RFR: 8305959: x86: Improve itable_stub [v2]

[Boris Ulasevich]

On Tue, 23 May 2023 12:21:58 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> The performance improvements for the interface calls look impressive.
> 
> I have a major suggestion on readability, see [8305959-1.patch](https://github.com/openjdk/jdk/files/11543559/8305959-1.patch). It renames the labels, renames the loops, collects the comments together, etc. It passes `runtime/InvocationTests`, but I have not tested anything else.
> 
> How was this change tested, by the way?
> 
> Should this also be "x86: Improve itable_stub", seeing how this is x86-specific?

I totally agree with your change. It really looks much cleaner this way.
I checked that your changes are algebraically equivalent transformations, though I rerun jtreg hotspot+jdk tier1,2,3 tests.
I think this amount of testing is fine. These stubs are heavily used, and any small bug here would cause a ton of tests to fail.
And yes, I rename the PR.
Thank you very much!

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PR Comment: https://git.openjdk.org/jdk/pull/13460#issuecomment-1563978503