RFR: 8268363: AArch64: Implement string_indexof_char intrinsic in SVE [v3]

[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 with a new target base due to a merge or a rebase. The pull request now contains one commit:

  8268363: AArch64: Implement string_indexof_char intrinsic in SVE
  
  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

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

Changes: https://git.openjdk.java.net/jdk/pull/4567/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4567&range=02
  Stats: 388 lines in 9 files changed: 269 ins; 0 del; 119 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