Optimize IndexOfAnyAsciiSearcher on Arm64

[tannergooding]

This improves the codegen of the dedicated Count, IndexOf, and LastIndexOf APIs on Arm64 and correspondingly updates IndexOfAnyAsciiSearcher to consume them instead of ExtractMostSignificantBits

This is notably not strictly the "ideal" codegen as it still does an extra comparison, but that is something we can address in the JIT and should still provide a 5-50% performance increase in workloads using this API as part of their core loop.

[tannergooding]

@EgorBot -arm -linux_arm

using System.Buffers;
using BenchmarkDotNet.Attributes;

public class Benchmarks
{
    private static readonly SearchValues<byte> s_controlQuoteBackslash = SearchValues.Create(
        "\u0000\u0001\u0002\u0003\u0004\u0005\u0006\u0007\u0008\u0009\u000A\u000B"u8 +
        "\u000C\u000D\u000E\u000F\u0010\u0011\u0012\u0013\u0014\u0015\u0016\u0017\u0018"u8 +
        "\u0019\u001A\u001B\u001C\u001D\u001E\u001F"u8 + "\""u8 + "\\"u8);

    private byte[] _str = "Product description with some text that is a bit longer than usual\""u8.ToArray();

    [Benchmark]
    public int Medium() => _str.AsSpan().IndexOfAny(s_controlQuoteBackslash);
}

[tannergooding]

@EgorBot -linux_azure_arm -arm

using System.Text;
using System.Text.Json;
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;

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

[MemoryDiagnoser]
public class Benchmarks
{
    // ── TokenSerialization fields ────────────────────────────────────────────
    private List<object> _tokenObjects;
    [ThreadStatic] static Utf8JsonWriter t_writer;
    [ThreadStatic] static MemoryStream t_stream;

    [GlobalSetup]
    public void Setup()
    {
        // TokenSerialization
        _tokenObjects = new List<object>(200);
        for (int i = 0; i < 200; i++)
        {
            if (i % 3 == 0)
                _tokenObjects.Add(GenerateRecordJson(1));
            else
                _tokenObjects.Add(new Dictionary<string, object>
                {
                    ["seq"] = i,
                    ["label"] = $"item_{i}",
                    ["blob"] = new byte[100]
                });
        }
    }

    private static string GenerateRecordJson(int targetSizeKb = 150)
    {
        var sb = new StringBuilder(targetSizeKb * 1024 + 512);
        sb.Append("{");
        sb.Append("\"TypeName\":\"product\",");
        sb.Append("\"CategoryCode\":1,");
        sb.Append("\"Label\":\"Product\",");
        sb.Append("\"IsAction\":false,");
        sb.Append("\"IsActionMember\":false,");
        sb.Append("\"IsTrackingEnabled\":true,");
        sb.Append("\"IsAvailableLocal\":true,");
        sb.Append("\"IsChildRecord\":false,");
        sb.Append("\"IsLinksEnabled\":true,");
        sb.Append("\"IsCustomRecord\":false,");
        sb.Append("\"PrimaryKeyField\":\"productid\",");
        sb.Append("\"PrimaryLabelField\":\"title\",");
        sb.Append("\"Fields\":[");
        int targetBytes = targetSizeKb * 1024;
        int fieldIndex = 0;
        bool firstField = true;
        while (sb.Length < targetBytes - 512)
        {
            if (!firstField) sb.Append(",");
            firstField = false;
            sb.Append("{");
            sb.Append($"\"TypeName\":\"field_{fieldIndex}\",");
            sb.Append($"\"InternalName\":\"Field_{fieldIndex}\",");
            sb.Append($"\"FieldType\":\"String\",");
            sb.Append($"\"Label\":\"Field {fieldIndex}\",");
            sb.Append($"\"MaxSize\":100,");
            sb.Append($"\"IsReadable\":true,");
            sb.Append($"\"IsCreatable\":true,");
            sb.Append($"\"IsUpdatable\":true,");
            sb.Append($"\"IsTrackingEnabled\":false,");
            sb.Append($"\"IsPrimaryKey\":false,");
            sb.Append($"\"IsVirtual\":false,");
            sb.Append($"\"Requirement\":\"None\"");
            sb.Append("}");
            fieldIndex++;
        }
        sb.Append("]");
        sb.Append("}");
        return sb.ToString();
    }

    [Benchmark]
    public void TokenSerialization()
    {
        var stream = t_stream ??= new MemoryStream(64 * 1024);
        stream.Position = 0;
        stream.SetLength(0);
        var writer = t_writer;
        if (writer == null)
        {
            writer = new Utf8JsonWriter(stream, new JsonWriterOptions { SkipValidation = true });
            t_writer = writer;
        }
        else
            writer.Reset(stream);
        writer.WriteStartObject();
        writer.WriteStartArray("Catalog");
        foreach (var token in _tokenObjects)
        {
            if (token is string strToken)
            {
                if (!string.IsNullOrEmpty(strToken))
                    writer.WriteRawValue(strToken);
            }
            else if (token is Dictionary<string, object> dictToken)
            {
                writer.WriteStartObject();
                foreach (var kvp in dictToken)
                {
                    writer.WritePropertyName(kvp.Key);
                    JsonSerializer.Serialize(writer, kvp.Value);
                }
                writer.WriteEndObject();
            }
        }
        writer.WriteEndArray();
        writer.WriteEndObject();
        writer.Flush();
        if (stream.Length == 0) throw new Exception("unreachable");
    }
}

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-system-buffers
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

This PR adds an Arm64/AdvSimd-specific fast-path for computing the first match index from a Vector128<byte> match result in IndexOfAnyAsciiSearcher, aiming to reduce overhead in IndexOfAny-style searches.

Changes:

• Extended INegator with IndexOfFirstMatch(Vector128<byte> result) to centralize “find first match” logic.
• Implemented an AdvSimd-based first-match index computation for both DontNegate and Negate.
• Updated IndexOfAnyResultMapper’s Vector128 code paths to use the new IndexOfFirstMatch helper.

[EgorBo]

@EgorBot -aws_arm -profiler

using System.Buffers;
using BenchmarkDotNet.Attributes;

public class Benchmarks
{
    private static readonly SearchValues<byte> s_controlQuoteBackslash = SearchValues.Create(
        "\u0000\u0001\u0002\u0003\u0004\u0005\u0006\u0007\u0008\u0009\u000A\u000B"u8 +
        "\u000C\u000D\u000E\u000F\u0010\u0011\u0012\u0013\u0014\u0015\u0016\u0017\u0018"u8 +
        "\u0019\u001A\u001B\u001C\u001D\u001E\u001F"u8 + "\""u8 + "\\"u8);

    private byte[] _str = "Product description with some text that is a bit longer than usual\""u8.ToArray();

    [Benchmark]
    public int Medium() => _str.AsSpan().IndexOfAny(s_controlQuoteBackslash);
}

[EgorBo]

@EgorBot -aws_amd -profiler

using System.Text;
using System.Text.Json;
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;

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

[MemoryDiagnoser]
public class Benchmarks
{
    // ── TokenSerialization fields ────────────────────────────────────────────
    private List<object> _tokenObjects;
    [ThreadStatic] static Utf8JsonWriter t_writer;
    [ThreadStatic] static MemoryStream t_stream;

    [GlobalSetup]
    public void Setup()
    {
        // TokenSerialization
        _tokenObjects = new List<object>(200);
        for (int i = 0; i < 200; i++)
        {
            if (i % 3 == 0)
                _tokenObjects.Add(GenerateRecordJson(1));
            else
                _tokenObjects.Add(new Dictionary<string, object>
                {
                    ["seq"] = i,
                    ["label"] = $"item_{i}",
                    ["blob"] = new byte[100]
                });
        }
    }

    private static string GenerateRecordJson(int targetSizeKb = 150)
    {
        var sb = new StringBuilder(targetSizeKb * 1024 + 512);
        sb.Append("{");
        sb.Append("\"TypeName\":\"product\",");
        sb.Append("\"CategoryCode\":1,");
        sb.Append("\"Label\":\"Product\",");
        sb.Append("\"IsAction\":false,");
        sb.Append("\"IsActionMember\":false,");
        sb.Append("\"IsTrackingEnabled\":true,");
        sb.Append("\"IsAvailableLocal\":true,");
        sb.Append("\"IsChildRecord\":false,");
        sb.Append("\"IsLinksEnabled\":true,");
        sb.Append("\"IsCustomRecord\":false,");
        sb.Append("\"PrimaryKeyField\":\"productid\",");
        sb.Append("\"PrimaryLabelField\":\"title\",");
        sb.Append("\"Fields\":[");
        int targetBytes = targetSizeKb * 1024;
        int fieldIndex = 0;
        bool firstField = true;
        while (sb.Length < targetBytes - 512)
        {
            if (!firstField) sb.Append(",");
            firstField = false;
            sb.Append("{");
            sb.Append($"\"TypeName\":\"field_{fieldIndex}\",");
            sb.Append($"\"InternalName\":\"Field_{fieldIndex}\",");
            sb.Append($"\"FieldType\":\"String\",");
            sb.Append($"\"Label\":\"Field {fieldIndex}\",");
            sb.Append($"\"MaxSize\":100,");
            sb.Append($"\"IsReadable\":true,");
            sb.Append($"\"IsCreatable\":true,");
            sb.Append($"\"IsUpdatable\":true,");
            sb.Append($"\"IsTrackingEnabled\":false,");
            sb.Append($"\"IsPrimaryKey\":false,");
            sb.Append($"\"IsVirtual\":false,");
            sb.Append($"\"Requirement\":\"None\"");
            sb.Append("}");
            fieldIndex++;
        }
        sb.Append("]");
        sb.Append("}");
        return sb.ToString();
    }

    [Benchmark]
    public void TokenSerialization()
    {
        var stream = t_stream ??= new MemoryStream(64 * 1024);
        stream.Position = 0;
        stream.SetLength(0);
        var writer = t_writer;
        if (writer == null)
        {
            writer = new Utf8JsonWriter(stream, new JsonWriterOptions { SkipValidation = true });
            t_writer = writer;
        }
        else
            writer.Reset(stream);
        writer.WriteStartObject();
        writer.WriteStartArray("Catalog");
        foreach (var token in _tokenObjects)
        {
            if (token is string strToken)
            {
                if (!string.IsNullOrEmpty(strToken))
                    writer.WriteRawValue(strToken);
            }
            else if (token is Dictionary<string, object> dictToken)
            {
                writer.WriteStartObject();
                foreach (var kvp in dictToken)
                {
                    writer.WritePropertyName(kvp.Key);
                    JsonSerializer.Serialize(writer, kvp.Value);
                }
                writer.WriteEndObject();
            }
        }
        writer.WriteEndArray();
        writer.WriteEndObject();
        writer.Flush();
        if (stream.Length == 0) throw new Exception("unreachable");
    }
}