RFR: 8319872: AArch64: [vectorapi] Implementation of unsigned (zero extended) casts [v3]

[Eric Liu]

> Vector API defines zero-extend operations [1], which are going to be intrinsified and generated to `VectorUCastNode` by C2. This patch adds backend implementation for `VectorUCastNode` on AArch64.
> 
> The micro benchmark shows significant performance improvement. In my test machine (SVE, 256-bit), the result is shown as below:
> 
> 
> 
>   Benchmark                     Before     After       Units   Gain
>   VectorZeroExtend.byte2Int     3168.251   243012.399  ops/ms  75.70
>   VectorZeroExtend.byte2Long    3212.201   216291.588  ops/ms  66.33
>   VectorZeroExtend.byte2Short   3391.968   182655.365  ops/ms  52.85
>   VectorZeroExtend.int2Long     1012.197    80448.553  ops/ms  78.48
>   VectorZeroExtend.short2Int    1812.471   153416.828  ops/ms  83.65
>   VectorZeroExtend.short2Long   1788.382   129794.814  ops/ms  71.58
> 
> 
> On other Neon systems, we can get similar performance boost as a result of intrinsification success.
> 
> Since `VectorUCastNode` only used in Vector API's zero extension currently, this patch also adds assertion on nodes' definitions to clarify their usages.
> 
> [TEST]
> compiler/vectorapi and jdk/incubator/vector passed on NEON and SVE machines.
> 
> [1] https://github.com/openjdk/jdk/blob/master/src/jdk.incubator.vector/share/classes/jdk/incubator/vector/VectorOperators.java#L726

Eric Liu has updated the pull request incrementally with one additional commit since the last revision:

  add _sve_xunpk & remove dead code
  
  Change-Id: Ic19836feb8a73ea7e65443794f2a0eb1363f6e2f

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/16670/files
  - new: https://git.openjdk.org/jdk/pull/16670/files/4fb3128f..68748e7f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16670&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16670&range=01-02

  Stats: 85 lines in 2 files changed: 17 ins; 32 del; 36 mod
  Patch: https://git.openjdk.org/jdk/pull/16670.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16670/head:pull/16670

PR: https://git.openjdk.org/jdk/pull/16670