Thoughts about semantics of BB_VISITED

[Zdenek Dvorak]

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.

> In any case, I agree that we should assert this inside verify_flow_info. 
>  I'll prepare a patch.

Thanks.

Zdenek