RFR: 8338023: Support two vector selectFrom API [v15]

[Jatin Bhateja]

> Hi All,
> 
> As per the discussion on panama-dev mailing list[1], patch adds the support for following new two vector permutation APIs.
> 
> 
> Declaration:-
>     Vector<E>.selectFrom(Vector<E> v1, Vector<E> v2)
> 
> 
> Semantics:-
>     Using index values stored in the lanes of "this" vector, assemble the values stored in first (v1) and second (v2) vector arguments. Thus, first and second vector serves as a table, whose elements are selected based on index value vector. API is applicable to all integral and floating-point types.  The result of this operation is semantically equivalent to expression v1.rearrange(this.toShuffle(), v2). Values held in index vector lanes must lie within valid two vector index range [0, 2*VLEN) else an IndexOutOfBoundException is thrown.  
> 
> Summary of changes:
> -  Java side implementation of new selectFrom API.
> -  C2 compiler IR and inline expander changes.
> -  In absence of direct two vector permutation instruction in target ISA, a lowering transformation dismantles new IR into constituent IR supported by target platforms. 
> -  Optimized x86 backend implementation for AVX512 and legacy target.
> -  Function tests covering new API.
> 
> JMH micro included with this patch shows around 10-15x gain over existing rearrange API :-
> Test System: Intel(R) Xeon(R) Platinum 8480+ [ Sapphire Rapids Server]
> 
> 
>   Benchmark                                     (size)   Mode  Cnt      Score   Error   Units
> SelectFromBenchmark.rearrangeFromByteVector     1024  thrpt    2   2041.762          ops/ms
> SelectFromBenchmark.rearrangeFromByteVector     2048  thrpt    2   1028.550          ops/ms
> SelectFromBenchmark.rearrangeFromIntVector      1024  thrpt    2    962.605          ops/ms
> SelectFromBenchmark.rearrangeFromIntVector      2048  thrpt    2    479.004          ops/ms
> SelectFromBenchmark.rearrangeFromLongVector     1024  thrpt    2    359.758          ops/ms
> SelectFromBenchmark.rearrangeFromLongVector     2048  thrpt    2    178.192          ops/ms
> SelectFromBenchmark.rearrangeFromShortVector    1024  thrpt    2   1463.459          ops/ms
> SelectFromBenchmark.rearrangeFromShortVector    2048  thrpt    2    727.556          ops/ms
> SelectFromBenchmark.selectFromByteVector        1024  thrpt    2  33254.830          ops/ms
> SelectFromBenchmark.selectFromByteVector        2048  thrpt    2  17313.174          ops/ms
> SelectFromBenchmark.selectFromIntVector         1024  thrpt    2  10756.804          ops/ms
> SelectFromBenchmark.selectFromIntVector         2048  thrpt    2   5398.2...

Jatin Bhateja has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 18 commits:

 - Review comments resolution.
 - Merge branch 'master' of http://github.com/openjdk/jdk into JDK-8338023
 - Review comments resolutions.
 - Handling NPOT vector length for AArch64 SVE with vector sizes varying b/w 128 and 2048 bits at 128 bit increments.
 - Incorporating review and documentation suggestions.
 - Jcheck clearance
 - Review comments resolution.
 - Disabling VectorLoadShuffle bypassing optimization to comply with rearrange semantics at IR level.
 - Documentation suggestions from Paul.
 - Review resolutions.
 - ... and 8 more: https://git.openjdk.org/jdk/compare/bdfb41f9...6215ab91

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

Changes: https://git.openjdk.org/jdk/pull/20508/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20508&range=14
  Stats: 2804 lines in 89 files changed: 2785 ins; 18 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/20508.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20508/head:pull/20508

PR: https://git.openjdk.org/jdk/pull/20508