RFR: 8255550: x86: Assembler::cmpq(Address dst, Register src) encoding is incorrect [v2]

[Aleksey Shipilev]

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

>> Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains two commits:
>> 
>>  - Merge branch 'master' into JDK-8255550-cmpq-incorrect
>>  - 8255550: x86: Assembler::cmpq(Address dst, Register src) encoding is incorrect
>
> 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.

Dropped the `safepoint_poll` hunk after #924 integration. @fisk, this must be fine with you then?

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