RFR: 8354242: VectorAPI: combine vector not operation with compare [v9]

[erifan]

On Tue, 8 Jul 2025 11:42:18 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> Oh wow, my bad. I misunderstood the brackets!
>> 
>> Instead of:
>> 
>>       !(in1->as_VectorMaskCmp())->predicate_can_be_negated() ||
>>       !VectorNode::is_all_ones_vector(in2)) {
>> 
>> I read:
>> 
>>       !(in1->as_VectorMaskCmp()->predicate_can_be_negated() ||
>>       !VectorNode::is_all_ones_vector(in2))) {
>> 
>> That confused me a lot... absolutely my bad.
>> 
>> Well actually then my indentation suggestion was terrible!
>
> I made a new suggestion below.

> A code comment would be helpful for this case. 

I updated the comment above the code a bit. As for why predicate need to be negatable, it's straightforward, the key of this optimization is to change predicate condition into negative predicate condition. And in `predicate_can_be_negated`, there's a comment explaining when predicate can't be negated.

> I made a new suggestion below.

Done.

> That confused me a lot... absolutely my bad.
Well actually then my indentation suggestion was terrible!

No problem. I'm a newbie in the JDK community, so generally I think your suggestions are valuable.Thanks for your review!

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PR Review Comment: https://git.openjdk.org/jdk/pull/24674#discussion_r2194130234