RFR: 8241502: Migrate x86_64.ad to MacroAssembler

[John Tortugo]

On Wed, 17 Feb 2021 09:47:13 GMT, Dean Long <dlong at openjdk.org> wrote:

>> Thank you all for the feedback!
>> 
>> @iklam - I'll check that and let you know once I make more conversions.
>> 
>> @dean-long - That would be great. I'm all ears for the best way to test this!
>
> Here's one way to test both versions, using loadRange as an example.  It's not exactly pretty, but it seems to work.
> [loadRange.txt](https://github.com/openjdk/jdk/files/5994725/loadRange.txt)

@dean-long - I recently hacked something pretty similar - basically, I added a flag to the CodeSection class to make it print emitted bytes whenever the flag was set, then I created two encoding classes in the AD file to toggle the print flag. That way I was able to _visually_ compare the output of the two versions of the code. Your approach with the CRC is much better. Thanks a lot!

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