Re: [PATCH] Empty redirect_edge_var_map after each pass and function

[Jeff Law <law@redhat.com>]

On 12/02/2015 01:33 AM, Richard Biener wrote:
>> Right.  So the question I have is how/why did DOM leave anything in the map.
>> And if DOM is fixed to not leave stuff lying around, can we then assert that
>> nothing is ever left in those maps between passes?  There's certainly no good
>> reason I'm aware of why DOM would leave things in this state.
>
> It happens not only with DOM but with all passes doing edge redirection.
> This is because the map is populated by GIMPLE cfg hooks just in case
> it might be used.  But there is no such thing as a "start CFG manip"
> and "end CFG manip" to cleanup such dead state.
Sigh.

>
> IMHO the redirect-edge-var-map stuff is just the very most possible
> unclean implementation possible. :(  (see how remove_edge "clears"
> stale info from the map to avoid even more "interesting" stale
> data)
>
> Ideally we could assert the map is empty whenever we leave a pass,
> but as said it triggers all over the place.  Even cfg-cleanup causes
> such stale data.
>
> I agree that the patch is only a half-way "solution", but a full
> solution would require sth more explicit, like we do with
> initialize_original_copy_tables/free_original_copy_tables.  Thus
> require passes to explicitely request the edge data to be preserved
> with a initialize_edge_var_map/free_edge_var_map call pair.
>
> Not appropriate at this stage IMHO (well, unless it turns out to be
> a very localized patch).
So maybe as a follow-up to aid folks in the future, how about a 
debugging verify_whatever function that we can call manually if 
debugging a problem in this space.  With a comment indicating why we 
can't call it unconditionally (yet).


jeff