RFR: 8343689: AArch64: Optimize MulReduction implementation [v12]

[Mikhail Ablakatov]

> Add a reduce_mul intrinsic SVE specialization for >= 256-bit long vectors. It multiplies halves of the source vector using SVE instructions to get to a 128-bit long vector that fits into a SIMD&FP register. After that point, existing ASIMD implementation is used.
> 
> Nothing changes for <= 128-bit long vectors as for those the existing ASIMD implementation is used directly still.
> 
> The benchmarks below are from [panama-vector/vectorIntrinsics:test/micro/org/openjdk/bench/jdk/incubator/vector/operation](https://github.com/openjdk/panama-vector/tree/vectorIntrinsics/test/micro/org/openjdk/bench/jdk/incubator/vector/operation). To the best of my knowledge, openjdk/jdk is missing VectorAPI reducion micro-benchmarks.
> 
> Benchmarks results:
> 
> Neoverse-V1 (SVE 256-bit)
> 
>   Benchmark                 (size)   Mode   master         PR  Units
>   ByteMaxVector.MULLanes      1024  thrpt 5447.643  11455.535 ops/ms
>   ShortMaxVector.MULLanes     1024  thrpt 3388.183   7144.301 ops/ms
>   IntMaxVector.MULLanes       1024  thrpt 3010.974   4911.485 ops/ms
>   LongMaxVector.MULLanes      1024  thrpt 1539.137   2562.835 ops/ms
>   FloatMaxVector.MULLanes     1024  thrpt 1355.551   4158.128 ops/ms
>   DoubleMaxVector.MULLanes    1024  thrpt 1715.854   3284.189 ops/ms
> 
> 
> Fujitsu A64FX (SVE 512-bit):
> 
>   Benchmark                 (size)   Mode   master         PR  Units
>   ByteMaxVector.MULLanes      1024  thrpt 1091.692   2887.798 ops/ms
>   ShortMaxVector.MULLanes     1024  thrpt  597.008   1863.338 ops/ms
>   IntMaxVector.MULLanes       1024  thrpt  510.642   1348.651 ops/ms
>   LongMaxVector.MULLanes      1024  thrpt  468.878    878.620 ops/ms
>   FloatMaxVector.MULLanes     1024  thrpt  376.284   2237.564 ops/ms
>   DoubleMaxVector.MULLanes    1024  thrpt  431.343   1646.792 ops/ms

Mikhail Ablakatov has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 23 commits:

 - cleanup: remove redundand local variables
   
   Change-Id: I6fb6a9a7a236537612caa5d53c5516ed2f260bad
 - cleanup: remove a trivial switch-case statement
   
   Change-Id: Ib914ce02ae9d88057cb0b88d4880df6ca64f8184
 - Assert the exact supported VL of 32B in SVE-specific methods
   
   Change-Id: I8768c653ff563cd8a7a75cd06a6523a9526d15ec
 - cleanup: fix long line formatting
   
   Change-Id: I173e70a2fa9a45f56fe50d4a6b81699665e3433d
 - fixup: remove VL asserts in match rules to fix failures on >= 512b SVE platforms
   
   Change-Id: I721f5a97076d645905ee1716f7d57ec8c90ef6e9
 - Merge branch 'master' into 8343689
   
   Change-Id: Iebe758e4c7b3ab0de5f580199f8909e96b8c6274
 - cleanup: start the SVE Integer Misc - Unpredicated section
 - Merge branch 'master'
 - Address review comments and simplify the implementation
   
   - remove the loops from gt128b methods making them 256b only
   - fixup: missed fnoregs in instruct reduce_mulL_256b
   - use an extra vtmp3 reg for the 256b integer method
   - remove a no longer needed change in reduce_mul_integral_le128b
   - cleanup: unify comments
 - Merge commit '8193856af8546332bfa180cb45154a4093b4fd2c'
 - ... and 13 more: https://git.openjdk.org/jdk/compare/cc563c87...8c9e0845

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

Changes: https://git.openjdk.org/jdk/pull/23181/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23181&range=11
  Stats: 274 lines in 6 files changed: 207 ins; 2 del; 65 mod
  Patch: https://git.openjdk.org/jdk/pull/23181.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23181/head:pull/23181

PR: https://git.openjdk.org/jdk/pull/23181