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

[Andrew Haley]

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.

You might be over-thinking this a little. You already check that the assembler macro does the right thing, so as long as you've made sure the C1 code actually calls the macro you're good. Also, this is a performance-only change (does not affect correctness) and it may not have a great deal of affect in C1-generated code anyway.

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