RFR: 8305896: Alternative full GC forwarding [v12]

[Erik Österlund]

On Thu, 4 May 2023 10:50:17 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

>> If you wouldn't mind, I think this one is even better: https://github.com/iwanowww/jdk/blob/ssc.cascading/src/hotspot/share/oops/klass.cpp?plain=1#L309
>> @iwanowww is using it for faster type checking. Our very own @rose00 is behind this one, so we can definitely use it. It performs very well (~1ns per hash). The hash algo passes BigCrush (as a CBPNRG) and SMhasher (with the right loop to combine the input blocks). It's basically a fantastic hash function, that we are free to use.
>
> Ok that is great stuff! Maybe it'd be useful to move it to a central place with this PR (alternative full GC fwding), because we're going to need it for other purposes, too (other GC tables, i-hash, faster type checking, maybe more?)
> 
> Oh and that code is using __int128 type, how/where do I get that outside of GCC?

Yes - great idea. Maybe somewhere in utilities. We might swap to it with ZGC as well when things settle down there.

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PR Review Comment: https://git.openjdk.org/jdk/pull/13582#discussion_r1184860529