RFR: 8294186: AArch64: VectorMaskToLong failed on SVE2 machine with -XX:UseSVE=1 [v2]

[Eric Liu]

> C2_MacroAssembler::sve_vmask_tolong would fail on BITPERM supported SVE2 machine with "-XX:UseSVE=1".
> 
> `BITPERM` is an optional feature in SVE2. With this feature, VectorMaskToLong has a more efficent implementation. For other cases, it should generate SVE1 code.
> 
> [TEST]
> jdk/incubator/vector, hotspot/compiler/vectorapi passed on BITPERM supported SVE2 machine, with option -XX:UseSVE=(0, 1, 2).

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

  Refine comment
  
  Change-Id: I785817a0068098e9c48221cb391ef776186ef5de

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/10443/files
  - new: https://git.openjdk.org/jdk/pull/10443/files/d8c3417e..6076974d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10443&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10443&range=00-01

  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/10443.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10443/head:pull/10443

PR: https://git.openjdk.org/jdk/pull/10443