RFR: 8293409: [vectorapi] Intrinsify VectorSupport.indexVector

[Vladimir Kozlov]

On Mon, 19 Sep 2022 08:51:24 GMT, Xiaohong Gong <xgong at openjdk.org> wrote:

> "`VectorSupport.indexVector()`" is used to compute a vector that contains the index values based on a given vector and a scale value (`i.e. index = vec + iota * scale`). This function is widely used in other APIs like "`VectorMask.indexInRange`" which is useful to the tail loop vectorization. And it can be easily implemented with the vector instructions.
> 
> This patch adds the vector intrinsic implementation of it. The steps are:
> 
>   1) Load the const "iota" vector.
> 
>   We extend the "`vector_iota_indices`" stubs from byte to other integral types. For floating point vectors, it needs an additional vector cast to get the right iota values.
> 
>   2) Compute indexes with "`vec + iota * scale`"
> 
> Here is the performance result to the new added micro benchmark on ARM NEON:
> 
> Benchmark                              Gain
> IndexVectorBenchmark.byteIndexVector   1.477
> IndexVectorBenchmark.doubleIndexVector 5.031
> IndexVectorBenchmark.floatIndexVector  5.342
> IndexVectorBenchmark.intIndexVector    5.529
> IndexVectorBenchmark.longIndexVector   3.177
> IndexVectorBenchmark.shortIndexVector  5.841
> 
> 
> Please help to review and share the feedback! Thanks in advance!

@jatin-bhateja and @sviswa7 please look on this enhancement as Vector API experts.

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

PR: https://git.openjdk.org/jdk/pull/10332