RFR: 8284563: AArch64: bitperm feature detection for SVE2 on Linux [v2]

[Eric Liu]

> This patch adds BITPERM feature detection for SVE2 on Linux. BITPERM is
> an optional feature in SVE2 [1]. It enables 3 SVE2 instructions (BEXT,
> BDEP, BGRP). BEXT and BDEP map efficiently to some vector operations,
> e.g., the compress and expand functionalities [2] which are proposed in
> VectorAPI's 4th incubation [3]. Besides, to generate specific code based
> on different architecture features like x86, this patch exports
> VM_Version::supports_XXX() for all CPU features.  E.g.,
> VM_Version::supports_svebitperm() for easy use.
> 
> This patch also fixes a trivial bug, that sets UseSVE back to 1 if it's
> 2 in SVE1 system.
> 
> [1] https://developer.arm.com/documentation/ddi0601/2022-03/AArch64-Registers/ID-AA64ZFR0-EL1--SVE-Feature-ID-register-0
> [2] https://bugs.openjdk.java.net/browse/JDK-8283893
> [3] https://bugs.openjdk.java.net/browse/JDK-8280173

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

  small fix
  
  Change-Id: Ida979f925055761ad73e50655d0584dcee24aea4

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8258/files
  - new: https://git.openjdk.java.net/jdk/pull/8258/files/1cfec16e..70fa72a0

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8258&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8258&range=00-01

  Stats: 8 lines in 3 files changed: 0 ins; 0 del; 8 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8258.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8258/head:pull/8258

PR: https://git.openjdk.java.net/jdk/pull/8258