[tree-ssa][ GC, Virtual operands, and GCing between passes

[Andrew MacLeod]

On Tue, 2003-12-09 at 18:36, Geoff Keating wrote:
> Andrew MacLeod <amacleod@redhat.com> writes:
> 
> > Are we sure we want to GC between passes? :-|
> > 
> > since VDEFs and VUSEs are tree nodes, I can't allocate the structure
> > which holds them anywhere except GC'd memory can I?
> > 
> > ie
> > 
> > a_3 = VDEF <a_2>
> > 
> > This requires points to 2 trees.
> > 
> > the GC system has to know not to collect the trees I am pointing to in
> > the 2 words of the vdef vector.
> > 
> > but I dont want to GC the vdef vector.
> 
> Why not?
> 
Ok, so assuming I do it all in GCable form, 

I have array of pointers to trees.

so 

tree **defs;

I don't want what defs points to to be marked, since they are marked
otherwise, I just need the defs vector itself collected:

typedef struct def_optype_d GTY(())
{
  unsigned num_defs;
  tree ** GTY((skip(""))) defs;
} def_optype_t;

If I use skip like this, it doesnt do anything does it?  meaning it
doesnt free defs?

typedef struct def_optype_d GTY(())
{
  unsigned num_defss;
  tree **GTY((length ("%h.num_defs"))) defs;
} vdef_optype_t;

I can tell it how long the vector is but then it claims it doesnt
understand the type "tree **", so it aborts.

Should it look like:

typedef struct def_optype_d GTY(())
{
  unsigned num_defs;
  tree ** GTY((length ("%h.num_vuses"),skip(""))) defs;
} def_optype_t;


or what do I need to do?

Andrew