Rewrite: array.length op= e2 as: array.length = array.length op e2 or: auto tmp = &array; (*tmp).length = (*tmp).length op e2
Helper function for easy error propagation. If error occurs, returns ErrorExp. Otherwise returns NULL.
Mark the operand as will never be dereferenced, which is useful info for @safe checks. Do before semantic() on operands rewrites them.