[master] RFR: 8307991: [Lilliput] Use narrow i-hash only when +UseCompactObjectHeaders

[Aleksey Shipilev]

On Fri, 12 May 2023 10:33:45 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

> Currently, we use a narrow 25bit identity-hash-code in Lilliput. That is even the case when running without compact object headers, even though we could just as well use the original 31bit identity hash-code then.
> 
> The fix is relatively simple. Also, this brings the code in line with what we're currently proposing in upstream https://github.com/openjdk/jdk/pull/13844.
> 
> Going forward we would trade Klass* bits to get the full 31 i-hash back, and we're going to do that soon, but let's first fix this issue at hand (also in preparation for a clean backport, where we don't currently have the metaspace improvements).
> 
> Testing:
>  - [x] tier1 +UseCompactObjectHeaders
>  - [ ] tier2 +UseCompactObjectHeaders
>  - [x] tier1 -UseCompactObjectHeaders
>  - [ ] tier2 -UseCompactObjectHeaders

Looks good.

-------------

Marked as reviewed by shade (Committer).

PR Review: https://git.openjdk.org/lilliput/pull/93#pullrequestreview-1424749351