[jdk15u-dev] RFR: 8186670: Implement _onSpinWait() intrinsic for AArch64

[Paul Hohensee]

On Wed, 23 Feb 2022 15:43:41 GMT, Evgeny Astigeevich <duke at openjdk.java.net> wrote:

> A backport of a configurable implementation of _onSpinWait() intrinsic to achieve parity with x86 which has it implemented.
> The risk of changes is low. By default it is off.
> Tested for fastdebug and release builds:
> 
> - `gtest`: Passed
> - `tier1`...`tier3`: Passed except [JDK-8261534](https://bugs.openjdk.java.net/browse/JDK-8261534) and [JDK-8277488](https://bugs.openjdk.java.net/browse/JDK-8277488)
> - `hotspot/jtreg/compiler/onSpinWait`: Passed
> 
> Applying the patch had issues to find proper positions. No code changes are needed after repositioning.
> Changes to `globals_aarch64.hpp` needed the new added options definitions to be converted from the new format to the old one. `vm.flagless` was removed from the new tests. 
> Changes to `vm_version_aarch64.cpp`, instantiation of `SpinWait`, use C++11 syntax. They needed to be changed to C++03 syntax.

I skipped right over the {} vs ()!

Lgtm.

-------------

Marked as reviewed by phh (Reviewer).

PR: https://git.openjdk.java.net/jdk15u-dev/pull/181