RFR: 8293409: [vectorapi] Intrinsify VectorSupport.indexVector [v2]

[Xiaohong Gong]

> "`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!

Xiaohong Gong has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Add the floating point support for VectorLoadConst and remove the VectorCast
 - Merge branch 'master' into JDK-8293409
 - 8293409: [vectorapi] Intrinsify VectorSupport.indexVector

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/10332/files
  - new: https://git.openjdk.org/jdk/pull/10332/files/2ad157b6..53f042d3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10332&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10332&range=00-01

  Stats: 50675 lines in 1239 files changed: 30581 ins; 14395 del; 5699 mod
  Patch: https://git.openjdk.org/jdk/pull/10332.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10332/head:pull/10332

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