RFR: 8342601: AArch64: Micro-optimize bit shift in copy_memory [v3]

[Chad Rakoczy]

> [JDK-8342601](https://bugs.openjdk.org/browse/JDK-8342601)
> 
> Fix minor inefficiency in `copy_memory` by adding check before doing bit shift to see if we are able to do a move instruction instead. Change is low risk because of the low complexity of the change
> 
> Ran array copy and tier 1 on aarch64 machine
> 
> Test summary
> ==============================
>    TEST                                              TOTAL  PASS  FAIL ERROR   
>    jtreg:test/hotspot/jtreg/compiler/arraycopy          49    49     0     0   
> ==============================
> 
> ==============================
> Test summary
> ==============================
>    TEST                                              TOTAL  PASS  FAIL ERROR   
>    jtreg:test/hotspot/jtreg:tier1                     2591  2591     0     0   
>    jtreg:test/jdk:tier1                               2436  2436     0     0   
>    jtreg:test/langtools:tier1                         4577  4577     0     0   
>    jtreg:test/jaxp:tier1                                 0     0     0     0   
>    jtreg:test/lib-test:tier1                            34    34     0     0   
> ==============================

Chad Rakoczy has updated the pull request incrementally with one additional commit since the last revision:

  Update check

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/21589/files
  - new: https://git.openjdk.org/jdk/pull/21589/files/efae62ef..461e2a53

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21589&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21589&range=01-02

  Stats: 3 lines in 1 file changed: 2 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/21589.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21589/head:pull/21589

PR: https://git.openjdk.org/jdk/pull/21589