RFR: 8241502: Migrate x86_64.ad to MacroAssembler [v6]

[Vladimir Kozlov]

On Thu, 25 Mar 2021 17:09:07 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> John Tortugo has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   All conversions performed and tested.
>
> Marked as reviewed by kvn (Reviewer).

> > I guess you counted an instruction validated if it was generated at least once (so at least 1 possible encoding)? On RISC architectures that would probably be enough, but I know on x86/x64, register choice can change the instruction encoding and length, thanks to prefixes, etc.
> 
> One possibility is to write a native test (using gtest) and exercise some encoding methods by enumerating all the possible input value locations. Probably, too much for a regularly executed test (there's a lot of stuff missing right now to support such scenario), but something which can be quickly hacked for a one-time run.

I suggest to do that as separate RFE. This changes could be tested by running in all our tiers testing.

Cleaning unused code could be also done separately.

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PR: https://git.openjdk.java.net/jdk/pull/2420