RFR: 8365991: AArch64: Ignore BlockZeroingLowLimit when UseBlockZeroing is false [v4]

[Patrick Zhang]

On Tue, 28 Oct 2025 12:08:01 GMT, Andrew Haley <aph at openjdk.org> wrote:

> That is to say, if a user sets `BlockZeroingLowLimit` and `-XX:-UseBlockZeroing`, then the user's `BlockZeroingLowLimit` is, rightly, ignored.

Yes, this is the current state we have, with the patch, and it also represents the compromise I can accept regarding `zero_words` using `BlockZeroingLowLimit` to decide between "unroll vs callout" without checking `UseBlockZeroing`. I added necessary [comments](https://github.com/openjdk/jdk/pull/26917/files#diff-0f4150a9c607ccd590bf256daa800c0276144682a92bc6bdced5e8bc1bb81f3aR6264-R6268) to warn others from having similar confusion or misunderstanding about this code snippet.

Is there anything else we need to do for this PR?

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PR Comment: https://git.openjdk.org/jdk/pull/26917#issuecomment-3462054378