RFR: 8326135: Enhance adlc to report unused operands [v2]

[kuaiwei]

On Wed, 21 Feb 2024 06:26:39 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> For example, stackSlotP in aarch64 is not used. If not do_form_by_name, it will be reported as unused.
>
> Got it. Please, add comment describing this special case for vector and stack operators.

Thanks for suggestion. I added the example in comments.

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PR Review Comment: https://git.openjdk.org/jdk/pull/17910#discussion_r1497083189