RFR: 8186670: Implement _onSpinWait() intrinsic for AArch64 [v2]

[Andrew Haley]

On Tue, 21 Sep 2021 13:14:05 GMT, Evgeny Astigeevich <github.com+42899633+eastig at openjdk.org> wrote:

>> src/hotspot/cpu/aarch64/aarch64.ad line 14374:
>> 
>>> 14372:         ShouldNotReachHere();
>>> 14373:     }
>>> 14374:     #undef EMIT_N_ASM_STRINGS
>> 
>> None of this is necessary. Printing "onspinwait" is enough.
>
> This results no instructions implementing `onspinwait` in OptoAssembly output. Why do we want to hide the details?

It's not useful as a verification that the correct instructions were generated: you need a disassembly for that. OptoAssembly is usually a somewhat briefer format.

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