CHA for interfaces in C2 compiler

[Remi Forax]

On 04/15/2015 04:10 PM, Vitaly Davidovich wrote:
> Hi guys,
>
> So CHA on classes works nicely in the case of only one subtype 
> loaded.  What about interfaces? Currently, it looks like no such 
> optimization/analysis is done.  In my experience, there's a 
> substantial amount of code that exposes an interface via some API, but 
> then loads only implementation of it.  The interface is used instead 
> of abstract class to allow more flexibility in the future.
>
> I fully realize that lots of interfaces have more than 1 implementer 
> loaded at runtime, but I also think it's worthwhile to attempt CHA for 
> them.
>
> Is this something that's feasible to do? It would require more class 
> loading dependencies to be tracked, but I'm also fine with having this 
> be an extra flag that I can use to enable/disable this optimization.
>
> Thoughts?
>
> Thanks

I've implemented something like this in a language (which has a special 
syntax for calling Java object).
To avoid to have too many metadata, I've used a simple heuristic, the 
idea is that an interface with a lot of methods do not have a lot of 
implementations so the runtime only tried to do CHA, using a 
SwitchPoint, if there were more than 3 methods (included) in the interface.

cheers,
Rémi