RFR: 8186670: Implement _onSpinWait() intrinsic for AArch64 [v3]

[Evgeny Astigeevich]

On Tue, 21 Sep 2021 22:22:50 GMT, Evgeny Astigeevich <github.com+42899633+eastig at openjdk.org> wrote:

>> This PR is a follow-up on the discussion [“RFC: AArch64: Implementing spin pauses with ISB”](https://mail.openjdk.java.net/pipermail/hotspot-dev/2021-August/054033.html).
>> 
>> It adds the option `OnSpinWaitImpl=value`, where `value` can be:
>> 
>> - `none`: no implementation for spin pauses. This is the default value.
>> - `Nnop`: use `nop` instruction for spin pauses. Optional `N` can be `2..9` to specify a number of `nop` instructions.
>> - `Nisb`: use `isb` instruction for spin pauses. Optional `N` can be `2..9` to specify a number of `isb` instructions.
>> - `Nyield`: use `yield` instruction for spin pauses. Optional `N` can be `2..9` to specify a number of `yield` instructions.
>> 
>> The code for the `Thread.onSpinWait` intrinsic is generated based on the value of `OnSpinWaitImpl`.
>> 
>> Testing:
>> 
>> - `make test TEST="gtest"`: Passed
>> - `make run-test TEST="tier1"`: Passed
>> - `make run-test TEST="tier2"`: Passed
>> - `make run-test TEST=hotspot/jtreg/compiler/onSpinWait`: Passed
>
> Evgeny Astigeevich has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Move emitting code to MacroAssembler::spin_wait
>   
>   Code emitting spin pauses is moved to MacroAssembler::spin_wait.
>   As OptoAssembly output is changed, tests are updated to parse
>   PrintAssembly.

@theRealAph, when I was writing a test I notice a strange thing in `PrintAssembly` output:

# {method} {0x0000ffff6ac00370} 'test' '()V' in 'compiler/onSpinWait/TestOnSpinWaitImplAArch64$Launcher'
  #           [sp+0x40]  (sp of caller)
  0x0000ffff9d557680: 1f20 03d5 | e953 40d1 | 3f01 00f9 | ff03 01d1 | fd7b 03a9 | 1f20 03d5 | 1f20 03d5 | 1f20 03d5
  0x0000ffff9d5576a0: 1f20 03d5 | 1f20 03d5 | 1f20 03d5

  0x0000ffff9d5576ac: ;*invokestatic onSpinWait {reexecute=0 rethrow=0 return_oop=0}
                      ; - compiler.onSpinWait.TestOnSpinWaitImplAArch64$Launcher::test at 0 (line 161)
  0x0000ffff9d5576ac: 1f20 03d5 | fd7b 43a9 | ff03 0191


The code is for the case when 7 NOPs are used for a spin pause.
In the output only one instruction is after `invokestatic onSpinWait`. Other 6 instructions are before it.
Is it expected behaviour or a bug?

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PR: https://git.openjdk.java.net/jdk/pull/5562