/*
 * Copyright (c) 2017, Red Hat Inc. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * 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.writes;

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 WriteBarriersKnownNull {

    Target target;

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

    @Benchmark
    @CompilerControl(CompilerControl.Mode.DONT_INLINE)
    public void test() {
        target.field = null;
    }

    static class Target {
        Object field;
    }

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

            Benchmark                    Mode  Cnt  Score   Error  Units

            # Shenandoah
            WriteBarriersKnownNull.test  avgt   25  2.637 ± 0.027  ns/op

            # G1
            WriteBarriersKnownNull.test  avgt   25  1.958 ± 0.006  ns/op

            # Parallel
            WriteBarriersKnownNull.test  avgt   25  1.832 ± 0.097  ns/op

        Mostly the same as the regular barrier, plus the optimized out redundant nullchecks
        for stored value.

        Shenandoah:

                             [Verified Entry Point]
          9.60%   11.27%       0x00007f7031af6f40: mov    %eax,-0x14000(%rsp)
          0.02%                0x00007f7031af6f47: push   %rbp
                               0x00007f7031af6f48: sub    $0x10,%rsp
         10.13%   10.60%       0x00007f7031af6f4c: mov    -0x8(%rsi),%r10       ; <--- read barrier
                   0.02%       0x00007f7031af6f50: mov    0xc(%r10),%r11d       ; get field $target
          0.07%                0x00007f7031af6f54: test   %r11d,%r11d           ; null check $target <--- NOT IMPLICIT
                               0x00007f7031af6f57: je     0x00007f7031af6fc7
          9.91%   10.59%       0x00007f7031af6f59: mov    %r11,%r10
                               0x00007f7031af6f5c: mov    -0x8(%r10),%rbx       ; <--- read barrier AGAIN
          0.18%    0.12%       0x00007f7031af6f60: cmpb   $0x0,0x3d8(%r15)      ; "evacuation in progress?"
          0.02%                0x00007f7031af6f68: mov    -0x8(%r10),%rbx       ; <--- read barrier (in sequence)
         10.08%    8.85%  ╭    0x00007f7031af6f6c: je     0x00007f7031af6f79    ; no evacuation in progress, jump over <--- SHOULD BE MOVED TO SLOWPATH
                          │    0x00007f7031af6f6e: xchg   %rax,%rbx
                          │    0x00007f7031af6f71: callq  Stub::shenandoah_wb
                          │    0x00007f7031af6f76: xchg   %rax,%rbx
                          ↘    0x00007f7031af6f79: movsbl 0x378(%r15),%r11d     ; SATB test
                               0x00007f7031af6f81: test   %r11d,%r11d
                           ╭   0x00007f7031af6f84: jne    0x00007f7031af6f96
                           │↗  0x00007f7031af6f86: mov    %r12d,0xc(%rbx)       ; field store
         25.14%   22.09%   ││  0x00007f7031af6f8a: add    $0x10,%rsp
                           ││  0x00007f7031af6f8e: pop    %rbp
                           ││  0x00007f7031af6f8f: test   %eax,0x1286706b(%rip)
                           ││  0x00007f7031af6f95: retq


        G1:

                            [Verified Entry Point]
          7.45%    6.58%      0x00007f3204840cc0: mov    %eax,-0x14000(%rsp)
          5.74%    6.06%      0x00007f3204840cc7: push   %rbp
          7.74%    7.35%      0x00007f3204840cc8: sub    $0x10,%rsp
          0.18%    0.18%      0x00007f3204840ccc: mov    0xc(%rsi),%ebp         ; get field $target
          5.84%    6.56%      0x00007f3204840ccf: mov    0xc(%rbp),%r10d        ; <--- read old for SATB, plus NPE check
         18.27%   20.87%      0x00007f3204840cd3: movsbl 0x378(%r15),%r8d       ; SATB test
          0.02%    0.02%      0x00007f3204840cdb: test   %r8d,%r8d
                          ╭   0x00007f3204840cde: jne    0x00007f3204840cf0
                          │↗  0x00007f3204840ce0: mov    %r12d,0xc(%rbp)        ; field store
          4.11%    4.73%  ││  0x00007f3204840ce4: add    $0x10,%rsp
          9.60%   10.33%  ││  0x00007f3204840ce8: pop    %rbp
          0.30%    0.33%  ││  0x00007f3204840ce9: test   %eax,0x11f29311(%rip)
                   0.02%  ││  0x00007f3204840cef: retq

     */

}