RFR: [11u] AArch64: JDK-8216989: CardTableBarrierSetAssembler::gen_write_ref_array_post_barrier() does not check for zero length on AARCH64

[Andrew Dinn]

Could I please have a review for the following backport to jdk11u.

  webrev:   http://cr.openjdk.java.net/~adinn/8216989-jdk11u/webrev.00/
  original: http://hg.openjdk.java.net/jdk/jdk/rev/7816d989bf21

The original patch failed to apply cleanly for two reasons.

  An assert in the downstream card table implementation had been removed
upstream which caused a match failure for one set of changes. The
replaced code was otherwise no different.

  Upstream changes to shenandoahBarrierSetAssembler_aarch64.cpp and
shenandoahBarrierSetAssembler_aarch64.cpp are not needed as the
associated abstraction classes don't exist in jdk11u -- instead calls go
direct through to the underlying card table routines.

Testing:
tier1 tests pass as before.

regards,


Andrew Dinn
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