RFR: 8271579: G1: Move copy before CAS in do_copy_to_survivor_space [v4]

[Hamlin Li]

> Propose to move copy before CAS in do_copy_to_survivor_space, as we found this will improve G1 performance. Specjbb shows 3.7% in critical on aarch64, no change in max.
> 
> After this change copy_to_survivor in G1 is also aligned with PS's copy_to_survivor.

Hamlin Li has updated the pull request incrementally with one additional commit since the last revision:

  Closes JDK-8272070: simplify age calculation

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4983/files
  - new: https://git.openjdk.java.net/jdk/pull/4983/files/997fdc19..a3ebe710

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4983&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4983&range=02-03

  Stats: 11 lines in 1 file changed: 0 ins; 10 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4983.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4983/head:pull/4983

PR: https://git.openjdk.java.net/jdk/pull/4983