RFR: 8338021: Support saturating vector operators in VectorAPI [v5]

[Emanuel Peter]

On Mon, 2 Sep 2024 12:20:59 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:
> 
>   Review comments resolved

Ok, I left a few more comments. I think this PR could definately be split. It would make it more reviewable for me.

src/hotspot/share/opto/vectornode.hpp line 148:

> 146: 
> 147: //===========================Vector=ALU=Operations=============================
> 148: class SaturatingVectorNode : public VectorNode {

Semantics description of Saturation would be appreciated :)

src/hotspot/share/opto/vectornode.hpp line 634:

> 632:   virtual int Opcode() const;
> 633: };
> 634: 

This could also be a separate PR. Or are they somehow inseparable from the "saturation" changes?

src/hotspot/share/prims/vectorSupport.hpp line 129:

> 127:     VECTOR_OP_SUSUB = 122,
> 128:     VECTOR_OP_UMIN = 123,
> 129:     VECTOR_OP_UMAX = 124,

Please keep the alignment consistent.

src/java.base/share/classes/java/lang/Integer.java line 1994:

> 1992:      * @return the greater of {@code a} and {@code b}
> 1993:      * @see java.util.function.BinaryOperator
> 1994:      * @since 1.8

Is this a copy error or did this already exist since `1.8`?

src/java.base/share/classes/jdk/internal/vm/vector/VectorSupport.java line 395:

> 393: 
> 394:     /* ============================================================================ */
> 395: 

These comment lines seem redundant...

test/jdk/jdk/incubator/vector/gen-template.sh line 317:

> 315: function gen_saturating_binary_op {
> 316:   echo "Generating binary op $1 ($2)..."
> 317: #  gen_op_tmpl $binary_scalar "$@"

Is this commented on purpose?

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

Changes requested by epeter (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/20507#pullrequestreview-2277361678
PR Review Comment: https://git.openjdk.org/jdk/pull/20507#discussion_r1742016482
PR Review Comment: https://git.openjdk.org/jdk/pull/20507#discussion_r1742019985
PR Review Comment: https://git.openjdk.org/jdk/pull/20507#discussion_r1742021810
PR Review Comment: https://git.openjdk.org/jdk/pull/20507#discussion_r1742024534
PR Review Comment: https://git.openjdk.org/jdk/pull/20507#discussion_r1742026062
PR Review Comment: https://git.openjdk.org/jdk/pull/20507#discussion_r1742028394