Compressed Class Pointers

[Remi Forax]

----- Original Message -----
> From: "Julian Waters" <tanksherman27 at gmail.com>
> To: lilliput-dev at openjdk.java.net
> Sent: Sunday, May 29, 2022 2:37:15 PM
> Subject: Compressed Class Pointers

> Hi all,
> 
> Apologies for the sudden noise in the list, but I've come to notice that
> Lilliput seems to be enforcing Compressed Class Pointers if the running
> HotSpot VM happens to be 64-bit. (
> https://github.com/openjdk/lilliput/blob/9f4a50febc483a342ef09ac0c08f6d742857178d/src/hotspot/share/oops/oop.inline.hpp#L99
> )
> 
> I'm admittedly a little behind on the work done with Lilliput, so I'm not
> entirely sure what the rationale behind this choice is, is there anywhere I
> could go to for a little catching up? (Alternatively Compressed Class
> Pointers aren't actually being enforced, and I'm mistakenly missing
> something else)
> 
> best regards,
> Julian


Hi Julian,

The aim of liliput is to reduce the size of the object header, to either 64 bits or better 32 bits if possible.

If a class pointer is 64 bits == the size of a non compressed pointer on a 64 bits VM, the game is already lost.

regards,
Rémi