Re: Thoughts about semantics of BB_VISITED

[Daniel Berlin <dberlin at dberlin dot org>]

On Fri, 7 Jan 2005, Diego Novillo wrote:

> Zdenek Dvorak wrote:
> > Hello,
> >
> >
> > > > If the state of the mark would be undefined, you would need either to
> > > > clean them up first (over whole cfg), or use bitmaps for the marks.
> > > > Both of these approaches bring a risk of quadratic behavior.
> > >
> > > Quadratic behaviour?  How?
> >
> >
> > because the places where it is used now (most notably, get_loop_body)
> > do not look at whole cfg, but just at the loop body.
> Oh, I see.  So, this is inside a helper, not a pass.  How unfortunate. 
> Perhaps get_loop_body should not use BB_VISITED.  What if the pass calling 
> get_loop_body is using BB_VISITED for its own processing?

Then you get screwed, because it clears the visited flags when it's done 
(see dfs_enumerate_from).


Also note that get_loop_body_in_dom_order doesn't touch the visited flags.

Whatever get_loop_body does to visited flags should at the very least be 
documented.

--Dan