Add some missing checks to MatchRoslynSwitchOnString

ICSharpCode.Decompiler/IL/ControlFlow/ControlFlowSimplification.cs

@@ -51,7 +51,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 				InlineVariableInReturnBlock(block, context);
 				// 1st pass SimplifySwitchInstruction before SimplifyBranchChains()
 				// starts duplicating return instructions.
-				SwitchDetection.SimplifySwitchInstruction(block);
+				SwitchDetection.SimplifySwitchInstruction(block, context);
 			}
 			SimplifyBranchChains(function, context);
 			CleanUpEmptyBlocks(function, context);

ICSharpCode.Decompiler/IL/ControlFlow/SwitchDetection.cs

@@ -24,6 +24,7 @@ using System.Diagnostics;
 using ICSharpCode.Decompiler.FlowAnalysis;
 using ICSharpCode.Decompiler.Util;
 using ICSharpCode.Decompiler.TypeSystem;
+using ICSharpCode.Decompiler.CSharp.Transforms;
 
 namespace ICSharpCode.Decompiler.IL.ControlFlow
 {
@@ -198,11 +199,11 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			} else {
 				// 2nd pass of SimplifySwitchInstruction (after duplicating return blocks),
 				// (1st pass was in ControlFlowSimplification)
-				SimplifySwitchInstruction(block);
+				SimplifySwitchInstruction(block, context);
 			}
 		}
 
-		internal static void SimplifySwitchInstruction(Block block)
+		internal static void SimplifySwitchInstruction(Block block, ILTransformContext context)
 		{
 			// due to our of of basic blocks at this point,
 			// switch instructions can only appear as last insturction
@@ -228,7 +229,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 					}
 					return false;
 				});
-			AdjustLabels(sw);
+			AdjustLabels(sw, context);
 			SortSwitchSections(sw);
 		}
 
@@ -237,10 +238,11 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			sw.Sections.ReplaceList(sw.Sections.OrderBy(s => (s.Body as Branch)?.TargetILOffset).ThenBy(s => s.Labels.Values.FirstOrDefault()));
 		}
 
-		static void AdjustLabels(SwitchInstruction sw)
+		static void AdjustLabels(SwitchInstruction sw, ILTransformContext context)
 		{
 			if (sw.Value is BinaryNumericInstruction bop && !bop.CheckForOverflow && bop.Right.MatchLdcI(out long val)) {
 				// Move offset into labels:
+				context.Step("Move offset into switch labels", bop);
 				long offset;
 				switch (bop.Operator) {
 					case BinaryNumericOperator.Add:

ICSharpCode.Decompiler/IL/Transforms/SwitchOnNullableTransform.cs

@@ -59,7 +59,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					}
 				}
 				if (!changed) continue;
-				SwitchDetection.SimplifySwitchInstruction(block);
+				SwitchDetection.SimplifySwitchInstruction(block, context);
 				if (block.Parent is BlockContainer container)
 					changedContainers.Add(container);
 			}

ICSharpCode.Decompiler/IL/Transforms/SwitchOnStringTransform.cs

@@ -33,13 +33,16 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 	/// </summary>
 	class SwitchOnStringTransform : IILTransform
 	{
+		ILTransformContext context;
+
 		public void Run(ILFunction function, ILTransformContext context)
 		{
 			if (!context.Settings.SwitchStatementOnString)
 				return;
 
+			this.context = context;
 			BlockContainer body = (BlockContainer)function.Body;
-			var hashtableInitializers = ScanHashtableInitializerBlocks(body.EntryPoint); 
+			var hashtableInitializers = ScanHashtableInitializerBlocks(body.EntryPoint);
 
 			HashSet<BlockContainer> changedContainers = new HashSet<BlockContainer>();
 
@@ -70,7 +73,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					}
 				}
 				if (!changed) continue;
-				SwitchDetection.SimplifySwitchInstruction(block);
+				SwitchDetection.SimplifySwitchInstruction(block, context);
 				if (block.Parent is BlockContainer container)
 					changedContainers.Add(container);
 			}
@@ -83,6 +86,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				if (!transformed) continue;
 				if (!omittedBlocks.TryGetValue(previous, out var actual))
 					actual = previous;
+				context.Step("Remove hashtable initializer", actual);
 				if (jumpToNext != null) {
 					actual.Instructions.SecondToLastOrDefault().ReplaceWith(jumpToNext);
 				}
@@ -95,6 +99,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			if (hashtableInitializers.Count > 0 && omittedBlocks.Count == hashtableInitializers.Count && body.EntryPoint.Instructions.Count == 2) {
 				if (body.EntryPoint.Instructions[0] is IfInstruction ifInst
 					&& ifInst.TrueInst.MatchBranch(out var beginOfMethod) && body.EntryPoint.Instructions[1].MatchBranch(beginOfMethod)) {
+					context.Step("Remove initial null check", body);
 					body.EntryPoint.Instructions.RemoveAt(0);
 				}
 			}
@@ -345,7 +350,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			var stringToInt = new StringToInt(switchValue, values.SelectArray(item => item.Item1));
 			var inst = new SwitchInstruction(stringToInt);
 			inst.Sections.AddRange(sections);
-			
+
 			inst.AddILRange(instructions[i - 1]);
 			instructions[i].ReplaceWith(inst);
 			instructions.RemoveAt(i + 1);
@@ -828,9 +833,9 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			InstructionCollection<ILInstruction> switchBlockInstructions = instructions;
 			int switchBlockInstructionsOffset = i;
 			Block nullValueCaseBlock = null;
+			ILInstruction instForNullCheck = null;
 			if (instructions[i].MatchIfInstruction(out var condition, out var exitBlockJump)
-				&& condition.MatchCompEquals(out var left, out var right) && right.MatchLdNull())
-			{
+				&& condition.MatchCompEqualsNull(out instForNullCheck)) {
 				var nextBlockJump = instructions[i + 1] as Branch;
 				if (nextBlockJump == null || nextBlockJump.TargetBlock.IncomingEdgeCount != 1)
 					return false;
@@ -849,9 +854,14 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				MatchComputeStringHashCall(switchBlockInstructions[switchBlockInstructionsOffset], switchValueVar, out LdLoc switchValueLoad)))
 				return false;
 
+			if (instForNullCheck != null && !instForNullCheck.MatchLdLoc(switchValueLoad.Variable)) {
+				return false;
+			}
+
 			var stringValues = new List<(string Value, ILInstruction TargetBlockOrLeave)>();
 			SwitchSection defaultSection = switchInst.Sections.MaxBy(s => s.Labels.Count());
-			Block exitOrDefaultBlock = null;
+			if (!defaultSection.Body.MatchBranch(out Block exitOrDefaultBlock))
+				return false;
 			foreach (var section in switchInst.Sections) {
 				if (section == defaultSection) continue;
 				// extract target block
@@ -866,9 +876,8 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					return false;
 				}
 
-				if (exitOrDefaultBlock != null && exitOrDefaultBlock != currentExitBlock)
+				if (currentExitBlock != exitOrDefaultBlock)
 					return false;
-				exitOrDefaultBlock = currentExitBlock;
 				if (emptyStringEqualsNull && string.IsNullOrEmpty(stringValue)) {
 					stringValues.Add((null, targetOrLeave));
 					stringValues.Add((string.Empty, targetOrLeave));
@@ -881,6 +890,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				stringValues.Add((null, nullValueCaseBlock));
 			}
 
+			context.Step(nameof(MatchRoslynSwitchOnString), switchValueLoad);
 			ILInstruction switchValueInst = switchValueLoad;
 			if (instructions == switchBlockInstructions) {
 				// stloc switchValueLoadVariable(switchValue)