RFR: 8305895: Implement JEP 450: Compact Object Headers (Experimental) [v21]

[Thomas Stuefe]

On Thu, 24 Oct 2024 09:54:05 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

> As I understand the comment, it says alignment <= cache line size. But the implementation makes alignment >= cache line size. "hyper alignment" means alignment > cache line size?

Correct. since encoding range must cover the full klass range, and we only have 22bit nklass, shift is larger. at most 10. but since that causes hyper aligning, we try to get away with smaller shifts if klass range is smaller.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20677#discussion_r1814680330