[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).

Zdenek