RFR: 8268229: Aarch64: Use Neon in intrinsics for String.equals

[Andrew Haley]

On Tue, 15 Jun 2021 03:54:18 GMT, Nick Gasson <ngasson at openjdk.org> wrote:

> With this change the size of the`string_equals` intrinsic increases by ~60% from 120 bytes to 196 bytes and this gets expanded at every `String.equals` call site. It looks good on a micro-benchmark but I wonder if on a larger program this improvement is outweighed by the negative effects of methods taking up more space in the icache.

That's an excellent point. 

> With this change the size of the`string_equals` intrinsic increases by ~60% from 120 bytes to 196 bytes and this gets expanded at every `String.equals` call site. It looks good on a micro-benchmark but I wonder if on a larger program this improvement is outweighed by the negative effects of methods taking up more space in the icache.

That's an excellent point. There's no need at all for the Neon part to be expanded inline: it could be a subroutine. We'd have to use fixed Neon registers at the call site.

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PR: https://git.openjdk.java.net/jdk/pull/4423