Implement support for C# 11 switch on (ReadOnly)Span<char>.

ICSharpCode.Decompiler.Tests/Helpers/Tester.VB.cs

@@ -60,13 +60,16 @@ namespace ICSharpCode.Decompiler.Tests.Helpers
 				var vbcPath = roslynToolset.GetVBCompiler(roslynVersion);
 
 				IEnumerable<string> references;
+				string libPath;
 				if ((flags & CompilerOptions.UseRoslynMask) != 0 && (flags & CompilerOptions.TargetNet40) == 0)
 				{
 					references = coreDefaultReferences.Select(r => "-r:\"" + r + "\"");
+					libPath = coreRefAsmPath;
 				}
 				else
 				{
 					references = defaultReferences.Select(r => "-r:\"" + r + "\"");
+					libPath = RefAsmPath;
 				}
 				if (flags.HasFlag(CompilerOptions.ReferenceVisualBasic))
 				{
@@ -116,7 +119,7 @@ namespace ICSharpCode.Decompiler.Tests.Helpers
 				}
 
 				var command = Cli.Wrap(vbcPath)
-					.WithArguments($"{otherOptions}{string.Join(" ", references)} -out:\"{Path.GetFullPath(results.PathToAssembly)}\" {string.Join(" ", sourceFileNames.Select(fn => '"' + Path.GetFullPath(fn) + '"'))}")
+					.WithArguments($"{otherOptions}-libpath:\"{libPath}\" {string.Join(" ", references)} -out:\"{Path.GetFullPath(results.PathToAssembly)}\" {string.Join(" ", sourceFileNames.Select(fn => '"' + Path.GetFullPath(fn) + '"'))}")
 					.WithValidation(CommandResultValidation.None);
 				Console.WriteLine($"\"{command.TargetFilePath}\" {command.Arguments}");
 

ICSharpCode.Decompiler.Tests/Helpers/Tester.cs

@@ -295,6 +295,7 @@ namespace ICSharpCode.Decompiler.Tests.Helpers
 				"System.Linq.Expressions.dll",
 				"System.Linq.Queryable.dll",
 				"System.IO.FileSystem.Watcher.dll",
+				"System.Memory.dll",
 				"System.Threading.dll",
 				"System.Threading.Thread.dll",
 				"System.Runtime.dll",

ICSharpCode.Decompiler.Tests/TestCases/Pretty/Switch.cs

@@ -1509,5 +1509,54 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 					break;
 			}
 		}
+
+
+#if CS110 && NET70
+		public static string SwitchOverReadOnlySpanChar1(ReadOnlySpan<char> text)
+		{
+			Console.WriteLine("SwitchOverReadOnlySpanChar1:");
+			switch (text)
+			{
+				case "First case":
+					return "Text1";
+				case "Second case":
+				case "2nd case":
+					return "Text2";
+				case "Third case":
+					return "Text3";
+				case "Fourth case":
+					return "Text4";
+				case "Fifth case":
+					return "Text5";
+				case "Sixth case":
+					return "Text6";
+				default:
+					return "Default";
+			}
+		}
+
+		public static string SwitchOverSpanChar1(Span<char> text)
+		{
+			Console.WriteLine("SwitchOverSpanChar1:");
+			switch (text)
+			{
+				case "First case":
+					return "Text1";
+				case "Second case":
+				case "2nd case":
+					return "Text2";
+				case "Third case":
+					return "Text3";
+				case "Fourth case":
+					return "Text4";
+				case "Fifth case":
+					return "Text5";
+				case "Sixth case":
+					return "Text6";
+				default:
+					return "Default";
+			}
+		}
+#endif
 	}
 }

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -3898,7 +3898,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			{
 				value = Translate(strToInt.Argument)
 					.ConvertTo(
-						typeSystem.FindType(KnownTypeCode.String),
+						strToInt.ExpectedType,
 						this,
 						allowImplicitConversion: false // switch-expression does not support implicit conversions
 					);

ICSharpCode.Decompiler/CSharp/StatementBuilder.cs

@@ -214,7 +214,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			{
 				value = exprBuilder.Translate(strToInt.Argument)
 					.ConvertTo(
-						typeSystem.FindType(KnownTypeCode.String),
+						strToInt.ExpectedType,
 						exprBuilder,
 						// switch statement does support implicit conversions in general, however, the rules are
 						// not very intuitive and in order to prevent bugs, we emit an explicit cast.

ICSharpCode.Decompiler/DecompilerSettings.cs

@@ -1206,6 +1206,24 @@ namespace ICSharpCode.Decompiler
 			}
 		}
 
+		bool switchOnReadOnlySpanChar = true;
+
+		/// <summary>
+		/// Gets/Sets whether to use C# 11.0 switch on (ReadOnly)Span&lt;char&gt;
+		/// </summary>
+		[Category("C# 11.0 / VS 2022.4")]
+		[Description("DecompilerSettings.SwitchOnReadOnlySpanChar")]
+		public bool SwitchOnReadOnlySpanChar {
+			get { return switchOnReadOnlySpanChar; }
+			set {
+				if (switchOnReadOnlySpanChar != value)
+				{
+					switchOnReadOnlySpanChar = value;
+					OnPropertyChanged();
+				}
+			}
+		}
+
 		bool unsignedRightShift = true;
 
 		/// <summary>

ICSharpCode.Decompiler/IL/Instructions/StringToInt.cs

@@ -20,21 +20,26 @@
 
 using System.Collections.Generic;
 
+using ICSharpCode.Decompiler.TypeSystem;
+
 namespace ICSharpCode.Decompiler.IL
 {
 	partial class StringToInt
 	{
 		public List<(string? Key, int Value)> Map { get; }
 
-		public StringToInt(ILInstruction argument, List<(string? Key, int Value)> map)
+		public IType ExpectedType { get; }
+
+		public StringToInt(ILInstruction argument, List<(string? Key, int Value)> map, IType expectedType)
 			: base(OpCode.StringToInt)
 		{
 			this.Argument = argument;
 			this.Map = map;
+			this.ExpectedType = expectedType;
 		}
 
-		public StringToInt(ILInstruction argument, string?[] map)
-			: this(argument, ArrayToDictionary(map))
+		public StringToInt(ILInstruction argument, string?[] map, IType expectedType)
+			: this(argument, ArrayToDictionary(map), expectedType)
 		{
 		}
 
@@ -51,7 +56,9 @@ namespace ICSharpCode.Decompiler.IL
 		public override void WriteTo(ITextOutput output, ILAstWritingOptions options)
 		{
 			WriteILRange(output, options);
-			output.Write("string.to.int (");
+			output.Write("string.to.int ");
+			ExpectedType.WriteTo(output);
+			output.Write('(');
 			Argument.WriteTo(output, options);
 			output.Write(", { ");
 			int i = 0;

ICSharpCode.Decompiler/IL/Transforms/SwitchOnStringTransform.cs

@@ -78,7 +78,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 						changed = true;
 						continue;
 					}
-					if (MatchRoslynSwitchOnStringUsingLengthAndChar(block.Instructions, ref i))
+					if (MatchRoslynSwitchOnStringUsingLengthAndChar(block, i))
 					{
 						changed = true;
 						continue;
@@ -334,7 +334,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			int offset = firstBlock == null ? 1 : 0;
 			var sections = new List<SwitchSection>(values.Skip(offset).SelectWithIndex((index, s) => new SwitchSection { Labels = new LongSet(index), Body = s.Item2 is Block b ? new Branch(b) : s.Item2.Clone() }));
 			sections.Add(new SwitchSection { Labels = new LongSet(new LongInterval(0, sections.Count)).Invert(), Body = currentCaseBlock != null ? (ILInstruction)new Branch(currentCaseBlock) : new Leave((BlockContainer)nextCaseBlock) });
-			var stringToInt = new StringToInt(switchValue, values.Skip(offset).Select(item => item.Item1).ToArray());
+			var stringToInt = new StringToInt(switchValue, values.Skip(offset).Select(item => item.Item1).ToArray(), context.TypeSystem.FindType(KnownTypeCode.String));
 			var inst = new SwitchInstruction(stringToInt);
 			inst.Sections.AddRange(sections);
 			if (removeExtraLoad)
@@ -450,7 +450,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 
 			var sections = new List<SwitchSection>(values.SelectWithIndex((index, b) => new SwitchSection { Labels = new LongSet(index), Body = b.Item2 }));
 			sections.Add(new SwitchSection { Labels = new LongSet(new LongInterval(0, sections.Count)).Invert(), Body = new Branch(currentCaseBlock) });
-			var stringToInt = new StringToInt(switchValue, values.SelectArray(item => item.Item1));
+			var stringToInt = new StringToInt(switchValue, values.SelectArray(item => item.Item1), context.TypeSystem.FindType(KnownTypeCode.String));
 			var inst = new SwitchInstruction(stringToInt);
 			inst.Sections.AddRange(sections);
 
@@ -671,7 +671,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				switchValue = new LdLoc(switchValueVar);
 				keepAssignmentBefore = true;
 			}
-			var stringToInt = new StringToInt(switchValue, stringValues);
+			var stringToInt = new StringToInt(switchValue, stringValues, switchValueVar.Type);
 			var inst = new SwitchInstruction(stringToInt);
 			inst.Sections.AddRange(sections);
 			instructions[i + 1].ReplaceWith(inst);
@@ -860,7 +860,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			// stloc tmp(ldloc switch-value)
 			// stloc switchVariable(ldloc tmp)
 			// if (comp(ldloc tmp == ldnull)) br nullCaseBlock
-			// br getItemBloc
+			// br getItemBlock
 			if (block.Instructions.Count != i + 4)
 				return false;
 			if (!block.Instructions[i].MatchStLoc(out var tmp, out var switchValue))
@@ -919,7 +919,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				}
 			}
 			context.Step(nameof(MatchLegacySwitchOnStringWithHashtable), block.Instructions[i]);
-			var stringToInt = new StringToInt(switchValue, stringValues);
+			var stringToInt = new StringToInt(switchValue, stringValues, context.TypeSystem.FindType(KnownTypeCode.String));
 			var inst = new SwitchInstruction(stringToInt);
 			inst.Sections.AddRange(sections);
 			inst.AddILRange(block.Instructions[i]);
@@ -998,15 +998,20 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				switchBlockInstructions = nextBlockJump.TargetBlock.Instructions;
 				switchBlockInstructionsOffset = 0;
 			}
-			// stloc switchValueVar(call ComputeStringHash(switchValue))
+			// stloc switchValueVar(call ComputeStringHash(switchValueLoad))
 			// switch (ldloc switchValueVar) {
 			// 	case [211455823..211455824): br caseBlock1
 			//  ... more cases ...
 			// 	case [long.MinValue..-365098645),...,[1697255802..long.MaxValue]: br defaultBlock
 			// }
-			if (!(switchBlockInstructionsOffset + 1 < switchBlockInstructions.Count && switchBlockInstructions[switchBlockInstructionsOffset + 1] is SwitchInstruction switchInst && switchInst.Value.MatchLdLoc(out var switchValueVar) &&
-				MatchComputeStringHashCall(switchBlockInstructions[switchBlockInstructionsOffset], switchValueVar, out LdLoc switchValueLoad)))
+			if (!(switchBlockInstructionsOffset + 1 < switchBlockInstructions.Count
+				&& switchBlockInstructions[switchBlockInstructionsOffset + 1] is SwitchInstruction switchInst
+				&& switchInst.Value.MatchLdLoc(out var switchValueVar)
+				&& MatchComputeStringHashCall(switchBlockInstructions[switchBlockInstructionsOffset],
+											  switchValueVar, out LdLoc switchValueLoad)))
+			{
 				return false;
+			}
 
 			if (instForNullCheck != null && !instForNullCheck.MatchLdLoc(switchValueLoad.Variable))
 			{
@@ -1137,7 +1142,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					var body = bodyInstruction is Block b ? new Branch(b) : bodyInstruction;
 					sections[idx] = new SwitchSection { Labels = new LongSet(idx), Body = body };
 				}
-				var newSwitch = new SwitchInstruction(new StringToInt(switchValueInst, values));
+				var newSwitch = new SwitchInstruction(new StringToInt(switchValueInst, values, switchValueLoad.Variable.Type));
 				newSwitch.Sections.AddRange(sections);
 				newSwitch.Sections.Add(new SwitchSection { Labels = defaultLabel, Body = defaultSection.Body });
 				instructions[offset].ReplaceWith(newSwitch);
@@ -1145,54 +1150,63 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			}
 		}
 
-		private bool MatchRoslynSwitchOnStringUsingLengthAndChar(InstructionCollection<ILInstruction> instructions, ref int i)
+		private bool MatchRoslynSwitchOnStringUsingLengthAndChar(Block block, int i)
 		{
+			var instructions = block.Instructions;
 			// implements https://github.com/dotnet/roslyn/pull/66081
-			if (i >= instructions.Count - 1)
-				return false;
 			// if (comp(ldloc switchValueVar == ldnull)) br nullCase
 			// br nextBlock
-			if (!instructions[i].MatchIfInstruction(out var condition, out var exitBlockJump)
-				|| !condition.MatchCompEqualsNull(out var ldloc)
-				|| ldloc is not LdLoc { Variable: var switchValueVar })
-				return false;
-			if (!instructions[i + 1].MatchBranch(out var defaultCase))
-				return false;
-			if (!exitBlockJump.MatchBranch(out var nullCase))
-				return false;
-			// if (comp(ldloc switchValueVar == ldnull)) br defaultCase
-			// br switchOnLengthBlock
 			Block switchOnLengthBlock;
-			if (defaultCase.IncomingEdgeCount == 1
-				&& defaultCase.Instructions[0].MatchIfInstruction(out condition, out exitBlockJump)
-				&& condition.MatchCompEqualsNull(out ldloc)
-				&& ldloc.MatchLdLoc(switchValueVar))
+			int switchOnLengthBlockStartOffset;
+			Block nullCase = null;
+			if (instructions[i].MatchIfInstruction(out var condition, out var exitBlockJump)
+				&& condition.MatchCompEqualsNull(out var ldloc)
+				&& ldloc is LdLoc { Variable: var switchValueVar })
 			{
-				if (!defaultCase.Instructions[1].MatchBranch(out switchOnLengthBlock))
+				if (!instructions[i + 1].MatchBranch(out var nextBlock))
+					return false;
+				if (!exitBlockJump.MatchBranch(out nullCase))
 					return false;
-				if (!exitBlockJump.MatchBranch(out defaultCase))
+				// if (comp(ldloc switchValueVar == ldnull)) br ...
+				// br switchOnLengthBlock
+				if (nextBlock.IncomingEdgeCount == 1
+					&& nextBlock.Instructions[0].MatchIfInstruction(out condition, out _)
+					&& condition.MatchCompEqualsNull(out ldloc)
+					&& ldloc.MatchLdLoc(switchValueVar))
+				{
+					if (!nextBlock.Instructions[1].MatchBranch(out switchOnLengthBlock))
+						return false;
+				}
+				else
+				{
+					switchOnLengthBlock = nextBlock;
+				}
+				if (switchOnLengthBlock.IncomingEdgeCount != 1)
 					return false;
+				switchOnLengthBlockStartOffset = 0;
 			}
 			else
 			{
-				switchOnLengthBlock = defaultCase;
-				defaultCase = nullCase;
+				switchOnLengthBlock = block;
+				switchValueVar = null; // will be extracted in MatchSwitchOnLengthBlock
+				switchOnLengthBlockStartOffset = i;
 			}
-			if (!MatchSwitchOnLengthBlock(switchValueVar, switchOnLengthBlock, out var blocksByLength))
+			Block defaultCase = null;
+			if (!MatchSwitchOnLengthBlock(ref switchValueVar, switchOnLengthBlock, switchOnLengthBlockStartOffset, out var blocksByLength))
 				return false;
 			List<(string, ILInstruction)> stringValues = new();
-			foreach (var block in blocksByLength)
+			foreach (var b in blocksByLength)
 			{
-				if (block.Length.Count() != 1)
+				if (b.Length.Count() != 1)
 				{
-					if (block.TargetBlock != nullCase)
+					if (b.TargetBlock != nullCase)
 						return false;
 				}
 				else
 				{
-					int length = (int)block.Length.Intervals[0].Start;
-					if (MatchSwitchOnCharBlock(block.TargetBlock, length, switchValueVar, out var mapping)
-						|| MatchIfElseOnCharBlock(block.TargetBlock, length, switchValueVar, out mapping))
+					int length = (int)b.Length.Intervals[0].Start;
+					if (MatchSwitchOnCharBlock(b.TargetBlock, length, switchValueVar, out var mapping)
+						|| MatchIfElseOnCharBlock(b.TargetBlock, length, switchValueVar, out mapping))
 					{
 						foreach (var item in mapping)
 						{
@@ -1206,9 +1220,9 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 							}
 						}
 					}
-					else if (MatchRoslynCaseBlockHead(block.TargetBlock, switchValueVar, out var bodyOrLeave, out var exit, out string stringValue, out _))
+					else if (MatchRoslynCaseBlockHead(b.TargetBlock, switchValueVar, out var bodyOrLeave, out var exit, out string stringValue, out _))
 					{
-						if (exit != nullCase)
+						if (exit != defaultCase)
 							return false;
 						if (!stringValues.Any(x => x.Item1 == stringValue))
 						{
@@ -1221,7 +1235,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					}
 					else if (length == 0)
 					{
-						stringValues.Add(("", block.TargetBlock));
+						stringValues.Add(("", b.TargetBlock));
 					}
 					else
 					{
@@ -1236,7 +1250,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				{
 					stringValues.Add((null, nullBlock));
 				}
-				else if (nullCase != defaultCase)
+				else if (nullCase != null && nullCase != defaultCase)
 				{
 					stringValues.Add((null, nullCase));
 				}
@@ -1252,23 +1266,38 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				var body = bodyInstruction is Block b ? new Branch(b) : bodyInstruction;
 				sections[idx] = new SwitchSection { Labels = new LongSet(idx), Body = body };
 			}
-			var newSwitch = new SwitchInstruction(new StringToInt(new LdLoc(switchValueVar), values));
+			var newSwitch = new SwitchInstruction(new StringToInt(new LdLoc(switchValueVar), values, switchValueVar.Type));
 			newSwitch.Sections.AddRange(sections);
 			newSwitch.Sections.Add(new SwitchSection { Labels = defaultLabel, Body = new Branch(defaultCase) });
 			newSwitch.AddILRange(instructions[i]);
-			newSwitch.AddILRange(instructions[i + 1]);
-			instructions[i].ReplaceWith(newSwitch);
-			instructions.RemoveAt(i + 1);
+			if (nullCase != null)
+			{
+				newSwitch.AddILRange(instructions[i + 1]);
+			}
+			instructions[i] = newSwitch;
+			instructions.RemoveRange(i + 1, instructions.Count - (i + 1));
 			return true;
 
 			bool MatchGetChars(ILInstruction instruction, ILVariable switchValueVar, out int index)
 			{
 				index = -1;
-				return instruction is Call call
-					&& call.Method.FullNameIs("System.String", "get_Chars")
-					&& call.Arguments.Count == 2
-					&& call.Arguments[0].MatchLdLoc(switchValueVar)
-					&& call.Arguments[1].MatchLdcI4(out index);
+				if (context.Settings.SwitchOnReadOnlySpanChar && instruction.MatchLdObj(out var target, out var type) && type.IsKnownType(KnownTypeCode.UInt16))
+				{
+					return target is Call call
+						&& (call.Method.FullNameIs("System.ReadOnlySpan", "get_Item")
+						|| call.Method.FullNameIs("System.Span", "get_Item"))
+						&& call.Arguments.Count == 2
+						&& call.Arguments[0].MatchLdLoca(switchValueVar)
+						&& call.Arguments[1].MatchLdcI4(out index);
+				}
+				else
+				{
+					return instruction is Call call
+						&& call.Method.FullNameIs("System.String", "get_Chars")
+						&& call.Arguments.Count == 2
+						&& call.Arguments[0].MatchLdLoc(switchValueVar)
+						&& call.Arguments[1].MatchLdcI4(out index);
+				}
 			}
 
 			bool MatchSwitchOnCharBlock(Block block, int length, ILVariable switchValueVar, out List<(string StringValue, ILInstruction BodyOrLeave)> results)
@@ -1375,7 +1404,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 						break;
 					if (!MatchRoslynCaseBlockHead(headBlock, switchValueVar, out var bodyOrLeave, out var exit, out var stringValue, out _))
 						break;
-					if (exit != nullCase)
+					if (exit != defaultCase)
 						return false;
 					results ??= new();
 					results.Add((stringValue, bodyOrLeave));
@@ -1385,28 +1414,24 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				return true;
 			}
 
-			bool MatchSwitchOnLengthBlock(ILVariable switchValueVar, Block switchOnLengthBlock, out List<(LongSet Length, Block TargetBlock)> blocks)
+			bool MatchSwitchOnLengthBlock(ref ILVariable switchValueVar, Block switchOnLengthBlock, int startOffset, out List<(LongSet Length, Block TargetBlock)> blocks)
 			{
 				blocks = null;
-				if (switchOnLengthBlock.IncomingEdgeCount != 1)
-					return false;
 				SwitchInstruction @switch;
 				ILInstruction getLengthCall;
 				ILVariable lengthVar;
-				if (switchOnLengthBlock.FinalInstruction is not Nop)
-					return false;
-				switch (switchOnLengthBlock.Instructions.Count)
+				switch (switchOnLengthBlock.Instructions.Count - startOffset)
 				{
 					case 1:
-						@switch = switchOnLengthBlock.Instructions[0] as SwitchInstruction;
+						@switch = switchOnLengthBlock.Instructions[startOffset] as SwitchInstruction;
 						if (@switch == null)
 							return false;
 						getLengthCall = @switch.Value;
 						break;
 					case 2:
-						if (!switchOnLengthBlock.Instructions[0].MatchStLoc(out lengthVar, out getLengthCall))
+						if (!switchOnLengthBlock.Instructions[startOffset].MatchStLoc(out lengthVar, out getLengthCall))
 							return false;
-						@switch = switchOnLengthBlock.Instructions[1] as SwitchInstruction;
+						@switch = switchOnLengthBlock.Instructions[startOffset + 1] as SwitchInstruction;
 						if (@switch == null)
 							return false;
 						if (!@switch.Value.MatchLdLoc(lengthVar))
@@ -1414,13 +1439,13 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 						break;
 					case 3:
 						@switch = null;
-						if (!switchOnLengthBlock.Instructions[0].MatchStLoc(out lengthVar, out getLengthCall))
+						if (!switchOnLengthBlock.Instructions[startOffset].MatchStLoc(out lengthVar, out getLengthCall))
 							return false;
-						if (!switchOnLengthBlock.Instructions[1].MatchIfInstruction(out var cond, out var gotoLength))
+						if (!switchOnLengthBlock.Instructions[startOffset + 1].MatchIfInstruction(out var cond, out var gotoLength))
 							return false;
 						if (!gotoLength.MatchBranch(out var target))
 							return false;
-						if (!switchOnLengthBlock.Instructions[2].MatchBranch(out var gotoElse))
+						if (!switchOnLengthBlock.Instructions[startOffset + 2].MatchBranch(out var gotoElse))
 							return false;
 						if (!cond.MatchCompEquals(out var lhs, out var rhs))
 						{
@@ -1430,8 +1455,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 							target = gotoElse;
 							gotoElse = t;
 						}
-						if (gotoElse != defaultCase)
-							return false;
+						defaultCase = gotoElse;
 						if (!lhs.MatchLdLoc(lengthVar) || !rhs.MatchLdcI4(out int length))
 							return false;
 
@@ -1445,12 +1469,27 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				}
 				if (getLengthCall is not Call call
 					|| call.Arguments.Count != 1
-					|| !call.Method.FullNameIs("System.String", "get_Length"))
+					|| call.Method.Name != "get_Length")
 				{
 					return false;
 				}
-				if (!call.Arguments[0].MatchLdLoc(switchValueVar))
-					return false;
+				var declaringTypeCode = call.Method.DeclaringTypeDefinition?.KnownTypeCode;
+				switch (declaringTypeCode)
+				{
+					case KnownTypeCode.String:
+						if (!call.Arguments[0].MatchLdLoc(switchValueVar))
+							return false;
+						break;
+					case KnownTypeCode.ReadOnlySpanOfT:
+					case KnownTypeCode.SpanOfT:
+						if (!context.Settings.SwitchOnReadOnlySpanChar)
+							return false;
+						if (!call.Arguments[0].MatchLdLoca(out switchValueVar))
+							return false;
+						break;
+					default:
+						return false;
+				}
 				if (@switch == null)
 					return true;
 				blocks = new(@switch.Sections.Count);
@@ -1462,7 +1501,8 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 						return false;
 					if (section.Labels.Count() != 1)
 					{
-						if (!section.Body.MatchBranch(defaultCase))
+						defaultCase ??= target;
+						if (defaultCase != target)
 							return false;
 					}
 					else
@@ -1644,8 +1684,9 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		}
 
 		/// <summary>
-		/// Matches 'call string.op_Equality(ldloc(variable), ldstr(stringValue))'
+		/// Matches 'call string.op_Equality(ldloc(variable), ldstr stringValue)'
 		///      or 'comp(ldloc(variable) == ldnull)'
+		///      or 'call SequenceEqual(ldloc variable, call AsSpan(ldstr stringValue))'
 		/// </summary>
 		bool MatchStringEqualityComparison(ILInstruction condition, ILVariable variable, out string stringValue, out bool isVBCompareString)
 		{
@@ -1653,8 +1694,9 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		}
 
 		/// <summary>
-		/// Matches 'call string.op_Equality(ldloc(variable), ldstr(stringValue))'
+		/// Matches 'call string.op_Equality(ldloc(variable), ldstr stringValue)'
 		///      or 'comp(ldloc(variable) == ldnull)'
+		///      or 'call SequenceEqual(ldloc variable, call AsSpan(ldstr stringValue))'
 		/// </summary>
 		bool MatchStringEqualityComparison(ILInstruction condition, out ILVariable variable, out string stringValue, out bool isVBCompareString)
 		{
@@ -1676,8 +1718,8 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					right = c.Arguments[1];
 				}
 				else if (c.Method.IsStatic && c.Method.Name == "CompareString"
-				  && c.Method.DeclaringType.FullName == "Microsoft.VisualBasic.CompilerServices.Operators"
-				  && c.Arguments.Count == 3)
+					&& c.Method.DeclaringType.FullName == "Microsoft.VisualBasic.CompilerServices.Operators"
+					&& c.Arguments.Count == 3)
 				{
 					left = c.Arguments[0];
 					right = c.Arguments[1];
@@ -1690,6 +1732,25 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 						return false;
 					}
 				}
+				else if (c.Method.IsStatic && c.Method.Name == "SequenceEqual"
+					&& c.Method.DeclaringType.FullName == "System.MemoryExtensions"
+					&& c.Arguments.Count == 2)
+				{
+					left = c.Arguments[0];
+					if (c.Arguments[1] is Call {
+						Method.IsStatic: true,
+						Method.Name: "AsSpan",
+						Method.DeclaringType.FullName: "System.MemoryExtensions",
+						Arguments: [var ldStr]
+					} asSpanCall)
+					{
+						right = ldStr;
+					}
+					else
+					{
+						return false;
+					}
+				}
 				else
 				{
 					return false;

ILSpy/Properties/Resources.Designer.cs

@@ -1316,6 +1316,15 @@ namespace ICSharpCode.ILSpy.Properties {
             }
         }
         
+        /// <summary>
+        ///   Looks up a localized string similar to Use switch on (ReadOnly)Span&lt;char&gt;.
+        /// </summary>
+        public static string DecompilerSettings_SwitchOnReadOnlySpanChar {
+            get {
+                return ResourceManager.GetString("DecompilerSettings.SwitchOnReadOnlySpanChar", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Looks up a localized string similar to Unsigned right shift (&gt;&gt;&gt;).
         /// </summary>

ILSpy/Properties/Resources.resx

@@ -462,6 +462,9 @@ Are you sure you want to continue?</value>
   <data name="DecompilerSettings.SwitchExpressions" xml:space="preserve">
     <value>Switch expressions</value>
   </data>
+  <data name="DecompilerSettings.SwitchOnReadOnlySpanChar" xml:space="preserve">
+    <value>Use switch on (ReadOnly)Span&lt;char&gt;</value>
+  </data>
   <data name="DecompilerSettings.UnsignedRightShift" xml:space="preserve">
     <value>Unsigned right shift (&gt;&gt;&gt;)</value>
   </data>