Polimorphic vs Megamorphic calls

[forax at univ-mlv.fr]

This remember me that i should enroll Aleksey to do the same for the basic strategies based on invokedynamic used by the dynamic languages.

Rémi

----- Mail original -----
> De: "Dawid Weiss" <dawid.weiss at gmail.com>
> À: "Remi Forax" <forax at univ-mlv.fr>
> Cc: "Ionut" <ionutb83 at yahoo.com>, "Hotspot-dev Developers" <hotspot-dev at openjdk.java.net>
> Envoyé: Mercredi 30 Mars 2016 19:19:51
> Objet: Re: Polimorphic vs Megamorphic calls
> 
> Aleksey has a very nice and relevant blog post about it:
> http://shipilev.net/blog/2015/black-magic-method-dispatch/
> 
> Dawid
> 
> On Wed, Mar 30, 2016 at 5:12 PM, Remi Forax <forax at univ-mlv.fr> wrote:
> > ----- Mail original -----
> >> De: "Ionut" <ionutb83 at yahoo.com>
> >> À: "Hotspot-dev Developers" <hotspot-dev at openjdk.java.net>
> >> Envoyé: Mardi 29 Mars 2016 10:32:40
> >> Objet: Polimorphic vs Megamorphic calls
> >>
> >> Hello All,
> >
> > Hi,
> >
> >>    Could you please explain what is the difference between a Polimorphic
> >>    and a Megamorphic call?
> >
> > It's a dynamic property of a method call instruction (invokeinterface and
> > invokevirtual in the Java bytecode).
> > This is related to an optimization technique called inlining-cache [1],
> > For Hotspot,
> >  - if the instruction has always been called the same method
> >  implementation, the callsite is monomorphic,
> >    and the inlining cache is just a comparison and a jump,
> >  - if the instruction has been called a small number of method
> >  implementations (for Hotspot, it's 2),
> >    the inlining cache do several comparison/jump checks.
> >  - if the instruction has been called with a lot of different
> >  implementations,
> >    there is no inlining cache, a virtual call [2] is generated instead.
> >
> >
> >> If you have some documentation on this topic or how it is handled by
> >> HotSpot would be great.
> >
> > There is a wiki, (not updated as i should be)
> >
> > https://wiki.openjdk.java.net/display/HotSpot/PerformanceTechniques
> > (see sections Profiling, Deoptimization, Methods)
> >
> >
> >> Regards,
> >> Ionut
> >
> > Rémi
> >
> > [1] https://en.wikipedia.org/wiki/Inline_caching
> > [2] https://wiki.openjdk.java.net/display/HotSpot/VirtualCalls
>