RFR: JDK-8300783: Consolidate byteswap implementations [v8]

[David Holmes]

On Tue, 24 Jan 2023 16:14:22 GMT, Justin King <jcking at openjdk.org> wrote:

>> Deduplicate byte swapping implementations by consolidating them into `utilities/byteswap.hpp`, following `std::byteswap` introduced in C++23. Further simplification of `Bytes` will follow in https://github.com/openjdk/jdk/pull/12078.
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> Justin King has updated the pull request incrementally with one additional commit since the last revision:
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>   Update comment
>   
>   Signed-off-by: Justin King <jcking at google.com>

Cleanup/consolidation looks really good. Have to wonder if we can go further with `get_Java_u2` etc, in a next step?

The actual byteswap stuff seems okay but not really my area and compiler specific actions are not something I'm at all familiar with.

I will grab this and run through our CI. Thanks.

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PR: https://git.openjdk.org/jdk/pull/12114