Re: [lto] Stop using void_list_node in equality comparisons.

[Kazu Hirata <kazu at codesourcery dot com>]

Hi Mark,

> > This patch changes those functions to expect void_type_node in
> > TREE_VALUE of the last TREE_LIST node.  This way, it is OK for one of
> > my conversion patches to introduce TYPE_ARG_TYPES that ends with a
> > TREE_LIST node (!= void_list_node) whose TREE_VALUE is still
> > void_type_node.
>
>
> Why do you want to do that?  The point of void_list_node is that it
> reduces waste.  Almost every function will have a parameter type list
> that ends with void, so it is good to share the node.
>
> (Of course, a better representation would just be to have a varargs_p
> bit on the FUNCTION_TYPE; it's goofy to have a void type at the end of
> the list.  But, that would be another major cleanup, so we don't want to
> do it now.)

Yes, void_list_node reduces waste, but we are not going to need it because it 
uses TREE_LIST.  My patch to change the low-level representation will introduce 
void_vec_node, which is an instance of TREE_VEC with nothing but void_type_node 
in it, but it will not be used as frequently as void_list_node because 
void_list_node applies to every function with a fixed number of parameters, 
whereas void_vec_node applies to functions with no parameters.

Kazu Hirata