speed of invokeExact

[Jochen Theodorou]

Am 07.05.2013 19:31, schrieb Christian Thalinger:
[...]
> Do you have any numbers?The problem is that if the MH is not constant
> we can't do any inlining  and it will be an out-of-line call (with a trampoline in between). Is
> your DMH a static or virtual?

arg... looks like I made a mistake. It is not the invokeExact that is 
slow, it is my preparation of the handle that is slow.

I get the arguments as Object[] so I do:
         >         MethodHandle mh = 
call.target.asSpreader(Object[].class, call.args.length);
>         mh = MethodHandles.insertArguments(mh, 0, call.receiver);
>         mh = mh.asType(VC);

I found this code doesn't really make sense in my case, since the 
arguments length is 0. But even if I replace it by

>         MethodHandle mh = MethodHandles.dropArguments(call.target, 1, Object[].class);
>         mh = MethodHandles.insertArguments(mh, 0, call.receiver);
>         mh = mh.asType(VC); //VC= Object[]:Object

it takes long. It improved in my test from 15000 to 3000. The only 
problem is that my old way still takes only a fraction of that. In 3000 
I can not only do the invocation plus adaption for the call, I can even 
do full method selection... and it still totals to only about 200. And 
of that 3000 an estimated 2900 goes into adapting the handle.

Now I am a bit unsure of how to get this better. The problem is that I 
have such an invokeExact path in Groovy today already. It is called the 
first time the handle is selected and in case of a callsite that does 
not cached, or that got invalidated. In a typical microbenchmark that 
situation may not appear often, but in a general application it does.

In further experiments I used spreadInvoker, which did help to get times 
down to 1500

>         MethodHandle mh = MethodHandles.spreadInvoker(call.target.type(), call.args.length+1);
>         mh = mh.asType(VC) //VC= MethodHandle,Object,Object[]:Object

but I cannot get rid of the asType call in my generic code. If I use 
casts to force the right types and don't use asType I get about 250

bye blackdrag

-- 
Jochen "blackdrag" Theodorou - Groovy Project Tech Lead
blog: http://blackdragsview.blogspot.com/
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