deduplicating lambda methods

[Maurizio Cimadamore]

In other words, what I'm saying is that the key should be 
DynamicMethodSymbol, and that we should avoid creating multiple DMS for 
callsites which have the same properties. That reflects also invariant 
in javac: symbols are shared (where possible). A similar point holds for 
class literals, which are modeled as field access to a fictional symbol 
called 'class' - we should no creating that fictional symbol multiple 
times, there should be some shared Scope or similar structure somewhere 
which, given a class C, gives you back the .class symbol associated with C.

Maurizio


On 29/03/18 15:00, Maurizio Cimadamore wrote:
>
>
> On 29/03/18 11:32, B. Blaser wrote:
>> On 28 March 2018 at 23:51, B. Blaser <bsrbnd at gmail.com> wrote:
>>> On 28 March 2018 at 20:09, Maurizio Cimadamore
>>> <maurizio.cimadamore at oracle.com> wrote:
>>>> To me this seems to suggest that, if we want to get better results 
>>>> out of
>>>> the dedup machinery, we have to up our lowering game, so that we 
>>>> don't do
>>>> excessive generation of fresh symbols. Right now we don't cache .class
>>>> symbols and also metafactory calls with same static args and BSM - and
>>>> that's the problem you are seeing, I believe.
>>> You're right. The fix below tries to cache meta-factory calls, solving
>>> the following de-duplication problem:
>>>      r1 = () -> {
>>>          Runnable r2 = () -> {};
>>>      };
>> Running javac tests, I note that the cache key isn't precise enough.
>> Any idea of what a good key would be?
> I think the key has to take into account:
>
> * name and type of BSM method
> * dynamic type of the indy call
> * values of all static args
>
> just using the lambda impl name would not cut it, esp. if 
> deduplication is turned on (as the same lambda impl will be reused 
> e.g. for a Function<Integer, Integer> and a Function<String, String> - 
> of the underlying lambda is the identity x -> x ).
>
> Maurizio
>>
>> Bernard
>>
>>
>>> Bernard
>>>
>>> diff -r 9925be430918
>>> src/jdk.compiler/share/classes/com/sun/tools/javac/comp/LambdaToMethod.java 
>>>
>>> --- 
>>> a/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/LambdaToMethod.java
>>>     Wed Mar 28 14:24:17 2018 +0100
>>> +++ 
>>> b/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/LambdaToMethod.java
>>>     Wed Mar 28 23:24:59 2018 +0200
>>> @@ -226,6 +226,8 @@
>>>
>>>           private Map<DedupedLambda, DedupedLambda> dedupedLambdas;
>>>
>>> +        private Map<Name, DynamicMethodSymbol> dynMethSyms = new 
>>> HashMap<>();
>>> +
>>>           /**
>>>            * list of deserialization cases
>>>            */
>>> @@ -1220,7 +1222,8 @@
>>> staticArgs.toArray());
>>>
>>>               JCFieldAccess qualifier =
>>> make.Select(make.QualIdent(site.tsym), bsmName);
>>> -            qualifier.sym = dynSym;
>>> +            DynamicMethodSymbol existing =
>>> kInfo.dynMethSyms.putIfAbsent(methName, dynSym);
>>> +            qualifier.sym = existing != null ? existing : dynSym;
>>>               qualifier.type = indyType.getReturnType();
>>>
>>>               JCMethodInvocation proxyCall = make.Apply(List.nil(),
>>> qualifier, indyArgs);
>>>
>>>> Maurizio
>>>>
>>>>> Bernard
>>>>>
>>>>>> Maurizio
>