RFR: 8299323: Allow extended registers for cmpw

[Erik Österlund]

On Fri, 23 Dec 2022 12:41:03 GMT, Erik Österlund <eosterlund at openjdk.org> wrote:

> 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.

Any takers?

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