RFR: 8268363: AArch64: Implement string_indexof_char intrinsic in SVE [v4]

[TatWai Chong]

> This patch implements string_indexof_char intrinsic in SVE for both
> UTF-16 and Latin-8 variants. In the current underneath implementation,
> there is only 4 and 8 characters are compared at a time in UTF-16 and
> Latin-8 respectively. In this patch, we adopt SVE to vectorize this
> intrinsic so that a wider comparison can be performed each time.
> 
> I've run [1] with this patch on an SVE machine, and the performance of
> StringIndexOfChar.latin1_mixed_char (length=65) and
> StringIndexOfChar.utf16_mixed_char (length=65) are improved significantly,
> while no visible regression for other cases with shorter strings.
> (length=7, 8, 15, 16 and 32)
> 
> [1] https://github.com/openjdk/jdk/blob/master/test/micro/org/openjdk/bench/java/lang/StringIndexOfChar.java

TatWai Chong has updated the pull request incrementally with one additional commit since the last revision:

  Merge these intrinsic instructs into a macro.

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4567/files
  - new: https://git.openjdk.java.net/jdk/pull/4567/files/72b1120d..4c6d0946

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4567&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4567&range=02-03

  Stats: 39 lines in 2 files changed: 7 ins; 14 del; 18 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4567.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4567/head:pull/4567

PR: https://git.openjdk.java.net/jdk/pull/4567