RFR: 8255550: x86: Assembler::cmpq(Address dst, Register src) encoding is incorrect

[Aleksey Shipilev]

On Thu, 29 Oct 2020 07:28:29 GMT, Erik Österlund <eosterlund at openjdk.org> wrote:

> Thanks for poking me. I would prefer to change to the cmpq instruction that has the opposite order in the stack watermark barrier instead. Everywhere in the code I talk about the condition being sp being "above" watermark. Changing it to less makes me twist my head in ways that heads should not twist.

Ok, so let's do this: can you change the parameter order in `cmpq` instruction in `safepoint_poll`, run the tests you probably know are sensitive to this, and I'll drop the `safepoint_poll` hunk from here after that change lands?

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PR: https://git.openjdk.java.net/jdk/pull/910