RFR: 8293488: Add EOR3 backend rule for aarch64 SHA3 extension

[Bhavana Kilambi]

Arm ISA v8.2A and v9.0A include SHA3 feature extensions and one of those SHA3 instructions - "eor3" performs an exclusive OR of three vectors. This is helpful in applications that have multiple, consecutive "eor" operations which can be reduced by clubbing them into fewer operations using the "eor3" instruction. For example -

eor a, a, b
eor a, a, c

can be optimized to single instruction - `eor3 a, b, c`

This patch adds backend rules for Neon and SVE2 "eor3" instructions and a micro benchmark to assess the performance gains with this patch. Following are the results of the included micro benchmark on a 128-bit aarch64 machine that supports Neon, SVE2 and SHA3 features -


Benchmark               gain
TestEor3.test1Int       10.87%
TestEor3.test1Long      8.84%
TestEor3.test2Int       21.68%
TestEor3.test2Long      21.04%


The numbers shown are performance gains with using Neon eor3 instruction over the master branch that uses multiple "eor" instructions instead. Similar gains can be observed with the SVE2 "eor3" version as well since the "eor3" instruction is unpredicated and the machine under test uses a maximum vector width of 128 bits which makes the SVE2 code generation very similar to the one with Neon.

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Commit messages:
 - 8293488: Add EOR3 backend rule for aarch64 SHA3 extension

Changes: https://git.openjdk.org/jdk/pull/10407/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10407&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8293488
  Stats: 345 lines in 10 files changed: 310 ins; 0 del; 35 mod
  Patch: https://git.openjdk.org/jdk/pull/10407.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10407/head:pull/10407

PR: https://git.openjdk.org/jdk/pull/10407