RFR(XL): JDK-8228441 Field layout requires complete overhaul to efficiently support inline classes

Tobias Hartmann tobias.hartmann at oracle.com
Fri Jul 26 12:50:31 UTC 2019

Hi Fred,

just wondering, did you intentionally include the change in compile.cpp? If so, it should be guarded
by #ifdef ASSERT but I would suggest to just remove it.

Best regards,

On 19.07.19 17:26, Frederic Parain wrote:
> Greetings,
> This is the initial request for review for a new code to layout fields.
> The current code to compute field layouts is especially ugly and
> not fitted to efficiently flatten inline classes.
> This changeset is an almost complete overhaul of the field layout code,
> with a new framework to compute layouts and two different allocation
> strategies (one for identity classes and one for inline classes).
> CR: https://bugs.openjdk.java.net/browse/JDK-8228441
> Webrev: http://cr.openjdk.java.net/~fparain/layout/webrev.00/
> This changeset also includes some options and DCMD to ease inspection
> of layouts, especially when flattenable fields are involved.
> The changeset doesn’t remove the old layout code, meaning that either
> the old code or the new code can be used (controlled by VM flag).
> This code passed tiers 1 to 3 on Valhalla supported platforms.
> Some failures have been identified in higher tiers with some @Contended
> tests, but they are due to test bugs (tests making relying on wrong
> assumptions about field layouts).
> The code contains a lot of comments about the new framework and the
> different allocation strategies. Feel free to complain if comments
> are not clear enough or if some code need more comments.
> Regarding the huge size of this changeset, and people being in summer
> vacation, I’m not planning to push this code in the short term.
> Thank you,
> Fred

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