Improve yield-return-decompiler.

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -127,10 +127,10 @@ namespace ICSharpCode.Decompiler.CSharp
 			return cexpr;
 		}
 		
-		public TranslatedExpression TranslateCondition(ILInstruction condition)
+		public TranslatedExpression TranslateCondition(ILInstruction condition, bool negate = false)
 		{
 			var expr = Translate(condition, compilation.FindType(KnownTypeCode.Boolean));
-			return expr.ConvertToBoolean(this);
+			return expr.ConvertToBoolean(this, negate);
 		}
 		
 		ExpressionWithResolveResult ConvertVariable(ILVariable variable)
@@ -322,7 +322,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		
 		protected internal override TranslatedExpression VisitLogicNot(LogicNot inst, TranslationContext context)
 		{
-			return LogicNot(TranslateCondition(inst.Argument)).WithILInstruction(inst);
+			return TranslateCondition(inst.Argument, negate: true).WithILInstruction(inst);
 		}
 		
 		protected internal override TranslatedExpression VisitBitNot(BitNot inst, TranslationContext context)
@@ -362,7 +362,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				.WithILInstruction(inst);
 		}
 		
-		ExpressionWithResolveResult LogicNot(TranslatedExpression expr)
+		internal ExpressionWithResolveResult LogicNot(TranslatedExpression expr)
 		{
 			return new UnaryOperatorExpression(UnaryOperatorType.Not, expr.Expression)
 				.WithRR(new OperatorResolveResult(compilation.FindType(KnownTypeCode.Boolean), ExpressionType.Not, expr.ResolveResult));

ICSharpCode.Decompiler/CSharp/TranslatedExpression.cs

@@ -311,21 +311,29 @@ namespace ICSharpCode.Decompiler.CSharp
 		/// 
 		/// Expects that the input expression is an integer expression; produces an expression
 		/// that returns <c>true</c> iff the integer value is not 0.
+		/// 
+		/// If negate is true, instead produces an expression that returns <c>true</c> iff the integer value is 0.
 		/// </summary>
-		public TranslatedExpression ConvertToBoolean(ExpressionBuilder expressionBuilder)
+		public TranslatedExpression ConvertToBoolean(ExpressionBuilder expressionBuilder, bool negate = false)
 		{
 			if (Type.IsKnownType(KnownTypeCode.Boolean) || Type.Kind == TypeKind.Unknown) {
-				return this;
+				if (negate) {
+					return expressionBuilder.LogicNot(this).WithoutILInstruction();
+				} else {
+					return this;
+				}
 			}
 			Debug.Assert(Type.GetStackType().IsIntegerType());
 			IType boolType = expressionBuilder.compilation.FindType(KnownTypeCode.Boolean);
 			if (ResolveResult.IsCompileTimeConstant && ResolveResult.ConstantValue is int) {
 				bool val = (int)ResolveResult.ConstantValue != 0;
+				val ^= negate;
 				return new PrimitiveExpression(val)
 					.WithILInstruction(this.ILInstructions)
 					.WithRR(new ConstantResolveResult(boolType, val));
 			} else if (ResolveResult.IsCompileTimeConstant && ResolveResult.ConstantValue is byte) {
 				bool val = (byte)ResolveResult.ConstantValue != 0;
+				val ^= negate;
 				return new PrimitiveExpression(val)
 					.WithILInstruction(this.ILInstructions)
 					.WithRR(new ConstantResolveResult(boolType, val));
@@ -333,7 +341,8 @@ namespace ICSharpCode.Decompiler.CSharp
 				var nullRef = new NullReferenceExpression()
 					.WithoutILInstruction()
 					.WithRR(new ConstantResolveResult(SpecialType.NullType, null));
-				return new BinaryOperatorExpression(Expression, BinaryOperatorType.InEquality, nullRef.Expression)
+				var op = negate ? BinaryOperatorType.Equality : BinaryOperatorType.InEquality;
+				return new BinaryOperatorExpression(Expression, op, nullRef.Expression)
 					.WithoutILInstruction()
 					.WithRR(new OperatorResolveResult(boolType, System.Linq.Expressions.ExpressionType.NotEqual,
 					                                  this.ResolveResult, nullRef.ResolveResult));
@@ -341,7 +350,8 @@ namespace ICSharpCode.Decompiler.CSharp
 				var zero = new PrimitiveExpression(0)
 					.WithoutILInstruction()
 					.WithRR(new ConstantResolveResult(expressionBuilder.compilation.FindType(KnownTypeCode.Int32), 0));
-				return new BinaryOperatorExpression(Expression, BinaryOperatorType.InEquality, zero.Expression)
+				var op = negate ? BinaryOperatorType.Equality : BinaryOperatorType.InEquality;
+				return new BinaryOperatorExpression(Expression, op, zero.Expression)
 					.WithoutILInstruction()
 					.WithRR(new OperatorResolveResult(boolType, System.Linq.Expressions.ExpressionType.NotEqual,
 					                                  this.ResolveResult, zero.ResolveResult));

ICSharpCode.Decompiler/IL/ControlFlow/YieldReturnDecompiler.cs

@@ -134,6 +134,12 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			DecompileFinallyBlocks();
 			ReconstructTryFinallyBlocks(newBody);
 
+			// Copy-propagate temporaries holding a copy of 'this'.
+			// This is necessary because the old (pre-Roslyn) C# compiler likes to store 'this' in temporary variables.
+			foreach (var stloc in function.Descendants.OfType<StLoc>().Where(s => s.Variable.IsSingleDefinition && s.Value.MatchLdThis()).ToList()) {
+				CopyPropagation.Propagate(stloc, context);
+			}
+
 			context.Step("Translate fields to local accesses", function);
 			TranslateFieldsToLocalAccess(function, function, fieldToParameterMap);
 
@@ -141,6 +147,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 				context.Step("Remove temporaries", function);
 				foreach (var store in returnStores) {
 					if (store.Variable.LoadCount == 0 && store.Variable.AddressCount == 0 && store.Parent is Block block) {
+						Debug.Assert(SemanticHelper.IsPure(store.Value.Flags));
 						block.Instructions.Remove(store);
 					}
 				}
@@ -589,15 +596,27 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 							name = fieldDef.Name.Substring(1, pos - 1);
 					}
 					v = function.RegisterVariable(VariableKind.Local, ldflda.Field.ReturnType, name);
+					v.StateMachineField = ldflda.Field;
 					fieldToVariableMap.Add(fieldDef, v);
 				}
-				inst.ReplaceWith(new LdLoca(v));
+				inst.ReplaceWith(new LdLoca(v) { ILRange = inst.ILRange });
 			} else if (inst.MatchLdThis()) {
-				inst.ReplaceWith(new InvalidExpression("iterator") { ExpectedResultType = inst.ResultType });
+				inst.ReplaceWith(new InvalidExpression("stateMachine") { ExpectedResultType = inst.ResultType, ILRange = inst.ILRange });
 			} else {
 				foreach (var child in inst.Children) {
 					TranslateFieldsToLocalAccess(function, child, fieldToVariableMap);
 				}
+				if (inst is LdObj ldobj && ldobj.Target is LdLoca ldloca && ldloca.Variable.StateMachineField != null) {
+					LdLoc ldloc = new LdLoc(ldloca.Variable);
+					ldloc.AddILRange(ldobj.ILRange);
+					ldloc.AddILRange(ldloca.ILRange);
+					inst.ReplaceWith(ldloc);
+				} else if (inst is StObj stobj && stobj.Target is LdLoca ldloca2 && ldloca2.Variable.StateMachineField != null) {
+					StLoc stloc = new StLoc(ldloca2.Variable, stobj.Value);
+					stloc.AddILRange(stobj.ILRange);
+					stloc.AddILRange(ldloca2.ILRange);
+					inst.ReplaceWith(stloc);
+				}
 			}
 		}
 		#endregion

ICSharpCode.Decompiler/IL/ILVariable.cs

@@ -239,6 +239,12 @@ namespace ICSharpCode.Decompiler.IL
 				return StoreCount == 1 && AddressCount == 0;
 			}
 		}
+
+		/// <summary>
+		/// The field which was converted to a local variable.
+		/// Set when the variable is from a 'yield return' or 'async' state machine.
+		/// </summary>
+		public IField StateMachineField;
 		
 		public ILVariable(VariableKind kind, IType type, int index)
 		{
@@ -302,6 +308,9 @@ namespace ICSharpCode.Decompiler.IL
 			if (CaptureScope != null) {
 				output.Write(" captured in " + CaptureScope.EntryPoint.Label);
 			}
+			if (StateMachineField != null) {
+				output.Write(" from state-machine");
+			}
 		}
 		
 		internal void WriteTo(ITextOutput output)

ICSharpCode.Decompiler/IL/Transforms/CopyPropagation.cs

@@ -18,6 +18,8 @@
 
 using ICSharpCode.Decompiler.TypeSystem;
 using ICSharpCode.Decompiler.Util;
+using System.Diagnostics;
+using System.Linq;
 
 namespace ICSharpCode.Decompiler.IL.Transforms
 {
@@ -31,6 +33,14 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 	/// </summary>
 	public class CopyPropagation : IBlockTransform
 	{
+		public static void Propagate(StLoc store, ILTransformContext context)
+		{
+			Debug.Assert(store.Variable.IsSingleDefinition);
+			Block block = (Block)store.Parent;
+			int i = store.ChildIndex;
+			DoPropagate(store.Variable, store.Value, block, ref i, context);
+		}
+
 		public void Run(Block block, BlockTransformContext context)
 		{
 			for (int i = 0; i < block.Instructions.Count; i++) {
@@ -38,31 +48,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				ILInstruction copiedExpr;
 				if (block.Instructions[i].MatchStLoc(out v, out copiedExpr)) {
 					if (v.IsSingleDefinition && CanPerformCopyPropagation(v, copiedExpr)) {
-						context.Step($"Copy propagate {v.Name}", copiedExpr);
-						// un-inline the arguments of the ldArg instruction
-						ILVariable[] uninlinedArgs = new ILVariable[copiedExpr.Children.Count];
-						for (int j = 0; j < uninlinedArgs.Length; j++) {
-							var arg = copiedExpr.Children[j];
-							var type = context.TypeSystem.Compilation.FindType(arg.ResultType.ToKnownTypeCode());
-							uninlinedArgs[j] = new ILVariable(VariableKind.StackSlot, type, arg.ResultType, arg.ILRange.Start) {
-								Name = "C_" + arg.ILRange.Start
-							};
-							block.Instructions.Insert(i++, new StLoc(uninlinedArgs[j], arg));
-						}
-						CollectionExtensions.AddRange(v.Function.Variables, uninlinedArgs);
-						// perform copy propagation:
-						foreach (var expr in v.Function.Descendants) {
-							if (expr.MatchLdLoc(v)) {
-								var clone = copiedExpr.Clone();
-								for (int j = 0; j < uninlinedArgs.Length; j++) {
-									clone.Children[j].ReplaceWith(new LdLoc(uninlinedArgs[j]));
-								}
-								expr.ReplaceWith(clone);
-							}
-						}
-						block.Instructions.RemoveAt(i);
-						int c = ILInlining.InlineInto(block, i, aggressive: false, context: context);
-						i -= c + 1;
+						DoPropagate(v, copiedExpr, block, ref i, context);
 					}
 				}
 			}
@@ -99,6 +85,33 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					return value.Flags == InstructionFlags.None && value.Children.Count == 0 && target.Kind == VariableKind.StackSlot;
 			}
 		}
+
+		static void DoPropagate(ILVariable v, ILInstruction copiedExpr, Block block, ref int i, ILTransformContext context)
+		{
+			context.Step($"Copy propagate {v.Name}", copiedExpr);
+			// un-inline the arguments of the ldArg instruction
+			ILVariable[] uninlinedArgs = new ILVariable[copiedExpr.Children.Count];
+			for (int j = 0; j < uninlinedArgs.Length; j++) {
+				var arg = copiedExpr.Children[j];
+				var type = context.TypeSystem.Compilation.FindType(arg.ResultType.ToKnownTypeCode());
+				uninlinedArgs[j] = new ILVariable(VariableKind.StackSlot, type, arg.ResultType, arg.ILRange.Start) {
+					Name = "C_" + arg.ILRange.Start
+				};
+				block.Instructions.Insert(i++, new StLoc(uninlinedArgs[j], arg));
+			}
+			CollectionExtensions.AddRange(v.Function.Variables, uninlinedArgs);
+			// perform copy propagation:
+			foreach (var expr in v.LoadInstructions.ToArray()) {
+				var clone = copiedExpr.Clone();
+				for (int j = 0; j < uninlinedArgs.Length; j++) {
+					clone.Children[j].ReplaceWith(new LdLoc(uninlinedArgs[j]));
+				}
+				expr.ReplaceWith(clone);
+			}
+			block.Instructions.RemoveAt(i);
+			int c = ILInlining.InlineInto(block, i, aggressive: false, context: context);
+			i -= c + 1;
+		}
 	}
 }
 

ICSharpCode.Decompiler/IL/Transforms/ExpressionTransforms.cs

@@ -224,6 +224,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			{
 				context.Step("stobj(ldloca(v), ...) => stloc(v, ...)", inst);
 				inst.ReplaceWith(new StLoc(v, inst.Value));
+				return;
 			}
 			
 			ILInstruction target;

ICSharpCode.Decompiler/IL/Transforms/ILInlining.cs

@@ -166,7 +166,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 						return false;
 				} else {
 					Debug.Assert(loadInst.OpCode == OpCode.LdLoc);
-					if (!aggressive && v.Kind != VariableKind.StackSlot && !NonAggressiveInlineInto(next, loadInst, inlinedExpression))
+					if (!aggressive && v.Kind != VariableKind.StackSlot && !NonAggressiveInlineInto(next, loadInst, inlinedExpression, v))
 						return false;
 				}
 
@@ -254,7 +254,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// <param name="next">The next top-level expression</param>
 		/// <param name="loadInst">The load within 'next'</param>
 		/// <param name="inlinedExpression">The expression being inlined</param>
-		static bool NonAggressiveInlineInto(ILInstruction next, ILInstruction loadInst, ILInstruction inlinedExpression)
+		static bool NonAggressiveInlineInto(ILInstruction next, ILInstruction loadInst, ILInstruction inlinedExpression, ILVariable v)
 		{
 			Debug.Assert(loadInst.IsDescendantOf(next));
 			
@@ -266,6 +266,13 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					return true;
 				case OpCode.CompoundAssignmentInstruction:
 					return true;
+				case OpCode.LdLoc:
+					if (v.StateMachineField == null && ((LdLoc)inlinedExpression).Variable.StateMachineField != null) {
+						// Roslyn likes to put the result of fetching a state machine field into a temporary variable,
+						// so inline more aggressively in such cases.
+						return true;
+					}
+					break;
 			}
 			
 			// decide based on the target into which we are inlining

ICSharpCode.Decompiler/IL/Transforms/SplitVariables.cs

@@ -96,6 +96,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				if (!newVariables.TryGetValue(representative, out v)) {
 					v = new ILVariable(inst.Variable.Kind, inst.Variable.Type, inst.Variable.StackType, inst.Variable.Index);
 					v.Name = inst.Variable.Name;
+					v.StateMachineField = inst.Variable.StateMachineField;
 					v.HasInitialValue = false; // we'll set HasInitialValue when we encounter an uninit load
 					newVariables.Add(representative, v);
 					inst.Variable.Function.Variables.Add(v);