Feature Request: nontrivial functions and vtable optimizations

[davidl]

在 Tue, 12 Aug 2008 16:45:08 +0800，downs <default_357-line at yahoo.de> 写道:

> The overhead of vtable calls is well known.
>
> For this reason, it may be worthwhile to include an optimization that  
> essentially checks if a certain class is only inherited from a few  
> times, like, <= three, in the visible program, and if so, replace vtable  
> calls with a tree of classinfo pointer comparisons and direct function  
> calls.
>
> When I did this manually in some hobbyist path tracing code, I gained  
> significant speed-ups, even though I didn't collect any hard numbers.
>
> So, for instance, the equivalent D code would look like so:
>
> class A { ... } class B : A { ... } class C : A { ... }
>
> A a = genSomeObj();
> // a.test();
> if (a.classinfo == typeid(B)) (cast(B)cast(void*) a).test(); // call as  
> if final
> else if (a.classinfo == typeid(C)) (cast(C)cast(void*) a).test(); // dito
> else a.test(); // fallback
>
> Ideas?

It's better to show your benchmark examples, there people can observe and  
discuss

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