RFR: 8370666: VectorAPI: Add clear comments for vector relative code in c2 [v3]

[Emanuel Peter]

On Fri, 16 Jan 2026 08:45:56 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> Xiaohong Gong has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Update comments in type.cpp
>
> src/hotspot/share/opto/vectornode.hpp line 1912:
> 
>> 1910: // Unsigned vector cast operations can only be used in Vector API unsigned
>> 1911: // extensions between integral types so far. E.g., extending byte to float
>> 1912: // is not supported now.
> 
> Actually, we could totally implement it for the Auto Vectorizer. It would be methods like `Byte.toUnsignedInt`.

I filed it here with an example:
[JDK-8375502](https://bugs.openjdk.org/browse/JDK-8375502) C2 SuperWord: implement unsigned casts

If anybody is interested in taking on this task, feel free to reassign it to yourself :)

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PR Review Comment: https://git.openjdk.org/jdk/pull/29130#discussion_r2697533321