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List:       openjdk-hotspot-compiler-dev
Subject:    Re: RFR: 8276162: Optimise unsigned comparison pattern
From:       Mai =?UTF-8?B?xJDhurduZw==?= =?UTF-8?B?IA==?= =?UTF-8?B?UXXDom4=?= Anh <duke () ope
Date:       2021-10-29 9:48:34
Message-ID: 8mMToQfY2jwnP4ASypeTpEGcS_RK4c0tQnkUe4uy9dc=.febcbe8f-109b-460b-97b7-0c7f8df8f078 () github ! com
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On Mon, 25 Oct 2021 10:15:42 GMT, Mai Đặng Quân Anh <duke@openjdk.java.net> \
wrote:

> This patch changes operations in the form `x +- Integer.MIN_VALUE <=> y +- \
> Integer.MIN_VALUE`, which is a pattern used to do unsigned comparisons, into `x \
> u<=> y`. 
> In addition to being basic operations, they may be utilised to implement range \
> checks such as the methods in `jdk.internal.util.Preconditions`, or in places where \
> the compiler cannot deduce the non-negativeness of the bound as in \
> `java.util.ArrayList`. 
> Thank you very much.

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 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.

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

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


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