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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
using Microsoft.Xunit.Performance;
using Microsoft.Xunit.Performance.Api;
using System;
using System.Reflection;
using Xunit;
[assembly: OptimizeForBenchmarks]
// Test code taken directly from GitHub issue #9692 (https://github.com/dotnet/coreclr/issues/9692)
// Laying the loop's early return path in-line can cost 30% on this micro-benchmark.
namespace Layout
{
public unsafe class SearchLoops
{
public static int Main(string[] args)
{
// Make sure equal strings compare as such
if (!LoopReturn("hello", "hello") || !LoopGoto("goodbye", "goodbye"))
{
return -1;
}
// Make sure not-equal strings compare as such
if (LoopReturn("hello", "goodbye") || LoopGoto("goodbye", "hello"))
{
return -1;
}
// Success
return 100;
}
public int length = 100;
private string test1;
private string test2;
public SearchLoops()
{
test1 = new string('A', length);
test2 = new string('A', length);
}
[Benchmark]
public void LoopReturn()
{
Benchmark.Iterate(() => LoopReturn(test1, test2));
}
[Benchmark]
public void LoopGoto()
{
Benchmark.Iterate(() => LoopGoto(test1, test2));
}
// Variant with code written naturally -- need JIT to lay this out
// with return path out of loop for best performance.
public static bool LoopReturn(String strA, String strB)
{
int length = strA.Length;
fixed (char* ap = strA) fixed (char* bp = strB)
{
char* a = ap;
char* b = bp;
while (length != 0)
{
int charA = *a;
int charB = *b;
if (charA != charB)
return false; // placement of prolog for this return is the issue
a++;
b++;
length--;
}
return true;
}
}
// Variant with code written awkwardly but which acheives the desired
// performance if JIT simply lays out code in source order.
public static bool LoopGoto(String strA, String strB)
{
int length = strA.Length;
fixed (char* ap = strA) fixed (char* bp = strB)
{
char* a = ap;
char* b = bp;
while (length != 0)
{
int charA = *a;
int charB = *b;
if (charA != charB)
goto ReturnFalse; // placement of prolog for this return is the issue
a++;
b++;
length--;
}
return true;
ReturnFalse:
return false;
}
}
}
}
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