RFR: 8349146: [REDO] Implement a better allocator for downcalls

[Chen Liang]

On Wed, 23 Apr 2025 14:05:58 GMT, Per Minborg <pminborg at openjdk.org> wrote:

> This PR is based on the work of @mernst-github and aims to implement an _internal_ thread-local 'stack' allocator, which works like a dynamically sized arena, but with reset functionality to reset the allocated size back to a certain level. The underlying memory could stay around between calls, which could improve performance.
> 
> Re-allocated segments are not zeroed between allocations.

Looks to be in parity with the original patch.

Can we just cleanly revert commit 77647421c5b13738f6fa145bf30cbb9dd741e164?
This new version defines redundant sealed interface + record - feels unnecessary to me.
Meanwhile, the BufferStackBench is valueable, but its addition should be kept in a separate commit to make reviewing easier.

`trust_final_non_static_fields` in `ciField` already trusts `jdk.internal.foreign`, so I don't think the record performance argument stands here. But making Frame and BufferStack classes final is a good move.

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Marked as reviewed by liach (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/24829#pullrequestreview-2788100611
PR Comment: https://git.openjdk.org/jdk/pull/24829#issuecomment-2824546993
PR Comment: https://git.openjdk.org/jdk/pull/24829#issuecomment-2824731824