Inlining heuristic trouble

[Mark Roos]

Thanks for the example Rémi

Out of curiosity why is the fallback method synchronized?  Something to do 
with SwitchPoints?

thanks
mark




From:
Rémi Forax <forax at univ-mlv.fr>
To:
mlvm-dev at openjdk.java.net
Date:
06/21/2011 12:28 AM
Subject:
Re: Inlining heuristic trouble
Sent by:
mlvm-dev-bounces at openjdk.java.net



On 06/21/2011 12:27 AM, John Rose wrote:
> On Jun 20, 2011, at 1:11 PM, Mark Roos wrote:
>
>> So we do not have a path that can be assumed to be not taken (except 
the last in the chain).
>>
>> Perhaps in the JVM this is a poor choice for implementation of a small 
polymorphic inline cache.  Here I defer to the real experts
> Both monomorphic and polymorphic inline caches are a central use case 
for invokedynamic.  For more details and references, see the VMIL paper 
linked here:
>    http://blogs.oracle.com/jrose/entry/vmil_paper_on_invokedynamic
>
> See section 5, "Case Study: Inline Caches and invokedynamic".
>
> A small (non-megamorphic) polymorphic cache can be represented as a 
cascade or decision tree of GWT combinators, probably with a control block 
of some sort that can rebalance from time to time.
>
> A megamorphic call site can be represented using the class pattern of a 
two-step dispatch plus indirect function call. The foldArguments 
combinator is intended to support this pattern.  (You fold some arguments 
together, yielding a MH to prepend to the argument list, and then you jump 
to an invoker.)  This can support vtable or metaclass dispatches, or more 
subtle ones like the CLOS dispatch via a hash of relevant argument 
attributes.
>
> (I'm getting hungry for Remi's cookbook, because it will have this sort 
of example in it nicely worked out.)

The bi-morphic inlining cache is the example you're looking for:
http://code.google.com/p/jsr292-cookbook/source/browse/trunk/bimorphic-cache/src/jsr292/cookbook/bicache/RT.java


It first creates a tree of GWTs and if there are more than two possible 
classes/targets for one callsite,
it create a dispatch table* + foldArguments (around line 42).

> -- John

Rémi
* the current implementation uses a synchronized map but I have an 
immutable version on my laptop,
I have to do some perf test.

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