speed of invokeExact

[Christian Thalinger]

On May 10, 2013, at 1:37 AM, Jochen Theodorou <blackdrag at gmx.org> wrote:

> Am 10.05.2013 02:40, schrieb Christian Thalinger:
> [...]
>> That's because your method handle is not constant and so the compiler cannot inline the call.
> 
> And you tell me that in the first case the call was inlined?

No.  I was referring to your comment about "hotspot should throw out the invocation completely, but it does not".  That's the case in both examples.

> That is 
> unexpected. And if that is the case, then why does this:
> 
>>>>        MethodHandle mh = MethodHandles.lookup().findVirtual(String.class, "toString", MethodType.methodType(String.class));
>>>>        MethodType invokeType = MethodType.methodType(Object.class, String.class);
>>>>        int tmax = 1_000_000;
>>>>        for (int k=0; k<20; k++) {
>>>>            long t1 = System.nanoTime();
>>>>            for (int i=0; i<tmax; i++) {
>>>>                MethodHandle invoker = mh.asType(invokeType);
>>>>            }
>>>>            long t2 = System.nanoTime();
>>>>            System.out.println((t2-t1)/tmax);
>>>>        }
> 
> take that long as well? Maybe it changed, but I thought only handles 
> coming from a final field are constant enough for inlining. If I compare 
> to 1.7.11 (or 1.7.6) then I get around 23 for the first, and 200-300 for 
> the second and third test. That is about a factor 10-15 slowdown, that 
> is what I would expect from the call not being inlined for example. But 
> I always thought 1.7 will not inline in this case at all. On my 1.8 it 
> was almost a factor 100. So unless the noninlined call on a method 
> handle got extremely expensive compared to 1.7, there must be something 
> else too.

I haven't looked but maybe the slowdown is because the asType call cannot be inlined completely and so the compiler doesn't know it always returns the same result.

-- Chris

> 
> bye blackdrag
> 
> -- 
> Jochen "blackdrag" Theodorou - Groovy Project Tech Lead
> blog: http://blackdragsview.blogspot.com/
> german groovy discussion newsgroup: de.comp.lang.misc
> For Groovy programming sources visit http://groovy-lang.org
> 
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