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.

Just a few quick remarks.

src/hotspot/share/opto/vectornode.hpp line 188:

> 186: };
> 187: 
> 188: 

Suprious newline, please remove
Suggestion:

src/jdk.incubator.vector/share/classes/jdk/incubator/vector/VectorMathUtils.java line 78:

> 76:      * @since 24
> 77:      */
> 78:     public static long addSaturating(long a, long b) {

Are these public methods any Java dev could use? If so: do we have tests for them?

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

Changes requested by epeter (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/20507#pullrequestreview-2283248252
PR Review Comment: https://git.openjdk.org/jdk/pull/20507#discussion_r1745655940
PR Review Comment: https://git.openjdk.org/jdk/pull/20507#discussion_r1745665600