RFR: 8262989: Vectorize VectorShuffle checkIndexes, wrapIndexes and laneIsValid methods

[Sandhya Viswanathan]

On Thu, 4 Mar 2021 16:47:30 GMT, Paul Sandoz <psandoz at openjdk.org> wrote:

>> The hot path of VectorShuffle checkIndexes, wrapIndexes and laneIsValid methods can be implemented using Vector API methods.
>> 
>> For the attached jmh TestSlice.java, performance improves as below.
>> 
>> Before: 
>> Benchmark                                     (size)   Mode  Cnt     Score    Error   Units
>> TestSlice.vectorSliceOrigin                     1024  thrpt    5  1224.698 ± 53.825  ops/ms
>> TestSlice.vectorSliceUnsliceOrigin              1024  thrpt    5   657.895 ± 31.945  ops/ms
>> 
>> After: 
>> Benchmark                                     (size)   Mode  Cnt      Score    Error   Units
>> TestSlice.vectorSliceOrigin                     1024  thrpt    5  11221.532 ± 88.616  ops/ms
>> TestSlice.vectorSliceUnsliceOrigin              1024  thrpt    5   6509.519 ± 18.102  ops/ms
>
> Looks good, a nice incremental improvement.
> 
> I suppose `checkIndexes` and `wrapIndexes` could call `laneIsValid`, and then call `anyFalse` on the resulting mask. Dunno if that would affect the generated code.

Calling laneIsValid from checkIndexes and wrapIndexes would look like as below:
        VectorMask<E> vecmask = this.laneIsValid();
        if (!vecmask.allTrue()) {
I observe a small overhead (~2%) due to couple of extra instructions generated for allTrue.

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PR: https://git.openjdk.java.net/jdk/pull/2819