RFR: 8277426: Optimize mask reduction operations on x86 [v2]

[Mai Đặng Quân Anh]

> Hi,
> 
> This patch improves the performance of mask reduction operations on AVX by matching the pattern `VectorMaskReduction (VectorStoreMask mask)` to eliminate the extra `VectorStoreMaskNode`. I have also done some refactoring to unify the logic of `toLong` with the other reduction operations.
> 
> The patch has been discussed partially in [panama-vector repository](https://github.com/openjdk/panama-vector/pull/158).
> 
> Passed all tests except the one being fixed by [JDK-8277324](https://bugs.openjdk.java.net/browse/JDK-8277324).
> 
> Thank you very much.

Mai Đặng Quân Anh 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:

 - Merge branch 'master' into vectorMaskReduction
 - reduce some dependencies with spare register
 - improve mask reduction logic on AVX

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6447/files
  - new: https://git.openjdk.java.net/jdk/pull/6447/files/d29b7ba0..1dae02d4

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6447&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6447&range=00-01

  Stats: 3137 lines in 166 files changed: 2359 ins; 150 del; 628 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6447.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6447/head:pull/6447

PR: https://git.openjdk.java.net/jdk/pull/6447