RFR: 8291555: Replace stack-locking with fast-locking [v3]

[Roman Kennke]

On Tue, 11 Oct 2022 13:25:30 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Roman Kennke has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - Merge remote-tracking branch 'origin/fast-locking' into fast-locking
>>  - Re-use r0 in call to unlock_object()
>
> src/hotspot/cpu/aarch64/c1_LIRAssembler_aarch64.cpp line 272:
> 
>> 270:     // SharedRuntime::OSR_migration_begin() packs BasicObjectLocks in
>> 271:     // the OSR buffer using 2 word entries: first the lock and then
>> 272:     // the oop.
> 
> This comment is now irrelevant?

Yes, removed it there and in same files in other arches.

> src/hotspot/cpu/aarch64/c1_LIRAssembler_aarch64.cpp line 432:
> 
>> 430:   if (method()->is_synchronized()) {
>> 431:     monitor_address(0, FrameMap::r0_opr);
>> 432:     __ ldr(r4, Address(r0, BasicObjectLock::obj_offset_in_bytes()));
> 
> Do we have to use a new register here, or can we just reuse `r0`?

r0 is used below in call to unlock_object(), but not actually used there. I shuffled it a little and re-use r0 now.

> src/hotspot/cpu/aarch64/sharedRuntime_aarch64.cpp line 1886:
> 
>> 1884: 
>> 1885:     __ mov(c_rarg0, obj_reg);
>> 1886:     __ mov(c_rarg1, rthread);
> 
> Now that you dropped an argument here, you need to do `__ call_VM_leaf` with `2`, not with `3` arguments?

Good catch! Yes.

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PR: https://git.openjdk.org/jdk/pull/10590