前一段时间.Net源码有关Array下IndexOf性能优化,说是Array,还是跟Span有关,主要是Array下IndexOf和Span下Contains在值类型(int和long),会调用SpanHelp.T.cs文件中的IndexOfValueType方法.这次是使用指令集(向量)优化.
- 具体的issue: Vectorize SpanHelpers<T>.IndexOf (#60974)
using System;
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Order;
namespace CSharpBenchmarks.SpanTest
{
[MemoryDiagnoser]
[DisassemblyDiagnoser(printSource: true)]
[Orderer(SummaryOrderPolicy.FastestToSlowest)]
public class IndexOfTest
{
public byte[] bytes = new byte[] { 0, 0, 0, 0, 71, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 71, 0, 1, 0, 0, 0, 0, 1, 1, 0, 2, 0, 1, 1, 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 1, 0 };
public byte[] searchBytes = new byte[] { 0, 1, 0, 0 };
[Params(1024, 2048)]
public int Times { get; set; }
[Benchmark]
public int SpanIndexOf()
{
int sum = 0;
for (int i = 0; i < Times; i )
{
sum = bytes.AsSpan().IndexOf(searchBytes);
}
return sum;
}
[Benchmark]
public int SpanLastIndexOf()
{
int sum = 0;
for (int i = 0; i < Times; i )
{
sum = bytes.AsSpan().LastIndexOf(searchBytes);
}
return sum;
}
}
}
测试在.Net 7中Array和Span的IndexOf方法性能改进
从测试结果得出:IndexOf在.Net 7上相对.Net 6提升了71%,LastIndexOf在.Net 7上相对.Net 6提升36%(提升没那么多).因为是指令集优化,生成的汇编代码比较多,这里就就不贴了.
我们可以学习IndexOfValueType源码:
internal static unsafe int IndexOfValueType<T>(ref T searchSpace, T value, int length) where T : struct, IEquatable<T>
{
Debug.Assert(length >= 0);
nint index = 0; // Use nint for arithmetic to avoid unnecessary 64->32->64 truncations
if (Vector.IsHardwareAccelerated && Vector<T>.IsTypeSupported && (Vector<T>.Count * 2) <= length)
{
Vector<T> valueVector = new Vector<T>(value);
Vector<T> compareVector = default;
Vector<T> matchVector = default;
if ((uint)length % (uint)Vector<T>.Count != 0)
{
// Number of elements is not a multiple of Vector<T>.Count, so do one
// check and shift only enough for the remaining set to be a multiple
// of Vector<T>.Count.
compareVector = Unsafe.As<T, Vector<T>>(ref Unsafe.Add(ref searchSpace, index));
matchVector = Vector.Equals(valueVector, compareVector);
if (matchVector != Vector<T>.Zero)
{
goto VectorMatch;
}
index = length % Vector<T>.Count;
length -= length % Vector<T>.Count;
}
while (length > 0)
{
compareVector = Unsafe.As<T, Vector<T>>(ref Unsafe.Add(ref searchSpace, index));
matchVector = Vector.Equals(valueVector, compareVector);
if (matchVector != Vector<T>.Zero)
{
goto VectorMatch;
}
index = Vector<T>.Count;
length -= Vector<T>.Count;
}
goto NotFound;
VectorMatch:
for (int i = 0; i < Vector<T>.Count; i )
if (compareVector[i].Equals(value))
return (int)(index i);
}
while (length >= 8)
{
if (value.Equals(Unsafe.Add(ref searchSpace, index)))
goto Found;
if (value.Equals(Unsafe.Add(ref searchSpace, index 1)))
goto Found1;
if (value.Equals(Unsafe.Add(ref searchSpace, index 2)))
goto Found2;
if (value.Equals(Unsafe.Add(ref searchSpace, index 3)))
goto Found3;
if (value.Equals(Unsafe.Add(ref searchSpace, index 4)))
goto Found4;
if (value.Equals(Unsafe.Add(ref searchSpace, index 5)))
goto Found5;
if (value.Equals(Unsafe.Add(ref searchSpace, index 6)))
goto Found6;
if (value.Equals(Unsafe.Add(ref searchSpace, index 7)))
goto Found7;
length -= 8;
index = 8;
}
while (length >= 4)
{
if (value.Equals(Unsafe.Add(ref searchSpace, index)))
goto Found;
if (value.Equals(Unsafe.Add(ref searchSpace, index 1)))
goto Found1;
if (value.Equals(Unsafe.Add(ref searchSpace, index 2)))
goto Found2;
if (value.Equals(Unsafe.Add(ref searchSpace, index 3)))
goto Found3;
length -= 4;
index = 4;
}
while (length > 0)
{
if (value.Equals(Unsafe.Add(ref searchSpace, index)))
goto Found;
index = 1;
length--;
}
NotFound:
return -1;
Found: // Workaround for https://github.com/dotnet/runtime/issues/8795
return (int)index;
Found1:
return (int)(index 1);
Found2:
return (int)(index 2);
Found3:
return (int)(index 3);
Found4:
return (int)(index 4);
Found5:
return (int)(index 5);
Found6:
return (int)(index 6);
Found7:
return (int)(index 7);
}
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