RFR: 8256438: AArch64: Implement match rules with ROR shift register value

[Eric Liu]

On Thu, 28 Jan 2021 14:26:32 GMT, Andrew Haley <aph at openjdk.org> wrote:

>> This patch transforms '(x >>> rshift) + (x << lshift)' into
>> 'RotateRight(x, rshift)' during GVN phase when both the shift exponents
>> are constants and their sum equals to the number of bits for the type
>> of shift base.
>> 
>> This patch implements some new match rules for AArch64 instructions
>> which can take ROR as the optional shift. Such instructions are 'and',
>> 'or', 'eor', 'eon', 'bic' and 'orn'.
>> 
>>   ror     w11, w2, #5
>>   eor     w0, w1, w11
>> 
>> With this patch, above code could be optimized to below:
>> 
>>   eor     w0, w1, w2, ror #5
>> 
>> Finally, the patch refactors TestRotate.java[1][2].
>> 
>> Tested jtreg TestRotate.java, hotspot::hotspot_all_no_apps,
>> jdk::jdk_core, langtools::tier1.
>> 
>> [1] https://bugs.openjdk.java.net/browse/JDK-8252776
>> [2] https://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2020-September/039911.html
>
> All that remains to do is the benchmarks.

I benchmarked on 7 platforms with jmh test[1], most of them were hard to see any performance changes. On one platform the performance become bad, and seems a little unstable.

Before:
Benchmark                Mode  Cnt    Score   Error  Units
Rotation.addRotateRight  avgt   15  270.080 ± 0.630  ns/op
Rotation.andRotateRight  avgt   15  269.000 ± 0.226  ns/op
Rotation.bicRotateRight  avgt   15  269.269 ± 0.769  ns/op
Rotation.eonRotateRight  avgt   15  269.456 ± 0.056  ns/op
Rotation.ornRotateRight  avgt   15  269.681 ± 1.028  ns/op
Rotation.xorRotateRight  avgt   15  270.953 ± 2.764  ns/op
After:
Benchmark                Mode  Cnt    Score    Error  Units
Rotation.addRotateRight  avgt   15  399.995 ± 10.702  ns/op
Rotation.andRotateRight  avgt   15  399.517 ±  7.933  ns/op
Rotation.bicRotateRight  avgt   15  396.602 ±  2.038  ns/op
Rotation.eonRotateRight  avgt   15  401.978 ± 17.371  ns/op
Rotation.ornRotateRight  avgt   15  431.052 ± 73.711  ns/op
Rotation.xorRotateRight  avgt   15  410.447 ± 42.929  ns/op
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[1] http://cr.openjdk.java.net/~xgong/rfr/8256438/Rotation.java

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PR: https://git.openjdk.java.net/jdk/pull/1858