Fix #1193: Performance issues with deeply nested block structures

ICSharpCode.Decompiler/IL/ControlFlow/ConditionDetection.cs

@@ -125,8 +125,10 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			context.Step("Inline block as then-branch", ifInst.TrueInst);
 			// The targetBlock was already processed, and is ready to embed
 			var targetBlock = ((Branch)ifInst.TrueInst).TargetBlock;
+			targetBlock.AddRef();  // Peformance: avoid temporarily disconnecting targetBlock
 			targetBlock.Remove();
 			ifInst.TrueInst = targetBlock;
+			targetBlock.ReleaseRef();
 
 			return true;
 		}
@@ -430,8 +432,10 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 
 			context.Step("Swap then-branch with else-branch to match IL order", ifInst);
 			var oldTrue = ifInst.TrueInst;
+			oldTrue.AddRef(); // Peformance: avoid temporarily disconnecting oldTrue
 			ifInst.TrueInst = ifInst.FalseInst;
 			ifInst.FalseInst = oldTrue;
+			oldTrue.ReleaseRef();
 			ifInst.Condition = Comp.LogicNot(ifInst.Condition);
 		}
 
@@ -599,14 +603,9 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 
 			// continue blocks have exactly 2 incoming edges
 			if (currentContainer.EntryPoint.IncomingEdgeCount == 2) {
-				try {
-					var forIncrement = HighLevelLoopTransform.GetIncrementBlock(currentContainer, currentContainer.EntryPoint);
-					if (forIncrement != null)
-						return forIncrement;
-				} catch (InvalidOperationException) {
-					// multiple potential increment blocks. Can get this because we don't check that the while loop
-					// has a condition first, as we don't need to do too much of HighLevelLoopTransform's job.
-				}
+				var forIncrement = HighLevelLoopTransform.GetIncrementBlock(currentContainer, currentContainer.EntryPoint);
+				if (forIncrement != null)
+					return forIncrement;
 			}
 
 			return currentContainer.EntryPoint;

ICSharpCode.Decompiler/IL/Transforms/DelegateConstruction.cs

@@ -40,26 +40,25 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			var orphanedVariableInits = new List<ILInstruction>();
 			var targetsToReplace = new List<IInstructionWithVariableOperand>();
 			var translatedDisplayClasses = new HashSet<ITypeDefinition>();
-			foreach (var block in function.Descendants.OfType<Block>()) {
-				for (int i = block.Instructions.Count - 1; i >= 0; i--) {
-					context.CancellationToken.ThrowIfCancellationRequested();
-					foreach (var call in block.Instructions[i].Descendants.OfType<NewObj>()) {
-						ILFunction f = TransformDelegateConstruction(call, out ILInstruction target);
-						if (f != null) {
-							call.ReplaceWith(f);
-							if (target is IInstructionWithVariableOperand && !target.MatchLdThis())
-								targetsToReplace.Add((IInstructionWithVariableOperand)target);
-						}
+			var cancellationToken = context.CancellationToken;
+			foreach (var inst in function.Descendants) {
+				cancellationToken.ThrowIfCancellationRequested();
+				if (inst is NewObj call) {
+					ILFunction f = TransformDelegateConstruction(call, out ILInstruction target);
+					if (f != null) {
+						call.ReplaceWith(f);
+						if (target is IInstructionWithVariableOperand && !target.MatchLdThis())
+							targetsToReplace.Add((IInstructionWithVariableOperand)target);
 					}
-					if (block.Instructions[i].MatchStLoc(out ILVariable targetVariable, out ILInstruction value)) {
-						var newObj = value as NewObj;
-						// TODO : it is probably not a good idea to remove *all* display-classes
-						// is there a way to minimize the false-positives?
-						if (newObj != null && IsInSimpleDisplayClass(newObj.Method)) {
-							targetVariable.CaptureScope = BlockContainer.FindClosestContainer(block);
-							targetsToReplace.Add((IInstructionWithVariableOperand)block.Instructions[i]);
-							translatedDisplayClasses.Add(newObj.Method.DeclaringTypeDefinition);
-						}
+				}
+				if (inst.MatchStLoc(out ILVariable targetVariable, out ILInstruction value)) {
+					var newObj = value as NewObj;
+					// TODO : it is probably not a good idea to remove *all* display-classes
+					// is there a way to minimize the false-positives?
+					if (newObj != null && IsInSimpleDisplayClass(newObj.Method)) {
+						targetVariable.CaptureScope = BlockContainer.FindClosestContainer(inst);
+						targetsToReplace.Add((IInstructionWithVariableOperand)inst);
+						translatedDisplayClasses.Add(newObj.Method.DeclaringTypeDefinition);
 					}
 				}
 			}

ICSharpCode.Decompiler/IL/Transforms/TransformExpressionTrees.cs

@@ -130,6 +130,8 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				}
 				return false;
 			}
+			if (instruction is Block block && block.Kind == BlockKind.ControlFlow)
+				return false;  // don't look into nested blocks
 			foreach (var child in instruction.Children) {
 				if (TryConvertExpressionTree(child, statement))
 					return true;