[master] RFR: 8347710: [Lilliput] Implement 4 byte headers [v8]

[Roman Kennke]

On Mon, 27 Jan 2025 10:57:58 GMT, Andrew Dinn <adinn at openjdk.org> wrote:

> Is there ever a time when we have an acquiring load on a narrow klass pointer?

I don't think so, but I copied it from the original loadNKlass code.

> Also, do we ever generate code which loads a narrow klass pointer from something other than an Object? Maybe there's a use somewhere of `LoadNKlass` from somewhere other than `obj-start + klass_offset_in_bytes`?

No, I don't think so, I've checked the C2 code for that. Any paths that load from non-objects are using LoadKlass.

That said, I would love to have a cleaner way to load the (narrow) Klass* out of an object. There has been some discussion around that problem earlier: https://bugs.openjdk.org/browse/JDK-8340453

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PR Review Comment: https://git.openjdk.org/lilliput/pull/193#discussion_r1930425913