RFR: 8365991: AArch64: Ignore BlockZeroingLowLimit when UseBlockZeroing is false [v7]

[Patrick Zhang]

On Mon, 24 Nov 2025 09:13:19 GMT, Patrick Zhang <qpzhang at openjdk.org> wrote:

>> src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp line 6273:
>> 
>>> 6271:     result = zero_words(r10, r11);
>>> 6272:   } else {
>>> 6273: #ifndef PRODUCT
>> 
>> What is this change for?
>
> The reason of why I swapped the `if` and `else` code block is:
> 1). Initially, I intended to add a check for `UseBlockZeroing` to determine whether to call `zero_words_reg_reg`. Swapping the `if` and `else` branches makes it easier to compare the behavior with and without this additional condition. Otherwise, the if-cond would be like `if (!UseBlockZeroing || cnt <= (uint64_t)BlockZeroingLowLimit / BytesPerWord)`.
> 2). Later, we decided not to check `UseBlockZeroing` here but I still didn't roll back this change because the comments of warning `There is no need to check UseBlockZeroing..` should be placed before such an if condition, instead of the old one.

Resolved this if no further concern, thanks.

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PR Review Comment: https://git.openjdk.org/jdk/pull/26917#discussion_r2592467642