Use IndexOfAnyValues in the RegexCompiler and source gen

src/libraries/System.Text.RegularExpressions/gen/RegexGenerator.cs

@@ -198,6 +198,7 @@ x.Options is CSharpCompilationOptions options ?
                 // a user's partial type.  We can now rely on binding rules mapping to these usings and don't need to
                 // use global-qualified names for the rest of the implementation.
                 writer.WriteLine($"    using System;");
+                writer.WriteLine($"    using System.Buffers;");
                 writer.WriteLine($"    using System.CodeDom.Compiler;");
                 writer.WriteLine($"    using System.Collections;");
                 writer.WriteLine($"    using System.ComponentModel;");
@@ -240,7 +241,7 @@ x.Options is CSharpCompilationOptions options ?
                     writer.WriteLine($"{{");
                     writer.Indent++;
                     bool sawFirst = false;
-                    foreach (KeyValuePair<string, string[]> helper in requiredHelpers)
+                    foreach (KeyValuePair<string, string[]> helper in requiredHelpers.OrderBy(h => h.Key, StringComparer.Ordinal))
                     {
                         if (sawFirst)
                         {

src/libraries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/CompiledRegexRunner.cs

@@ -1,27 +1,32 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Buffers;
 using System.Globalization;
 
 namespace System.Text.RegularExpressions
 {
     internal sealed class CompiledRegexRunner : RegexRunner
     {
         private readonly ScanDelegate _scanMethod;
-        /// <summary>This field will only be set if the pattern contains backreferences and has RegexOptions.IgnoreCase</summary>
-        private readonly CultureInfo? _culture;
 
 #pragma warning disable CA1823 // Avoid unused private fields. Justification: Used via reflection to cache the Case behavior if needed.
 #pragma warning disable CS0169
+        private readonly IndexOfAnyValues<char>[]? _indexOfAnyValues;
+
+        /// <summary>This field will only be set if the pattern contains backreferences and has RegexOptions.IgnoreCase</summary>
+        private readonly CultureInfo? _culture;
+
         private RegexCaseBehavior _caseBehavior;
 #pragma warning restore CS0169
 #pragma warning restore CA1823
 
         internal delegate void ScanDelegate(RegexRunner runner, ReadOnlySpan<char> text);
 
-        public CompiledRegexRunner(ScanDelegate scan, CultureInfo? culture)
+        public CompiledRegexRunner(ScanDelegate scan, IndexOfAnyValues<char>[]? indexOfAnyValues, CultureInfo? culture)
         {
             _scanMethod = scan;
+            _indexOfAnyValues = indexOfAnyValues;
             _culture = culture;
         }
 

src/libraries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/CompiledRegexRunnerFactory.cs

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Buffers;
 using System.Globalization;
 using System.Reflection.Emit;
 
@@ -9,20 +10,22 @@ namespace System.Text.RegularExpressions
     internal sealed class CompiledRegexRunnerFactory : RegexRunnerFactory
     {
         private readonly DynamicMethod _scanMethod;
+        private readonly IndexOfAnyValues<char>[]? _indexOfAnyValues;
         /// <summary>This field will only be set if the pattern has backreferences and uses RegexOptions.IgnoreCase</summary>
         private readonly CultureInfo? _culture;
 
         // Delegate is lazily created to avoid forcing JIT'ing until the regex is actually executed.
         private CompiledRegexRunner.ScanDelegate? _scan;
 
-        public CompiledRegexRunnerFactory(DynamicMethod scanMethod, CultureInfo? culture)
+        public CompiledRegexRunnerFactory(DynamicMethod scanMethod, IndexOfAnyValues<char>[]? indexOfAnyValues, CultureInfo? culture)
         {
             _scanMethod = scanMethod;
+            _indexOfAnyValues = indexOfAnyValues;
             _culture = culture;
         }
 
         protected internal override RegexRunner CreateInstance() =>
             new CompiledRegexRunner(
-                _scan ??= _scanMethod.CreateDelegate<CompiledRegexRunner.ScanDelegate>(), _culture);
+                _scan ??= _scanMethod.CreateDelegate<CompiledRegexRunner.ScanDelegate>(), _indexOfAnyValues, _culture);
     }
 }

src/libraries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/RegexCharClass.cs

@@ -3,6 +3,7 @@
 
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 using System.Numerics;
 using System.Runtime.CompilerServices;
@@ -839,6 +840,22 @@ public static int GetSetChars(string set, Span<char> chars)
             return count;
         }
 
+        public static bool TryGetAsciiSetChars(string set, [NotNullWhen(true)] out char[]? asciiChars)
+        {
+            Span<char> chars = stackalloc char[128];
+
+            chars = chars.Slice(0, GetSetChars(set, chars));
+
+            if (chars.IsEmpty || !IsAscii(chars))
+            {
+                asciiChars = null;
+                return false;
+            }
+
+            asciiChars = chars.ToArray();
+            return true;
+        }
+
         /// <summary>
         /// Determines whether two sets may overlap.
         /// </summary>