[jdk11u-dev] RFR: 8242449: AArch64: r27 can be allocated in CompressedOops mode

[Dmitry Chuyko]

This optimization saves a register in compressed oops mode. It requires JDK-8233743 as a prerequisite and JDK-8249781 as a post-fix. Original patch has been adjusted to use Universe::narrow_ptrs_base() instead of CompressedOops::ptrs_base() (no JDK-8223136) and for slightly different context (no JDK-8235385).

This PR is a combination JDK-8233743 + JDK-8242449.

Testing: tier1, tier2 (aarch64).

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Commit messages:
 - [PATCH] Backport f51088e261707d060ac1da11d44d6286fce0e46b
 - [PATCH] Backport e2644b70cfd7358d9c8cb22666c3a32876dcc8ff

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/137/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=137&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8242449
  Stats: 289 lines in 4 files changed: 73 ins; 174 del; 42 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/137.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/137/head:pull/137

PR: https://git.openjdk.java.net/jdk11u-dev/pull/137