RFR: 8230486: G1BarrierSetAssembler::g1_write_barrier_post unnecessarily pushes/pops new_val [v2]

[Albert Mingkun Yang]

> Removes the unnecessary push/pop instruction.
> 
> Test: hotspot_gc

Albert Mingkun Yang has updated the pull request incrementally with one additional commit since the last revision:

  aarch64

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4063/files
  - new: https://git.openjdk.java.net/jdk/pull/4063/files/df025947..821a2650

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4063&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4063&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4063.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4063/head:pull/4063

PR: https://git.openjdk.java.net/jdk/pull/4063