RFR: 8372978: [VectorAPI] Fix incorrect identity values in UMIN/UMAX reductions [v2]

[Eric Fang]

On Fri, 12 Dec 2025 08:42:22 GMT, Eric Fang <erfang at openjdk.org> wrote:

>> The original implementation of UMIN/UMAX reductions in JDK-8346174 used incorrect identity values in the Java implementation and test code.
>> 
>> Problem:
>> --------
>> UMIN was using MAX_OR_INF (signed maximum value) as the identity:
>>   - Byte.MAX_VALUE (127) instead of max unsigned byte (255)
>>   - Short.MAX_VALUE (32767) instead of max unsigned short (65535)
>>   - Integer.MAX_VALUE instead of max unsigned int (-1)
>>   - Long.MAX_VALUE instead of max unsigned long (-1)
>> 
>> UMAX was using MIN_OR_INF (signed minimum value) as the identity:
>>   - Byte.MIN_VALUE (-128) instead of 0
>>   - Short.MIN_VALUE (-32768) instead of 0
>>   - Integer.MIN_VALUE instead of 0
>>   - Long.MIN_VALUE instead of 0
>> 
>> This caused incorrect result. For example:
>>   UMAX([42,42,...,42]) returned 128 instead of 42
>> 
>> Solution:
>> ---------
>> Use correct unsigned identity values:
>>   - UMIN: ($type$)-1 (maximum unsigned value)
>>   - UMAX: ($type$)0 (minimum unsigned value)
>> 
>> Changes:
>> --------
>> - X-Vector.java.template: Fixed identity values in reductionOperations
>> - gen-template.sh: Fixed identity values for test code generation
>> - templates/Unit-header.template: Updated copyright year to 2025
>> - Regenerated all Vector classes and test files
>> 
>> Testing:
>> --------
>> All types (byte/short/int/long) now return correct results in both interpreter mode (-Xint) and compiled mode.
>
> Eric Fang has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:
> 
>  - Declare two constants for UMIN/UMAX reduction identity values
>  - Merge branch 'master' into JDK-8372978-fix-umin-umax-identity
>  - 8372978: [VectorAPI] Fix incorrect identity values in UMIN/UMAX reductions
>    
>    The original implementation of UMIN/UMAX reductions in JDK-8346174
>    used incorrect identity values in the Java implementation and test code.
>    
>    Problem:
>    --------
>    UMIN was using MAX_OR_INF (signed maximum value) as the identity:
>      - Byte.MAX_VALUE (127) instead of max unsigned byte (255)
>      - Short.MAX_VALUE (32767) instead of max unsigned short (65535)
>      - Integer.MAX_VALUE instead of max unsigned int (-1)
>      - Long.MAX_VALUE instead of max unsigned long (-1)
>    
>    UMAX was using MIN_OR_INF (signed minimum value) as the identity:
>      - Byte.MIN_VALUE (-128) instead of 0
>      - Short.MIN_VALUE (-32768) instead of 0
>      - Integer.MIN_VALUE instead of 0
>      - Long.MIN_VALUE instead of 0
>    
>    This caused incorrect result. For example:
>      UMAX([42,42,...,42]) returned 128 instead of 42
>    
>    Solution:
>    ---------
>    Use correct unsigned identity values:
>      - UMIN: ($type$)-1 (maximum unsigned value)
>      - UMAX: ($type$)0 (minimum unsigned value)
>    
>    Changes:
>    --------
>    - X-Vector.java.template: Fixed identity values in reductionOperations
>    - gen-template.sh: Fixed identity values for test code generation
>    - templates/Unit-header.template: Updated copyright year to 2025
>    - Regenerated all Vector classes and test files
>    
>    Testing:
>    --------
>    All types (byte/short/int/long) now return correct results in both
>    interpreter mode (-Xint) and compiled mode.

Since this issue https://bugs.openjdk.org/browse/JDK-8373390, I didn't merge the latest master branch into this PR. After that issue is fixed, I'll resolve the merge conflicts.

-------------

PR Comment: https://git.openjdk.org/jdk/pull/28692#issuecomment-3645539137