Prevent ConsumeNextToken from inlining into ConsumeNextTokenOrRollback by EgorBo · Pull Request #126659 · dotnet/runtime

EgorBo · 2026-04-08T20:34:06Z

testing some theories

EgorBo · 2026-04-08T20:34:45Z

@EgorBot -linux_azure_arm -linux_aws_amd -linux_aws_arm -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");
    }
}

dotnet-policy-service · 2026-04-08T20:35:23Z

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

Copilot

Pull request overview

This PR improves Ascii.NarrowUtf16ToAscii throughput on ARM64 by unrolling the NEON (Vector128) inner loop to process 32 UTF-16 chars per iteration, aiming to better utilize modern ARM64 cores’ dual vector execution resources.

Changes:

Add a 2× unrolled ARM SIMD loop that loads 4× Vector128<ushort> (32 chars), checks for non-ASCII once, then stores 2× Vector128<byte> (32 bytes).
Convert the original do { ... } while (...) loop to a while (...) loop to avoid executing when the new unrolled loop fully drains the input.
Preserve the existing 1× vector loop as the fallback for remaining elements / non-ASCII detection.

src/libraries/System.Private.CoreLib/src/System/Text/Ascii.Utility.cs

EgorBo · 2026-04-08T22:34:30Z

@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");
    }
}

Copilot

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

Copilot · 2026-04-08T22:38:20Z

src/libraries/System.Text.Json/src/System/Text/Json/Reader/JsonReaderHelper.net8.cs

+        /// <summary>IndexOfAny('"', '\', less than 32)</summary>
        /// <remarks>https://tools.ietf.org/html/rfc8259</remarks>
-        private static readonly SearchValues<byte> s_controlQuoteBackslash = SearchValues.Create(
-            // Any Control, < 32 (' ')
-            "\u0000\u0001\u0002\u0003\u0004\u0005\u0006\u0007\u0008\u0009\u000A\u000B\u000C\u000D\u000E\u000F\u0010\u0011\u0012\u0013\u0014\u0015\u0016\u0017\u0018\u0019\u001A\u001B\u001C\u001D\u001E\u001F"u8 +
-            // Quote
-            "\""u8 +
-            // Backslash
-            "\\"u8);
+        public static unsafe int IndexOfQuoteOrAnyControlOrBackSlash(this ReadOnlySpan<byte> span)
+        {


This PR’s title/description focus on adding NoInlining to Utf8JsonReader.ConsumeNextToken, but this file also replaces the net8 implementation of IndexOfQuoteOrAnyControlOrBackSlash (SearchValues/Span.IndexOfAny) with a large custom unsafe+Vector scan. Please either (1) update the PR title/description to explain why this additional change is required and what perf/correctness data supports it, or (2) split it into a separate PR so the inlining change can be reviewed independently.

EgorBo · 2026-04-09T00:02:19Z

@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);
}

EgorBo · 2026-04-09T00:26:41Z

@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);
}

Copilot

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 4 comments.

Copilot · 2026-04-09T00:30:48Z

src/libraries/System.Private.CoreLib/src/System/SearchValues/IndexOfAnyAsciiSearcher.cs

            ref byte currentSearchSpace = ref searchSpace;

-            if (searchSpaceLength < sizeof(ulong))
+            if (AdvSimd.IsSupported || searchSpaceLength < sizeof(ulong))


The updated condition if (AdvSimd.IsSupported || searchSpaceLength < sizeof(ulong)) forces the scalar loop on ARM for all input lengths, bypassing the vectorized implementations below (including the existing AdvSimd code paths). This is likely a significant perf regression and is also inconsistent with similar methods in this file that gate on IsVectorizationSupported / length only. Consider reverting to the previous length-only check, or gating on !IsVectorizationSupported if the intent is to disable vectorization when no SIMD is available.

Suggested change

if (AdvSimd.IsSupported || searchSpaceLength < sizeof(ulong))

if (searchSpaceLength < sizeof(ulong))

Copilot · 2026-04-09T00:30:48Z

src/libraries/System.Private.CoreLib/src/System/SearchValues/IndexOfAnyAsciiSearcher.cs

+                if (AdvSimd.IsSupported && typeof(T) == typeof(byte))
+                {
+                    ulong matches = AdvSimd.ShiftRightLogicalNarrowingLower(result.AsUInt16(), 4).AsUInt64().ToScalar();
+                    return BitOperations.TrailingZeroCount(matches) >> 2 + (int)((nuint)Unsafe.ByteOffset(ref searchSpace, ref current) / (nuint)sizeof(T));


In the AdvSimd fast path, operator precedence makes the return expression compute TrailingZeroCount(matches) >> (2 + offset) instead of (TrailingZeroCount(matches) >> 2) + offset, which will produce incorrect indices. Add parentheses so the shift and the addition are applied in the intended order.

Suggested change

return BitOperations.TrailingZeroCount(matches) >> 2 + (int)((nuint)Unsafe.ByteOffset(ref searchSpace, ref current) / (nuint)sizeof(T));

return (BitOperations.TrailingZeroCount(matches) >> 2) + (int)((nuint)Unsafe.ByteOffset(ref searchSpace, ref current) / (nuint)sizeof(T));

Copilot · 2026-04-09T00:30:48Z

src/libraries/System.Private.CoreLib/src/System/SearchValues/IndexOfAnyAsciiSearcher.cs

+                if (AdvSimd.IsSupported && typeof(T) == typeof(byte))
+                {
+                    ulong matches = AdvSimd.ShiftRightLogicalNarrowingLower(result.AsUInt16(), 4).AsUInt64().ToScalar();
+                    return BitOperations.TrailingZeroCount(matches) >> 2 + (int)((nuint)Unsafe.ByteOffset(ref searchSpace, ref current) / (nuint)sizeof(T));
+                }
+


The AdvSimd branch computes matches via ShiftRightLogicalNarrowingLower(result.AsUInt16(), 4), which narrows 8x16-bit lanes to a 64-bit result. This transformation cannot represent all 16 byte lanes of the original Vector128<byte> (and AsUInt16() groups bytes into pairs), so a match in the upper half of the vector (or in the second byte of a pair) can yield an incorrect index. Unless there is a proven and correct packing scheme here, this path should either use the existing TNegator.ExtractMask(result) logic or implement a mask extraction that preserves per-byte lane positions across the full 128-bit vector.

Suggested change

if (AdvSimd.IsSupported && typeof(T) == typeof(byte))

{

ulong matches = AdvSimd.ShiftRightLogicalNarrowingLower(result.AsUInt16(), 4).AsUInt64().ToScalar();

return BitOperations.TrailingZeroCount(matches) >> 2 + (int)((nuint)Unsafe.ByteOffset(ref searchSpace, ref current) / (nuint)sizeof(T));

}

Copilot · 2026-04-09T00:30:49Z

src/libraries/System.Private.CoreLib/src/System/SearchValues/IndexOfAnyAsciiSearcher.cs

            ref byte currentSearchSpace = ref searchSpace;

-            if (searchSpaceLength < sizeof(ulong))
+            if (AdvSimd.IsSupported || searchSpaceLength < sizeof(ulong))


PR title/description mention preventing ConsumeNextToken inlining, but the changes in this diff are in IndexOfAnyAsciiSearcher and alter SIMD/scalar behavior and index computation. Please update the PR metadata to match the actual change being made (or move these changes to the intended location) so reviewers and release notes aren’t misled.

EgorBo · 2026-04-09T09:00:39Z

@EgorBot -arm -aws_arm -linux_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");
    }
}

EgorBo · 2026-04-09T09:29:38Z

@EgorBot -arm -aws_arm -linux_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");
    }
}

Copilot

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 2 comments.

Copilot · 2026-04-09T09:32:24Z

src/libraries/System.Text.Json/src/System/Text/Json/Reader/JsonReaderHelper.net8.cs

+            // Fast path for " in the first 16 bytes
+            if (Vector128.IsHardwareAccelerated && span.Length >= 16)
+            {
+                ref byte ptr = ref MemoryMarshal.GetReference(span);
+                Vector128<byte> matches = Vector128.Equals(Vector128.LoadUnsafe(ref ptr), Vector128.Create((byte)'"'));
+                if (AdvSimd.IsSupported)
+                {
+                    // TODO: use Vector128.IndexOf for both AdvSimd and Sse2 once
+                    ulong mask = AdvSimd.ShiftRightLogicalNarrowingLower(matches.AsUInt16(), 4).AsUInt64().ToScalar();
+                    if (mask != 0)
+                    {
+                        return BitOperations.TrailingZeroCount(mask) >> 2;
+                    }
+                }
+                else
+                {
+                    uint mask = matches.ExtractMostSignificantBits();
+                    if (mask != 0)
+                    {
+                        return BitOperations.TrailingZeroCount(mask);
+                    }
+                }
+            }


The new Vector128 fast-path only searches for the quote character ("), but this helper’s contract (and its callers) require returning the first occurrence of any of: quote, backslash, or any control character (< 0x20). If a backslash or control char appears before the closing quote within the first 16 bytes, this will now incorrectly return the quote index and skip required validation/escape handling. Please either remove this fast-path or extend it to compute the earliest index across all three conditions before returning.

Suggested change

// Fast path for " in the first 16 bytes

if (Vector128.IsHardwareAccelerated && span.Length >= 16)

{

ref byte ptr = ref MemoryMarshal.GetReference(span);

Vector128<byte> matches = Vector128.Equals(Vector128.LoadUnsafe(ref ptr), Vector128.Create((byte)'"'));

if (AdvSimd.IsSupported)

{

// TODO: use Vector128.IndexOf for both AdvSimd and Sse2 once

ulong mask = AdvSimd.ShiftRightLogicalNarrowingLower(matches.AsUInt16(), 4).AsUInt64().ToScalar();

if (mask != 0)

{

return BitOperations.TrailingZeroCount(mask) >> 2;

}

}

else

{

uint mask = matches.ExtractMostSignificantBits();

if (mask != 0)

{

return BitOperations.TrailingZeroCount(mask);

}

}

}

Copilot · 2026-04-09T09:32:24Z

src/libraries/System.Text.Json/src/System/Text/Json/Reader/JsonReaderHelper.net8.cs

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static int IndexOfQuoteOrAnyControlOrBackSlash(this ReadOnlySpan<byte> span) =>
-            span.IndexOfAny(s_controlQuoteBackslash);
+        public static int IndexOfQuoteOrAnyControlOrBackSlash(this ReadOnlySpan<byte> span)
+        {
+            // Fast path for " in the first 16 bytes
+            if (Vector128.IsHardwareAccelerated && span.Length >= 16)


PR title mentions preventing ConsumeNextToken from inlining into ConsumeNextTokenOrRollback, but the change here is a new SIMD fast-path inside IndexOfQuoteOrAnyControlOrBackSlash. If the intent is to affect inlining decisions, please document that relationship here (or adjust the PR title/description) so reviewers can understand why low-level string scanning logic is being changed for that purpose.

Copilot AI review requested due to automatic review settings April 8, 2026 20:34

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Benchmarks for dotnet/runtime#126659 (for @EgorBo) EgorBot/Benchmarks#96

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EgorBo force-pushed the arm64-narrow-unroll branch from 34c2bdd to 9e27b05 Compare April 8, 2026 21:30

EgorBo changed the title ~~Unroll ARM64 ASCII narrowing loop 2x in NarrowUtf16ToAscii~~ Prevent ConsumeNextToken from inlining into ConsumeNextTokenOrRollback Apr 8, 2026

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Benchmarks for dotnet/runtime#126659 (for @EgorBo) EgorBot/Benchmarks#97

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Benchmarks for dotnet/runtime#126659 (for @EgorBo) EgorBot/Benchmarks#103

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This was referenced Apr 9, 2026

Mono assertion running WASM trimming tests #126675

Open

System.Net.NameResolution.Tests DNS failures: Name or service not known #126641

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The Operation will be canceled. The next steps may not contain expected logs. dotnet/dnceng#3008

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[android-arm64] The Operation will be canceled. The next steps may not contain expected logs. dotnet/dnceng#6408

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optimize for arm64

3e2e8d3

EgorBo force-pushed the arm64-narrow-unroll branch from c243593 to 3e2e8d3 Compare April 9, 2026 08:59

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Benchmarks for dotnet/runtime#126659 (for @EgorBo) EgorBot/Benchmarks#109

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simpler impl

d148284

Copilot AI review requested due to automatic review settings April 9, 2026 09:29

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Benchmarks for dotnet/runtime#126659 (for @EgorBo) EgorBot/Benchmarks#110

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	if (AdvSimd.IsSupported \|\| searchSpaceLength < sizeof(ulong))
	if (searchSpaceLength < sizeof(ulong))

	return BitOperations.TrailingZeroCount(matches) >> 2 + (int)((nuint)Unsafe.ByteOffset(ref searchSpace, ref current) / (nuint)sizeof(T));
	return (BitOperations.TrailingZeroCount(matches) >> 2) + (int)((nuint)Unsafe.ByteOffset(ref searchSpace, ref current) / (nuint)sizeof(T));

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EgorBo commented Apr 8, 2026 •

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