RFR: 8372978: [VectorAPI] Fix incorrect identity values in UMIN/UMAX reductions [v4]

[Paul Sandoz]

On Fri, 19 Dec 2025 09:55:25 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 incrementally with one additional commit since the last revision:
> 
>   Refine the tests for identity values

Very good, a good stepping stone to for further improvements to declare and test these constants. Just one last comment which i hope will be easy to address then I think its good for integration.

test/jdk/jdk/incubator/vector/templates/Unit-Reduction-op-func.template line 25:

> 23:                                 "[[TEST]](" + x + ", [[TEST_INIT]]) != " + x);
> 24:         }
> 25:     }

Just one last thing wrap the loop in a `try/catch(AssertionError e)` where the `assertEquals` in the loop do not pass in a string argument. The production of such strings within the loop slow the tests down. In the catch duplicate the `assertEquals with the string argument.

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

PR Review: https://git.openjdk.org/jdk/pull/28692#pullrequestreview-3600300548
PR Review Comment: https://git.openjdk.org/jdk/pull/28692#discussion_r2636437477