RFR: 8297753: AArch64: Add optimized rules for vector compare with zero on NEON [v6]

[Chang Peng]

> We can use the compare-with-zero instructions like cmgt(zero)[1] immediately to avoid the extra scalar2vector operations.
> 
> The following instruction sequence
> 
> movi  v16.4s, #0x0
> cmgt  v16.4s, v17.4s, v16.4s
> 
> can be optimized to:
> 
> cmgt v16.4s, v17.4s, #0x0
> 
> This patch does the following:
> 1. Add NEON floating-point compare-with-zero instructions.
> 2. Add optimized match rules to generate the compare-with-zero instructions.
> 
> [1]: https://developer.arm.com/documentation/ddi0602/2022-06/SIMD-FP-Instructions/CMGT--zero---Compare-signed-Greater-than-zero--vector--

Chang Peng has updated the pull request incrementally with two additional commits since the last revision:

 - Remove some switch-case stmts in c2_MacroAssembler_aarch64.cpp and avoid
   unsigned comparison.
 - Revert "Remove switch-case stmts in c2_MacroAssembler_aarch64.cpp"
   
   This reverts commit d899238d0cb98fdf375b3011670495c3bfe8bbaf.

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/11822/files
  - new: https://git.openjdk.org/jdk/pull/11822/files/3e46cb2b..2431d1e4

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11822&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11822&range=04-05

  Stats: 30 lines in 2 files changed: 25 ins; 5 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/11822.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11822/head:pull/11822

PR: https://git.openjdk.org/jdk/pull/11822