Fix string.Split regression

[hamarb123]

Fixes #130418 (probably).

/cc @tannergooding

[hamarb123]

Nevermind, this won't fix it - misread the platform - will re-open when I fix the code.

[dotnet-policy-service]

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[hamarb123]

@EgorBot -amd -arm -intel

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;
using System.IO;
using System.Threading;
using System.Threading.Tasks;

BenchmarkSwitcher.FromAssembly(typeof(Bench).Assembly).Run(args);

public class Bench
{
        [Benchmark]
        [Arguments("A B C D E F G H I J K L M N O P Q R S T U V W X Y Z", new char[] { ' ' }, StringSplitOptions.None)]
        [Arguments("A B C D E F G H I J K L M N O P Q R S T U V W X Y Z", new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries)]
        [Arguments("ABCDEFGHIJKLMNOPQRSTUVWXYZ", new char[]{' '}, StringSplitOptions.None)]
        [Arguments("ABCDEFGHIJKLMNOPQRSTUVWXYZ", new char[]{' '}, StringSplitOptions.RemoveEmptyEntries)]
        public string[] Split(string s, char[] arr, StringSplitOptions options)
            => s.Split(arr, options);
}

[hamarb123]

@MihuBot -arm

[hamarb123]

@EgorBot -ubuntu24_azure_cobalt100

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;
using System.IO;
using System.Threading;
using System.Threading.Tasks;

BenchmarkSwitcher.FromAssembly(typeof(Bench).Assembly).Run(args);

public class Bench
{
        [Benchmark]
        [Arguments("A B C D E F G H I J K L M N O P Q R S T U V W X Y Z", new char[] { ' ' }, StringSplitOptions.None)]
        [Arguments("A B C D E F G H I J K L M N O P Q R S T U V W X Y Z", new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries)]
        [Arguments("ABCDEFGHIJKLMNOPQRSTUVWXYZ", new char[]{' '}, StringSplitOptions.None)]
        [Arguments("ABCDEFGHIJKLMNOPQRSTUVWXYZ", new char[]{' '}, StringSplitOptions.RemoveEmptyEntries)]
        public string[] Split(string s, char[] arr, StringSplitOptions options)
            => s.Split(arr, options);
}

[EgorBo]

please don't replace safe code with unsafe

[hamarb123]

It was unsafe before the PR that introduced the regression. Part of the regression is likely the bounds check that exists here now.

[hamarb123]

That PR removed a lot more unsafe than just this one spot, and we only need to add this one spot back to get no bounds checks - surely that is fine?

[hamarb123]

@EgorBot -ubuntu24_azure_cobalt100

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;
using System.IO;
using System.Threading;
using System.Threading.Tasks;

BenchmarkSwitcher.FromAssembly(typeof(Bench).Assembly).Run(args);

public class Bench
{
        [Benchmark]
        [Arguments("A B C D E F G H I J K L M N O P Q R S T U V W X Y Z", new char[] { ' ' }, StringSplitOptions.None)]
        [Arguments("A B C D E F G H I J K L M N O P Q R S T U V W X Y Z", new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries)]
        [Arguments("ABCDEFGHIJKLMNOPQRSTUVWXYZ", new char[]{' '}, StringSplitOptions.None)]
        [Arguments("ABCDEFGHIJKLMNOPQRSTUVWXYZ", new char[]{' '}, StringSplitOptions.RemoveEmptyEntries)]
        public string[] Split(string s, char[] arr, StringSplitOptions options)
            => s.Split(arr, options);
}