code: private void changeBody(ImmutableMap<Integer, String> argNames) {
      for (Node ref : currentArgumentsAccesses) {
        Node index = ref.getNext();
        Node parent = ref.getParent();
        int value = (int) index.getDouble(); // This was validated earlier.
  
        @Nullable String name = argNames.get(value);
        if (name == null) {
          continue;
        }
  
        Node newName = IR.name(name).useSourceInfoIfMissingFrom(parent);
        parent.replaceWith(newName);
        // TODO(nickreid): See if we can do this fewer times. The accesses may be in different scopes.
        compiler.reportChangeToEnclosingScope(newName);
      }
    }
docs: Performs the replacement of arguments[x] -> a if x is known.
  
  @param argNames maps param index to param name, if the param with that index has a name.