RFR: 8276162: Optimise unsigned comparison pattern

[Jie Fu]

On Fri, 29 Oct 2021 07:23:56 GMT, Mai Đặng Quân Anh <duke at openjdk.java.net> wrote:

> I created a simple benchmark, the benchmark is run on Intel i7-7700HQ, the result is as follow:
> 
> ```
> Before:
> Benchmark    Mode  Cnt  Score   Error  Units
> App.runInt   avgt   25  3.963 ± 0.181  ns/op
> App.runLong  avgt   25  4.431 ± 0.101  ns/op
> 
> After:
> Benchmark    Mode  Cnt  Score   Error  Units
> App.runInt   avgt   25  3.678 ± 0.192  ns/op
> App.runLong  avgt   25  3.814 ± 0.085  ns/op
> ```
> 
> This is the source code of the benchmark:
> 
> ```
> package io.github.merykitty.simplebenchmark;
> 
> import java.io.IOException;
> import java.util.concurrent.TimeUnit;
> 
> import org.openjdk.jmh.annotations.*;
> import org.openjdk.jmh.infra.Blackhole;
> 
> @BenchmarkMode(Mode.AverageTime)
> @State(Scope.Benchmark)
> @OutputTimeUnit(TimeUnit.NANOSECONDS)
> @Warmup(iterations = 5)
> @Measurement(iterations = 5)
> public class App {
>     @CompilerControl(CompilerControl.Mode.DONT_INLINE)
>     public long test(int arg0, int arg1) {
>         return arg0 + Integer.MIN_VALUE < arg1 + Integer.MIN_VALUE ? 1 : 0;
>     }
> 
>     @CompilerControl(CompilerControl.Mode.DONT_INLINE)
>     public long test(long arg0, long arg1) {
>         return arg0 + Long.MIN_VALUE < arg1 + Long.MIN_VALUE ? 1 : 0;
>     }
> 
>     @Benchmark
>     public void runInt() {
>         test(0, -1);
>         test(-1, 0);
>     }
> 
>     @Benchmark
>     public void runLong() {
>         test(0L, -1L);
>         test(-1L, 0L);
>     }
> 
>     public static void main( String[] args ) throws IOException {
>         org.openjdk.jmh.Main.main(args);
>     }
> }
> ```
> 
> Do I need to add the benchmark to the patch? If yes then where should I put it in?
> 
> Thank you very much.

I think you can put it under `test/micro/org/openjdk/bench/vm/compiler` with a more meaningful class name.
Please note that the jcheck failed in your PR, which seems to prevent the RFR email from sending out.

> I have just pushed the microbenchmark, I am not sure what to put in the copyright line, though.
> 
> The check failure seems to be due to this PR does not refer to an existing issue.
> 
> Thank you very much.

Filed https://bugs.openjdk.java.net/browse/JDK-8276162 for you.
Thanks.

-------------

PR: https://git.openjdk.java.net/jdk/pull/6101