RFR: 8319901: Recursive lightweight locking: ppc64le implementation

[Martin Doerr]

On Fri, 10 Nov 2023 13:21:58 GMT, Axel Boldt-Christmas <aboldtch at openjdk.org> wrote:

> Draft implementation of recursive lightweight JDK-8319796 for ppc64le.
> 
> Porters feel free to discard this and implement something from scratch, take this initial draft and run with it, or send patches to me and if you want me to drive the PR.
> 
> Some notes:
> ppc64le deviates from the other ports, it shares it C2 locking code with the native call wrapper. This draft unifies the behavior across the ports by using the C1/interpreter locking for native call wrapper. If it is important to have a fast path for the inflated monitor case for native call wrapper, it could be done without having it share its implementation with C2. 
> It would also be possible to change this behavior on all ports (share the C2 code), as I believe the C2 assumptions always hold for the native call wrapper, the monitor exit and monitor enter will be balanced and structured.

Thanks a lot! LGTM.

Regarding aarch64: Should we file a JBS issue for the usage of `box`?
https://github.com/openjdk/jdk/blob/d31fd78d963d5d103b1b1bf66ae0bdbe4be2b790/src/hotspot/cpu/aarch64/aarch64.ad#L16470
has no kill effect for `box`, but `C2_MacroAssembler::fast_lock_lightweight` kills it. It may be never used, but it's a trap someone might run into. x86_64 uses `USE_KILL box`.

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Marked as reviewed by mdoerr (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/16611#pullrequestreview-1892100633