Fwd: Adding Valhalla bits to Lilliput headers

[John Rose]

FYI, here’s a discussion we are having in Valhalla about its requirements on the object header, and how we envision adjusting to Lilliput.

There is no immediate action required by Lilliput, but you can keep our requirements in mind for when the matter ripens.  It probably affects the way Lilliput thinks about further compression of class IDs.

https://mail.openjdk.org/pipermail/valhalla-dev/2023-May/011051.html

Forwarded message:

From: John Rose <john.r.rose at oracle.com>
To: valhalla-dev at openjdk.java.net
Subject: Adding Valhalla bits to Lilliput headers
Date: Thu, 11 May 2023 11:23:09 -0700

Since Lilliput is becoming very real (yay!) the question arises, how will Valhalla be impacted, if at all?

Since we use object header bits for special new state (4 at current count), we will need to rethink how those work with Lilliput’s reorganization of that same header.

Here are a few thoughts on this set of problems:

https://cr.openjdk.org/~jrose/values/valhalla-and-lilliput.html
https://cr.openjdk.org/~jrose/values/valhalla-and-lilliput.md

Comments?  Anything I should add or remove?

— John