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

[Brian Goetz]

Add a comment to LMF to remember to update the hack if additional sigs are added.  

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> On Feb 20, 2018, at 4:27 AM, Claes Redestad <claes.redestad at oracle.com> wrote:
> 
> You also pointed out that if the params or return types doesn't match, we'd get a CCE sooner or later, making the return and argument checks superfluous. This all simplifies into this, then:
> 
> http://cr.openjdk.java.net/~redestad/8198418/jdk.02/
> 
> Thanks!
> 
> /Claes
> 
> 
>> On 2018-02-20 13:20, Vladimir Ivanov wrote:
>> No need in MT.equals. Pointer comparison should work as well: MethodType instances are interned and all exact type checks on MethodHandles are implemented using == on their MTs.
>> 
>> Best regards,
>> Vladimir Ivanov
>> 
>>> On 2/20/18 3:07 PM, Claes Redestad wrote:
>>> Hi Rémi,
>>> 
>>> sure, MethodType.equals will do a fast == check, but then checks the param types. It sure looks cleaner, though:
>>> 
>>> http://cr.openjdk.java.net/~redestad/8198418/jdk.01/
>>> 
>>> Thanks!
>>> 
>>> /Claes
>>> 
>>> 
>>>> On 2018-02-20 12:38, Remi Forax wrote:
>>>> 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
>>> 
>