RFR: 8186670: Implement _onSpinWait() intrinsic for AArch64 [v8]

[Evgeny Astigeevich]

On Wed, 29 Sep 2021 06:44:29 GMT, Christian Hagedorn <chagedorn at openjdk.org> wrote:

>> The [IR test framework](https://github.com/openjdk/jdk/blob/master/test/hotspot/jtreg/compiler/lib/ir_framework/README.md) can parse the C2 opto assembly output, and also control compilation level and flags through method annotations. I'm not sure if we could use that to check the C1 output though. Maybe @chhagedorn has some ideas?
>
> The framework only supports regex matching on C2's ideal and opto assembly output. You would still need the current checks for C1's output. So, I'm not sure if it's worth transforming the C2 checks only to use the framework.

> The [IR test framework](https://github.com/openjdk/jdk/blob/master/test/hotspot/jtreg/compiler/lib/ir_framework/README.md) can parse the C2 opto assembly output, and also control compilation level and flags through method annotations. I'm not sure if we could use that to check the C1 output though. Maybe @chhagedorn has some ideas?

I wrote a test using the IR test framework. The framework checks the output of `-XX:+PrintIdeal -XX:+PrintOptoAssembly`.  It cannot check what instructions and how many of them have been emitted. It can only check onSpinWait is intrinsified and the format of the intrinsic.
I think the framework needs to support the output of `PrintAssembly`.

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