[jdk11u-dev] RFR: 8292713: Unsafe.allocateInstance should be intrinsified without UseUnalignedAccesses [v2]

[Fei Yang]

> Backport to improve arm32 performance in 11u and riscv-port in: https://github.com/openjdk/riscv-port-jdk11u/pull/3.
> This is not a clean backport as the function has been moved to new file and renamed. 
> 
> I checked the 11u related code and I think the following analysis on the JBS description is still true for 11u:
> "The intrinsic is currently only implemented in C2. I see no reason for this intrinsic to depend on `UseUnalignedAccesses`: what `LibraryCallKit::inline_unsafe_allocate()` does seems similar to what the regular `Parse::do_new()` does, namely doing the clinit barrier and then delegating into `GraphKit::new_instance`."
> 
> Tested with the initial riscv-port in: https://github.com/openjdk/riscv-port-jdk11u/pull/3

Fei Yang 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 two additional commits since the last revision:

 - Merge remote-tracking branch 'upstream/master' into backport-8292713
 - 8292713: Unsafe.allocateInstance should be intrinsified without UseUnalignedAccesses

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

Changes:
  - all: https://git.openjdk.org/jdk11u-dev/pull/2125/files
  - new: https://git.openjdk.org/jdk11u-dev/pull/2125/files/22895ae1..719596c5

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2125&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2125&range=00-01

  Stats: 110 lines in 13 files changed: 38 ins; 25 del; 47 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2125.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2125/head:pull/2125

PR: https://git.openjdk.org/jdk11u-dev/pull/2125