RFR: 8277617: Optimize array copy and clear on x86_64

[Sandhya Viswanathan]

Currently 32-byte instructions are used for small array copy and clear. 
This can be optimized by using 64-byte instructions.

Please review.

Best Regards,
Sandhya

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Commit messages:
 - 8277617: Optimize array copy and clear on x86_64

Changes: https://git.openjdk.java.net/jdk/pull/6512/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6512&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8277617
  Stats: 15 lines in 4 files changed: 2 ins; 0 del; 13 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6512.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6512/head:pull/6512

PR: https://git.openjdk.java.net/jdk/pull/6512