[jdk17u-dev] RFR: 8265263: AArch64: Combine vneg with right shift count [v4]

[Dmitry Chuyko]

> This is a performance improvement for AArch64. There are several differences from the original change.
> 
> https://bugs.openjdk.org/browse/JDK-8267356 (Vector API SVE codegen support) is not in 17u, so `UseSVE == 0` parts in predicates are missing/excluded.
> 
> https://bugs.openjdk.org/browse/JDK-8288445 (C2 compilation fails) is a subsequent bugfix already backported in 17u, so some `immI` arguments in rules became `immI_positive`.
> 
> https://bugs.openjdk.org/browse/JDK-8277239 (SIGSEGV in vrshift_reg_maskedNode::emit) is also related to Vector API and is not in 17u, so `!n->as_ShiftV()->is_var_shift()` is replaced by `VectorNode::is_vshift_cnt(n->in(2))`. This substitution may raise doubts.
> 
> Testing: jtreg test/hotspot/jtreg/compiler, tier1, tier2 on aarch64.
> 
> Performance improvements in the added benchmark VectorShiftRight on Graviton 2 for default size=1024 correspond to the original review:
> 
> 
> rShiftByte      16%
> rShiftInt       27%
> rShiftLong      16%
> rShiftShort     20%
> urShiftByte     0%
> urShiftChar     20%
> urShiftInt      27%
> urShiftLong     16%

Dmitry Chuyko has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:

 - Merge branch 'openjdk:master' into JDK-8265263
 - Fixed m4 mismatch
 - No SVE checks in vsrcnt8B, vsrcnt16B
 - Backport 49245131e98c1c72c447536e5527acecb3311add

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

Changes:
  - all: https://git.openjdk.org/jdk17u-dev/pull/811/files
  - new: https://git.openjdk.org/jdk17u-dev/pull/811/files/0a9c5957..4d87503c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=811&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=811&range=02-03

  Stats: 3542 lines in 121 files changed: 2455 ins; 363 del; 724 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/811.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev pull/811/head:pull/811

PR: https://git.openjdk.org/jdk17u-dev/pull/811