Add is pattern benchmarks

src/Compilers/CSharp/Portable/Lowering/LocalRewriter/LocalRewriter_IsPatternOperator.cs

@@ -13,8 +13,9 @@ namespace Microsoft.CodeAnalysis.CSharp
     internal sealed partial class LocalRewriter
     {
         /// <summary>
-        /// Benchmark results (see https://github.com/dotnet/roslyn/pull/84961) show that short patterns can be more
-        /// efficient when emitted as comparisons. Larger patterns can benefit from switch dispatch.
+        /// Benchmarks in <c>src/Tools/Benchmarks/IsPatternBenchmarks.cs</c> show that short sparse patterns can be more
+        /// efficient as comparisons, while the sparse and dense four-value cases show that larger patterns can benefit
+        /// from general decision-DAG dispatch.
         /// </summary>
         private const int MaxTestsForInvertedLinearSequence = 3;
 

src/Tools/Benchmarks/IsPatternBenchmarks.cs

@@ -0,0 +1,164 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Runtime.CompilerServices;
+using BenchmarkDotNet.Attributes;
+
+namespace Benchmarks;
+
+public enum IsPatternInputPosition
+{
+    FirstHit,
+    LastHit,
+    Miss,
+}
+
+public enum IsPatternPathInput
+{
+    Empty,
+    Slash,
+    Backslash,
+    Other,
+}
+
+/// <summary>
+/// The pattern and comparison forms are expected to have equivalent performance when short patterns use linear
+/// lowering. This benchmark detects regressions in that equivalence.
+/// </summary>
+/// <seealso href="https://github.com/dotnet/roslyn/issues/80052"/>
+[EvaluateOverhead(false)]
+public class IsPatternLeadingSlashBenchmarks
+{
+    private string _path = null!;
+
+    [Params(IsPatternPathInput.Empty, IsPatternPathInput.Slash, IsPatternPathInput.Backslash, IsPatternPathInput.Other)]
+    public IsPatternPathInput Input { get; set; }
+
+    [GlobalSetup]
+    public void Setup()
+    {
+        _path = Input switch
+        {
+            IsPatternPathInput.Empty => "",
+            IsPatternPathInput.Slash => "/path",
+            IsPatternPathInput.Backslash => "\\path",
+            IsPatternPathInput.Other => "path",
+            _ => throw new InvalidOperationException(),
+        };
+    }
+
+    [Benchmark(Baseline = true)]
+    public bool Comparisons() => HasLeadingSlashWithComparisons(_path);
+
+    [Benchmark]
+    public bool Pattern() => HasLeadingSlashWithPattern(_path);
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static bool HasLeadingSlashWithComparisons(ReadOnlySpan<char> path)
+    {
+        if (path.Length > 0 && (path[0] == '/' || path[0] == '\\'))
+            return true;
+
+        return false;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static bool HasLeadingSlashWithPattern(ReadOnlySpan<char> path)
+    {
+        if (path.Length > 0 && path[0] is '/' or '\\')
+            return true;
+
+        return false;
+    }
+}
+
+/// <summary>
+/// The pattern and comparison forms are expected to have equivalent performance when short patterns use linear
+/// lowering. This benchmark detects regressions in that equivalence.
+/// </summary>
+/// <seealso href="https://github.com/dotnet/runtime/pull/132452"/>
+[EvaluateOverhead(false)]
+public class IsPatternJsonTerminatorBenchmarks : IsPatternByteInputBenchmarks
+{
+    protected override byte FirstCase => (byte)'.';
+    protected override byte LastCase => (byte)'e';
+
+    [Benchmark(Baseline = true)]
+    public int Comparisons()
+    {
+        var value = Value;
+        return value != (byte)'.' && value != (byte)'E' && value != (byte)'e'
+            ? value + 1
+            : value - 1;
+    }
+
+    [Benchmark]
+    public int Pattern()
+    {
+        var value = Value;
+        return value is not ((byte)'.' or (byte)'E' or (byte)'e')
+            ? value + 1
+            : value - 1;
+    }
+}
+
+/// <summary>
+/// Compares explicit linear tests with general decision-DAG dispatch for four sparse values.
+/// </summary>
+/// <seealso href="https://github.com/dotnet/roslyn/pull/84961"/>
+[EvaluateOverhead(false)]
+public class IsPatternSparseFourValueBenchmarks : IsPatternByteInputBenchmarks
+{
+    protected override byte FirstCase => (byte)'+';
+    protected override byte LastCase => (byte)'e';
+
+    [Benchmark(Baseline = true)]
+    public bool Comparisons() => Guard && (Value == (byte)'+' || Value == (byte)'.' || Value == (byte)'E' || Value == (byte)'e');
+
+    [Benchmark]
+    public bool Pattern() => Guard && Value is (byte)'+' or (byte)'.' or (byte)'E' or (byte)'e';
+}
+
+/// <summary>
+/// Compares explicit linear tests with general decision-DAG dispatch for four dense values.
+/// </summary>
+/// <seealso href="https://github.com/dotnet/roslyn/pull/84961"/>
+[EvaluateOverhead(false)]
+public class IsPatternDenseFourValueBenchmarks : IsPatternByteInputBenchmarks
+{
+    protected override byte FirstCase => 1;
+    protected override byte LastCase => 4;
+
+    [Benchmark(Baseline = true)]
+    public bool Comparisons() => Guard && (Value == 1 || Value == 2 || Value == 3 || Value == 4);
+
+    [Benchmark]
+    public bool Pattern() => Guard && Value is 1 or 2 or 3 or 4;
+}
+
+public abstract class IsPatternByteInputBenchmarks
+{
+    [Params(IsPatternInputPosition.FirstHit, IsPatternInputPosition.LastHit, IsPatternInputPosition.Miss)]
+    public IsPatternInputPosition Input { get; set; }
+
+    protected bool Guard;
+    protected byte Value;
+
+    protected abstract byte FirstCase { get; }
+    protected abstract byte LastCase { get; }
+
+    [GlobalSetup]
+    public void Setup()
+    {
+        Guard = true;
+        Value = Input switch
+        {
+            IsPatternInputPosition.FirstHit => FirstCase,
+            IsPatternInputPosition.LastHit => LastCase,
+            IsPatternInputPosition.Miss => byte.MaxValue,
+            _ => throw new InvalidOperationException(),
+        };
+    }
+}