RFR: 8268231: Aarch64: Use ldp in intrinsics for String.compareTo [v4]

[Andrew Haley]

On Wed, 28 Jul 2021 08:25:08 GMT, Nick Gasson <ngasson at openjdk.org> wrote:

> I don't think we want to keep two copies of the compareTo intrinsic. If there are no cases where the LDP version is worse than the original version then we should just delete the old one and replace it with this.

I agree. The trouble is, what does "worse" mean? I'm looking at SDEN-1982442, Neoverse N2 errata, 2001293, and I see that LDP has to be slowed down on streaming workloads, which will affect this.

The trouble with this patch is that it (probably) makes things better for long strings, which are very rare. What we actually need to care about is performance for a large number of typical-sized strings, which are names, identifiers, passwords, and so on: about 10-30 characters.

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PR: https://git.openjdk.java.net/jdk/pull/4722