RFR: 8241502: Migrate x86_64.ad to MacroAssembler

[Dean Long]

On Sat, 6 Mar 2021 00:53:44 GMT, John Tortugo <github.com+2249648+JohnTortugo at openjdk.org> wrote:

>> @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!
>
> Hi again, here is a quick update on the progress of this and an ask for advice.
> 
> I finished doing all conversions. I'm using an automated approach to validate the conversions: for each instruction that I converted I created an `enc_class` (just for debugging purposes) with pretty much the code that @dean-long provided above. However, I'm hitting a limitation on test coverage. I performed 248 conversions, but until now I was able to test only 203! I've tested tier1, tier2, and tier3 with different GCs, different VM options, on Linux and macOS. In other words, I've tried several things that I could think of but I couldn't make C2 use some instructions. 
> 
> I created a [Gist with the list of instructions I couldn't test so far](https://gist.github.com/JohnTortugo/c6d09a8ef6160422d6bf0ae5f894c1fe). Can you suggest something I can do to make C2 use those additional instructions?

Was -Xcomp one of the flags you tried?  If so, then you may need to write new tests for those instructions without test coverage.  Or you could do the 203 first and file a new RFE for the remaining.

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