/*
 * Copyright (c) 2017, Red Hat Inc. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
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 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package org.openjdk.gcbench.runtime.cmp;

import org.openjdk.jmh.annotations.*;

import java.util.concurrent.TimeUnit;

@Warmup(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
@Measurement(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
@Fork(1)
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
@Threads(1)
@State(Scope.Thread)
public class ACmpBarriersKnownNulls {

    Object target;

    @Setup
    public void setup() {
        target = new Object();
    }

    @Benchmark
    public void left() {
        doLeft(target);
    }

    @Benchmark
    public void right() {
        doRight(target);
    }

    @CompilerControl(CompilerControl.Mode.DONT_INLINE)
    private boolean doLeft(Object t1) {
        return t1 == null;
    }

    @CompilerControl(CompilerControl.Mode.DONT_INLINE)
    private boolean doRight(Object t2) {
        return null == t2;
    }

    /*
        i7 4790K, 4.0 Ghz, Linux x86_64, JDK 9 (Shenandoah, 2016-09-05)

            Benchmark                     Mode  Cnt  Score   Error  Units

            # Shenandoah
            ACmpBarriersKnownNulls.left   avgt    5  2.235 ± 0.011  ns/op
            ACmpBarriersKnownNulls.right  avgt    5  2.240 ± 0.089  ns/op

            # G1
            ACmpBarriersKnownNulls.left   avgt    5  1.971 ± 0.001  ns/op
            ACmpBarriersKnownNulls.right  avgt    5  1.974 ± 0.021  ns/op

            # Parallel
            ACmpBarriersKnownNulls.left   avgt    5  1.977 ± 0.026  ns/op
            ACmpBarriersKnownNulls.right  avgt    5  1.973 ± 0.001  ns/op

        The difference is not caused by different compilation of doLeft/doRight methods,
        but rather the additional read barriers in the JMH loop itself. The generated code
        for doLeft/doRight in Shenandoah/G1/Parallel is the same:

                               [Verified Entry Point]
             11.16%    7.47%     0x00007f309d542240: mov    %eax,-0x14000(%rsp)
              0.15%    0.07%     0x00007f309d542247: push   %rbp
              0.22%    0.14%     0x00007f309d542248: sub    $0x10,%rsp
             11.05%   10.65%     0x00007f309d54224c: test   %rdx,%rdx
                              ╭  0x00007f309d54224f: je     0x00007f309d54225f
              0.10%    0.06%  │  0x00007f309d542251: xor    %eax,%eax
              0.11%    0.08%  │  0x00007f309d542253: add    $0x10,%rsp
             11.43%   11.21%  │  0x00007f309d542257: pop    %rbp
              0.07%    0.04%  │  0x00007f309d542258: test   %eax,0x18026da2(%rip)
              0.07%    0.01%  │  0x00007f309d54225e: retq
     */

}