[jdk18] RFR: 8274243: Implement fast-path for ASCII-compatible CharsetEncoders on aarch64

[Andrew Haley]

On Wed, 15 Dec 2021 15:07:41 GMT, Patric Hedlin <phedlin at openjdk.org> wrote:

> > We're in RDP1 since December 9. This means that any enhancement is covered by the Late-Enhancement Request Process. https://openjdk.java.net/jeps/3#Late-Enhancement-Request-Process . I don't think this patch is urgent enough for that.
> 
> It has been classified as a performance regression (bug) in line with the x86 issue (JDK-8274242). Do you mean we should change this _now_? Aarch64 would be the only platform not to address the issue in JDK-18.

I see your point, and that is a significant difference. It's unfortunate that AArch64 got this patch late in the process, but as it's a bug, and Java performance isn't supposed to regress in a release, it does make sense to fix it. Having said that, I've had a lot of bad experiences with late patches, and it'd be a dreadful shame if we broke AArch64 string handling.

I suppose the best way to proceed with this is to have two AArch64 reviewers go through the patch instruction by instruction, just to make sure the test covers all corner cases. Thanks.

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PR: https://git.openjdk.java.net/jdk18/pull/20