[tree-ssa] Garbage collector x bb annotations

[Zdenek Dvorak]

Hello,

> > > > I have just run into the following problem: dom_children get released by
> > > > ggc_collect call in tree-ssa-pre.  Allocating them by ggc seems wrong to
> > > > me, since basic block annotations are allocated from obstack and
> > > > invisible to garbage collector.
> > > > 
> > > Yeah.  But there's more than that, unfortunately.  All the fields in
> > > struct bb_ann_d are ggc allocated.  The real solution would be to
> > > finally convert basic blocks to ggc.  Volunteers?
> > 
> > I may try (I need it anyway for tree-ssa-cfg branch).  The whole issue
> > is however quite ugly as this combines basically all allocation
> > mechanisms that are available in gcc (basic blocks themselves are pool
> > allocated).
> 
> It's not that ugly to make the fix, you simply have to throw out all
> those other allocation mechanisms and use ggc.

that's not really a good idea.  Their purpose is to improve data
locality, and changing this would slow down things.

Zdenek