RFR: 8350177: C2 SuperWord: Integer.numberOfLeadingZeros, numberOfTrailingZeros, reverse and bitCount have input types wrongly turncated for byte and short [v6]

[Emanuel Peter]

On Wed, 25 Jun 2025 06:44:24 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> Jasmine Karthikeyan has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Add more nodes to the non-truncating list
>
> src/hotspot/share/opto/superword.cpp line 2600:
> 
>> 2598:   case Op_XorReductionV:
>> 2599:   case Op_MaxReductionV:
>> 2600:   case Op_MinReductionV:
> 
> Why do these vector nodes even end up here? Is that expected?

Additionallly, it may be good to say why each one operation here is not truncatable. We can also file a follow-up RFE here, to add more investigation. After all, this is a bug-fix and we don't want to work in it too long now.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25440#discussion_r2165931037