RFR: 8338021: Support saturating vector operators in VectorAPI [v7]

[Emanuel Peter]

On Thu, 5 Sep 2024 08:34:36 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

>> Hi All,
>> 
>> As per the discussion on panama-dev mailing list[1], patch adds the support following new vector operators.
>> 
>> 
>>      . SUADD   : Saturating unsigned addition.
>>      . SADD    : Saturating signed addition. 
>>      . SUSUB   : Saturating unsigned subtraction.
>>      . SSUB    : Saturating signed subtraction.
>>      . UMAX    : Unsigned max
>>      . UMIN    : Unsigned min.
>>      
>> 
>> New vector operators are applicable to only integral types since their values wraparound in over/underflowing scenarios after setting appropriate status flags. For floating point types, as per IEEE 754 specs there are multiple schemes to handler underflow, one of them is gradual underflow which transitions the value to subnormal range. Similarly, overflow implicitly saturates the floating-point value to an Infinite value.
>> 
>> As the name suggests, these are saturating operations, i.e. the result of the computation is strictly capped by lower and upper bounds of the result type and is not wrapped around in underflowing or overflowing scenarios.
>> 
>> Summary of changes:
>> - Java side implementation of new vector operators.
>> - Add new scalar saturating APIs for each of the above saturating vector operator in corresponding primitive box classes, fallback implementation of vector operators is based over it.
>> - C2 compiler IR and inline expander changes.
>> - Optimized x86 backend implementation for new vector operators and their predicated counterparts.
>> - Extends existing VectorAPI Jtreg test suite to cover new operations.
>> 
>> Kindly review and share your feedback.
>> 
>> Best Regards,
>> PS: Intrinsification and auto-vectorization of new core-lib API will be addressed separately in a follow-up patch.
>> 
>> [1] https://mail.openjdk.org/pipermail/panama-dev/2024-May/020408.html
>
> Jatin Bhateja has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Some cleanups.

No time to review now. But the title only talks about saturating vector operations. UMin/ UMax is not really a saturating operation, right? Preferably, move it to a separate PR, or at least change the title, please :)

Just note on the length of this PR: people are not really excited to review 9k lines at once. I personally spend quite a bit of effort splitting things into smaller units, so that I get things reviewed quicker, and so that I make the life of the reviewer easier. It would be nice if you could split things into smaller units, I think in the end you would get more reviews quicker, and the result would be of higher quality.

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

PR Comment: https://git.openjdk.org/jdk/pull/20507#issuecomment-2331828999