Remove object[] allocation from CustomAttribute.AddCustomAttributes

[stephentoub]

Method	Toolchain	Mean	Ratio	Allocated	Alloc Ratio
GetCustomAttributes	\main\corerun.exe	888.7 ns	1.00	296 B	1.00
GetCustomAttributes	\pr\corerun.exe	829.7 ns	0.94	232 B	0.78

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;
using System;

[MemoryDiagnoser(false)]
public class Program
{
    static void Main(string[] args) => BenchmarkSwitcher.FromAssembly(typeof(Program).Assembly).Run(args);

    [Benchmark]
    public object[] GetCustomAttributes() => typeof(C).GetCustomAttributes(typeof(MyAttribute), true);
}

[My(Value1 = 1, Value2 = 2)]
class C { }

[AttributeUsage(AttributeTargets.All)]
public class MyAttribute : Attribute
{
    public int Value1 { get; set; }
    public int Value2 { get; set; }
}

[ghost]

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Issue Details

---

Method	Toolchain	Mean	Ratio	Allocated	Alloc Ratio
GetCustomAttributes	\main\corerun.exe	888.7 ns	1.00	296 B	1.00
GetCustomAttributes	\pr\corerun.exe	829.7 ns	0.94	232 B	0.78

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;
using System;

[MemoryDiagnoser(false)]
public class Program
{
    static void Main(string[] args) => BenchmarkSwitcher.FromAssembly(typeof(Program).Assembly).Run(args);

    [Benchmark]
    public object[] GetCustomAttributes() => typeof(C).GetCustomAttributes(typeof(MyAttribute), true);
}

[My(Value1 = 1, Value2 = 2)]
class C { }

[AttributeUsage(AttributeTargets.All)]
public class MyAttribute : Attribute
{
    public int Value1 { get; set; }
    public int Value2 { get; set; }
}

Author:	stephentoub
Assignees:	stephentoub
Labels:	area-System.Reflection
Milestone:	-