RFR: JDK-8310502 : Optimization for j.l.Long.fastUUID() [v22]

[Glavo]

On Mon, 26 Jun 2023 14:40:08 GMT, Roger Riggs <rriggs at openjdk.org> wrote:

> The implementation should do its best whether or not CompactStrings is true or false. (Until the time it is deprecated and remove). Throwing an internal error is not an option.

I understand that we must provide a working implementation for it, but do we really need to do our best to optimize for it?

Take this PR as an example. By using `newStringNoRepl`, it has the best performance when `COMPACT_STRINGS` is `true` and can also work when `COMPACT_STRINGS` is `false`.

But if we want the best performance in both cases, then we will have to create another method to carefully optimize for situations where `COMPACT_STRINGS` is `false`.

What I want to know is whether it is necessary for us to do so? Or do we only need to focus on optimizing situations where `COMPACT_STRINGS` is `true`, while other situations do not require careful optimization?

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PR Comment: https://git.openjdk.org/jdk/pull/14578#issuecomment-1607664719