[tree-ssa] Garbage collector x bb annotations

[Daniel Berlin]

>
> :-) But really, getting things slower just because we are lazy to write
> 10 more lines of code is not a great idea.  I agree there is a terrible
> mess in memory allocation in gcc, and having this all done by garbage
> collector would be great, but we should first have a good one (btw. 
> what
> I always wondered -- is there not somewhere floating some decent free
> garbage collector that could be used?)

Boehm's is slower than what we've got now.

I'm working on hybrid copying + mark and sweep.

If you *really* want to improve the gc, however, we need compiler 
support.
--Dan