RFR: 8299323: Allow extended registers for cmpw

Fri Dec 23 12:48:50 UTC 2022

The current instruction encoder for cmpw(Address, int16_t) on x64 does not allow rex extended registers. Generational ZGC needs to use this for arbitrary registers. Let's add support for it instead of asserting the input Address uses a subset of registers.

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Commit messages:
 - 8299323: Allow extended registers for cmpw

Changes: https://git.openjdk.org/jdk/pull/11776/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11776&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8299323
  Stats: 3 lines in 1 file changed: 1 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/11776.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11776/head:pull/11776

PR: https://git.openjdk.org/jdk/pull/11776