Thoughts about semantics of BB_VISITED

[Daniel Berlin]

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