We're out of tree codes; now what?

[Mike Stump]

On Mar 13, 2007, at 5:29 AM, Doug Gregor wrote:
> I don't know if we'll be able to get rid of *enough* tree codes,  
> without going to some kind of two-level hierarchy.

I think we can.  I have a patch, that in theory should work (doesn't  
bootsrap yet, not sure why).  I use subcodes for all the Objective-C  
TYPE nodes.

> Some upcoming bits that will need more tree codes:
>  - C++0x (my guess: > 10 new tree codes),

If we decide to subcode, we're going to have to have reject patches  
that add any new codes without removing codes on a one for one basis.

> If trees were only used by the middle end, or only used by the
> C/C++/Objective C/C++ front ends, we'd be okay. But we decided to use
> them in both places.

Actually, if we keep the front-end data structures away from the mid- 
end and/or back-end, we can use the same values in the codes between  
the front-end and the rest of the compiler.  This would potentially  
give us back many codes, without the _cost_ of subcodes.  The  
downside, printers (debug_tree) of codes would have to be away from  
which realm the code came from to print it.