[11] RFR: 8198418: Invoke LambdaMetafactory::metafactory exactly from the BootstrapMethodInvoker

[Remi Forax]

Hi Claes,
instead of checking each parameter of the bsmType(), why not allocating the corresponding MethodType and storing it in a static final, so you can check if the MethodType are equals using equals (as far as i remember MethodType.equals is a == in the OpenJDK implementation).

in term of name why not isLambdaMetafactoryIndyBootstrapMethod and isLambdaMetafactoryCondyBoostrapMethod instead of isLambdaMetafactoryCallSite and isLambdaMetafactoryFunction ?

and you can remove <T> in the signature of isLambdaMetafactoryCallSite() and replace Class<T> by Class<?>.

cheers,
Rémi

----- Mail original -----
> De: "Claes Redestad" <claes.redestad at oracle.com>
> À: "core-libs-dev" <core-libs-dev at openjdk.java.net>
> Envoyé: Mardi 20 Février 2018 11:51:15
> Objet: [11] RFR: 8198418: Invoke LambdaMetafactory::metafactory exactly from the BootstrapMethodInvoker

> Hi,
> 
> a small regression to lambda bootstrapping came in with the recent
> condy merge, and it took me a while to figure out why.
> 
> Before condy, the first three parameters of calls from the BSM invoker
> to the six parameter LambdaMetafactory::metafactory were statically
> known, so only the fourth through sixth param were dynamically bound
> to enforce runtime type checks (MH.invoke -> MH.checkGenericInvoker
> -> MH.asType(MT) -> MHI.makePairwiseConvertByEditor -> generates a
> slew of filterArguments, rebinds, casting MHs etc).
> 
> With condy, the third parameter is now an Object (in reality either a
> Class or a MethodType), thus not statically known. This means the
> MethodType sent to checkGenericInvoker will have to add a cast for
> this param too, thus in makePairwiseConvertByEditor we see an
> additional rebind, some additional time spent spinning classes etc.
> Effectively increasing the cost of first lambda initialization by a small
> amount (a couple of ms).
> 
> Here came the realization that much of the static overhead of the
> lambda bootstrapping could be avoided altogether since we can
> determine and cast arguments statically for the special-but-common
> case of LambdaMetafactory::metafactory. By using exact type
> information, and even bootstrapMethod.invokeExact, no dynamic
> runtime checking is needed, so the time spent in
> makePairwiseConvertByEditor is avoided entirely.
> 
> This might be a hack, but a hack that removes a large chunk of the
> code executed (~75% less bytecode) for the initial lambda bootstrap.
> Startup tests exercising lambdas show a 10-15ms improvement - the
> static overhead of using lambdas is now just a few milliseconds in total.
> 
> Webrev: http://cr.openjdk.java.net/~redestad/8198418/jdk.00/
> RFE: https://bugs.openjdk.java.net/browse/JDK-8198418
> 
> The patch includes a test for an experimental new metafactory method
> that exists only in the amber condy-folding branch. I can easily break it
> out and push that directly to amber once this patch syncs up there, but
> have tested that keeping it in here does no harm.
> 
> Thanks!
> 
> /Claes