RFR: 8352585: Add special case handling for Float16.max/min x86 backend [v6]

[Sandhya Viswanathan]

On Fri, 28 Mar 2025 04:50:07 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

>> This bugfix patch adds the special handling as per x86 AVX512-FP16 ISA specification[1][2] to compute max/min operations with +/-0.0 or NaN operands.
>> 
>> Special handling leverage the instruction semantic, central idea is to shuffle the operands such that smaller input gets assigned to second operand for min operation or a larger input gets assigned to second operand for max operation, in addition result equals NaN if an unordered comparison detects first input as a NaN value else we return the result of min/max operation. 
>> 
>> Kindly review and share your feedback.
>> 
>> Best Regards,
>> Jatin
>> 
>> [1] https://www.felixcloutier.com/x86/vminsh
>> [2] https://www.felixcloutier.com/x86/vmaxsh
>
> Jatin Bhateja has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Adding custom NaN generator

test/hotspot/jtreg/compiler/intrinsics/float16/TestFloat16MaxMinSpecialValues.java line 58:

> 56:         if (Float16.isNaN(actual) && Float16.isNaN(expected)) {
> 57:             return false;
> 58:         }

This should be:
        if (Float16.isNaN(actual) ^ Float16.isNaN(expected)) {
            return true;
        }

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

PR Review Comment: https://git.openjdk.org/jdk/pull/24169#discussion_r2019389243