[RFC, PATCH]: Introduction of callgraph annotation class

[Richard Biener]

On Wed, Oct 15, 2014 at 6:26 PM, Martin Liška <mliska@suse.cz> wrote:
> Hello.
>
> Following patch introduces a new class called callgraph_annotation. Idea
> behind the patch is to provide a generic interface one can use to register
> custom info related to a cgraph_node. As you know, symbol_table provides
> hooks for creation, deletion and duplication of a cgraph_node. If you have a
> pass, you need to handle all these hooks and store custom data in your data
> structure.
>
> As an example, after discussion with Martin, I chose usage in ipa-prop.h:
>
> data structure:
> vec<ipa_node_params> ipa_node_params_vector
>
> if the pass handles an event, following chunk is executed:
> if (ipa_node_params_vector.length () <= (unsigned) symtab->cgraph_max_uid)
>     ipa_node_params_vector.safe_grow_cleared (symtab->cgraph_max_uid + 1);
>
> The problem is that you can have sparse UIDs of cgraph_nodes and every time
> you have to allocate a vector of size equal to cgraph_max_uid.
>
> As a replacement, I implemented first version of cgraph_annotation that
> internally uses hash_map<cgraph_unique_identifier, T>.
> Every time a node is deleted, we remove corresponding data associated to the
> node.
>
> What do you think about it?

I don't like "generic annotation" facilities at all.  Would it be possible
to make cgraph UIDs not sparse?  (keep a free-list of cgraph nodes
with UID < cgraph_max_uid, only really free nodes at the end)
Using a different data structure than a vector indexed by cgraph UID
should also be easily possible (a map from UID to data, hash_map <int, T>).

Richard.

> Thank you,
> Martin