redirect_edge_and_branch questions

[Andrew MacLeod]

On Fri, 2004-10-01 at 17:49, Zdenek Dvorak wrote:
> Hello,
> 
> > Perhaps it would make sense to have function that takes list of
> > incomming edges to given basic block and create empty basic block before
> > redirecting the selected edges into it.  This operatinon should be
> > usefull at least for creating loop preheaders.
> 
> and its name is "make_forwarder_block" :-)
> 

What do I have to do with the parameter 
   void (*new_bb_cbk) (basic_block))

? Its not documented, and I see where it is used in cfg_loop.c calls
"update_latch" which allocated aux entries, sets a dominator, etc.  What
am I suppose to do in there? Can I do nothing or is there a minimum I
must do? 

It looks like I don't have to even provide that routine since NULL is
always returned by tree_redirect_edge_branch_and_force().  Is this true?

Andrew