Re: Thoughts about semantics of BB_VISITED

[Daniel Berlin <dberlin at dberlin dot org>]

On Fri, 7 Jan 2005, 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 it is doomed :-(.  Quite often there is no real reason why a pass
> should use BB_VISITED -- it can simply use sbitmap of basic blocks instead.

Why can't one just pass an sbitmap to get_loop_body, instead of it 
destroying visited flags without telling you?

--Dan