Re: [RFC] CFG hooks for rtl/tree specificities

[Jan Hubicka <jh at suse dot cz>]

> > 
> > > This seems to be different from tree-ssa one where for instance basic
> > > block removeal does not appear to take care to kill the surrouding
> > > control flow constructs, just kill the contained statements.  
> > > 
> > > I am not sure how much of the API we can map - I was looking at the edge
> > > splitting code and don't quite understand how it preserves the CFG
> > > consistent with the tree representation. 
> > The BB that splits the edge is artificial, and thus it does not have to 
> > modify the underlying representation.  
> 
> What exactly do you mean by artifical BB?
> > 
> > > I.E when the new basic block is
> > > created there is no modification into underlying IL made and I have no
> > > idea how you do decide wehre to place code that eventually will be
> > > inserted into the BB.  
> > 
> > I would say that this is the job of the bsi_insert*-ers.  
> > It would be interesting to have this interface also at RTL level: 
> > ie. insertions performed with the help of iterators using 
> > bsi_insert_after, bsi_insert_before, and bsi_insert_on_edge.
> 
> Hmm, I see, bsi_insert_on_edge called on edge between two abstract
> blocks will call bsi_insert_after on iterator containing the empty block
> that will in turn look for the followup block that is again empty block
> and abort ().
> 
> It also appears to fail in the case the edge is in between abstract
> block and normal block that starts at a label and this edge comes from
> goto statement, while the label can be also reached via fallthru.
> In that case bsi_insert_after appears to insert code at the beggining of
> parent stmt of the destination block that may be well before the
> label and thus it is reached by the other ede than it is supposed to.

Hi,
I was looking bit more on the bsi code and it is very interesting :) I
wonder what operations can be implemented this way without running into
inexpected dead ends.  Is there some other compiler using similar
approach in practice I can look on too?

Honza