[lilliput-jdk17u:lilliput] Integrated: 8303771: [Lilliput/JDK17] Fix interpreter asymmetric fast-locking

[Roman Kennke]

On Tue, 7 Mar 2023 20:49:27 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

> Backport of https://github.com/openjdk/lilliput/pull/76.
> 
> Currently we get the asymmetric locking check in the interpreters wrong:
> 
> ldr(header_reg, Address(rthread, JavaThread::lock_stack_current_offset()));
> cmpoop(header_reg, obj_reg);
> br(Assembler::NE, slow_case);
> 
> The intention is to load the top of the lock-stack, and compare it to the unlocked object, and, if not equal, branch to the slow-path to handle it. However, what it really does is, it loads the *address* of the top of lock-stack, and compares that to the unlocked object. This can never succeed, and therefore we always call the slow-path. Additionally, the address is not the address of the topmost object, it is the address of the next free slot. What we really want to load is the element at -1 oop from that address. This is not incorrect, but it's unnecessarily slow.
> 
> Testing:
>  - [x] tier1 (x86_64, x86_32, aarch64)
>  - [ ] tier2 (x86_64, x86_32, aarch64)

This pull request has now been integrated.

Changeset: 6f12bf95
Author:    Roman Kennke <rkennke at openjdk.org>
URL:       https://git.openjdk.org/lilliput-jdk17u/commit/6f12bf956f35badace8494298f1579395848f071
Stats:     7 lines in 2 files changed: 4 ins; 0 del; 3 mod

8303771: [Lilliput/JDK17] Fix interpreter asymmetric fast-locking

Reviewed-by: stuefe

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PR: https://git.openjdk.org/lilliput-jdk17u/pull/9