code and (2) is arguably more useful since the RHS is
the interesting part of the operation and may be a complex expression.
