Fix #2527: Support skip locals init

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -2444,9 +2444,9 @@ namespace ICSharpCode.Decompiler.CSharp
 				var body = statementBuilder.ConvertAsBlock(container);
 				var comment = new Comment(" Could not convert BlockContainer to single expression");
 				body.InsertChildAfter(null, comment, Roles.Comment);
-				// set ILVariable.HasInitialValue for any variables being used inside the container
+				// set ILVariable.UsesInitialValue for any variables being used inside the container
 				foreach (var stloc in container.Descendants.OfType<StLoc>())
-					stloc.Variable.HasInitialValue = true;
+					stloc.Variable.UsesInitialValue = true;
 				var ame = new AnonymousMethodExpression { Body = body };
 				var systemFuncType = compilation.FindType(typeof(Func<>));
 				var blockReturnType = InferReturnType(body);

ICSharpCode.Decompiler/CSharp/Transforms/DeclareVariables.cs

@@ -70,6 +70,13 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			}
 		}
 
+		enum VariableInitKind
+		{
+			None,
+			NeedsDefaultValue,
+			NeedsSkipInit
+		}
+
 		[DebuggerDisplay("VariableToDeclare(Name={Name})")]
 		class VariableToDeclare
 		{
@@ -80,7 +87,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			/// <summary>
 			/// Whether the variable needs to be default-initialized.
 			/// </summary>
-			public bool DefaultInitialization;
+			public VariableInitKind DefaultInitialization;
 
 			/// <summary>
 			/// Integer value that can be used to compare to VariableToDeclare instances
@@ -106,10 +113,24 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			public bool RemovedDueToCollision => ReplacementDueToCollision != null;
 			public bool DeclaredInDeconstruction;
 
-			public VariableToDeclare(ILVariable variable, bool defaultInitialization, InsertionPoint insertionPoint, IdentifierExpression firstUse, int sourceOrder)
+			public VariableToDeclare(ILVariable variable, InsertionPoint insertionPoint, IdentifierExpression firstUse, int sourceOrder)
 			{
 				this.ILVariable = variable;
-				this.DefaultInitialization = defaultInitialization;
+				if (variable.UsesInitialValue)
+				{
+					if (variable.InitialValueIsInitialized)
+					{
+						this.DefaultInitialization = VariableInitKind.NeedsDefaultValue;
+					}
+					else
+					{
+						this.DefaultInitialization = VariableInitKind.NeedsSkipInit;
+					}
+				}
+				else
+				{
+					this.DefaultInitialization = VariableInitKind.None;
+				}
 				this.InsertionPoint = insertionPoint;
 				this.FirstUse = firstUse;
 				this.SourceOrder = sourceOrder;
@@ -304,7 +325,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 						else
 						{
 							newPoint = new InsertionPoint { level = nodeLevel, nextNode = identExpr };
-							if (variable.HasInitialValue)
+							if (variable.UsesInitialValue)
 							{
 								// Uninitialized variables are logically initialized at the beginning of the function
 								// Because it's possible that the variable has a loop-carried dependency,
@@ -331,8 +352,8 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 						}
 						else
 						{
-							v = new VariableToDeclare(variable, variable.HasInitialValue,
-								newPoint, identExpr, sourceOrder: variableDict.Count);
+							v = new VariableToDeclare(variable, newPoint,
+								identExpr, sourceOrder: variableDict.Count);
 							variableDict.Add(variable, v);
 						}
 					}
@@ -623,17 +644,69 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 					// Insert a separate declaration statement.
 					Expression initializer = null;
 					AstType type = context.TypeSystemAstBuilder.ConvertType(v.Type);
-					if (v.DefaultInitialization)
+					if (v.DefaultInitialization == VariableInitKind.NeedsDefaultValue)
 					{
 						initializer = new DefaultValueExpression(type.Clone());
 					}
 					var vds = new VariableDeclarationStatement(type, v.Name, initializer);
 					vds.Variables.Single().AddAnnotation(new ILVariableResolveResult(ilVariable));
 					Debug.Assert(v.InsertionPoint.nextNode.Role == BlockStatement.StatementRole);
-					v.InsertionPoint.nextNode.Parent.InsertChildBefore(
-						v.InsertionPoint.nextNode,
-						vds,
-						BlockStatement.StatementRole);
+					if (v.DefaultInitialization == VariableInitKind.NeedsSkipInit)
+					{
+						AstType unsafeType = context.TypeSystemAstBuilder.ConvertType(
+							context.TypeSystem.FindType(KnownTypeCode.Unsafe));
+						if (context.Settings.OutVariables)
+						{
+							var outVarDecl = new OutVarDeclarationExpression(type.Clone(), v.Name);
+							outVarDecl.Variable.AddAnnotation(new ILVariableResolveResult(ilVariable));
+							v.InsertionPoint.nextNode.Parent.InsertChildBefore(
+								v.InsertionPoint.nextNode,
+								new ExpressionStatement {
+									Expression = new InvocationExpression {
+										Target = new MemberReferenceExpression {
+											Target = new TypeReferenceExpression(unsafeType),
+											MemberName = "SkipInit"
+										},
+										Arguments = {
+											outVarDecl
+										}
+									}
+								},
+								BlockStatement.StatementRole);
+						}
+						else
+						{
+							v.InsertionPoint.nextNode.Parent.InsertChildBefore(
+								v.InsertionPoint.nextNode,
+								vds,
+								BlockStatement.StatementRole);
+							v.InsertionPoint.nextNode.Parent.InsertChildBefore(
+								v.InsertionPoint.nextNode,
+								new ExpressionStatement {
+									Expression = new InvocationExpression {
+										Target = new MemberReferenceExpression {
+											Target = new TypeReferenceExpression(unsafeType),
+											MemberName = "SkipInit"
+										},
+										Arguments = {
+											new DirectionExpression(
+												FieldDirection.Out,
+												new IdentifierExpression(v.Name)
+													.WithRR(new ILVariableResolveResult(ilVariable))
+											)
+										}
+									}
+								},
+								BlockStatement.StatementRole);
+						}
+					}
+					else
+					{
+						v.InsertionPoint.nextNode.Parent.InsertChildBefore(
+							v.InsertionPoint.nextNode,
+							vds,
+							BlockStatement.StatementRole);
+					}
 				}
 			}
 			// perform replacements at end, so that we don't replace a node while it is still referenced by a VariableToDeclare
@@ -650,7 +723,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 				return false;
 			if (!context.Settings.OutVariables)
 				return false;
-			if (v.DefaultInitialization)
+			if (v.DefaultInitialization != VariableInitKind.None)
 				return false;
 			for (AstNode node = v.FirstUse; node != null; node = node.Parent)
 			{

ICSharpCode.Decompiler/FlowAnalysis/ReachingDefinitionsVisitor.cs

@@ -296,14 +296,9 @@ namespace ICSharpCode.Decompiler.FlowAnalysis
 				var stores = storesByVar[vi];
 				if (stores != null)
 				{
-					int expectedStoreCount = scope.Variables[vi].StoreCount;
-					if (!scope.Variables[vi].HasInitialValue)
-					{
-						// Extra store for the uninitialized state.
-						expectedStoreCount += 1;
-						// Note that for variables with HasInitialValue=true,
-						// this extra store is already accounted for in ILVariable.StoreCount.
-					}
+					int expectedStoreCount = scope.Variables[vi].StoreInstructions.Count;
+					// Extra store for the uninitialized state.
+					expectedStoreCount += 1;
 					Debug.Assert(stores.Count == expectedStoreCount);
 					stores.CopyTo(allStores, si);
 					// Add all stores except for the first (representing the uninitialized state)

ICSharpCode.Decompiler/IL/ControlFlow/YieldReturnDecompiler.cs

@@ -995,7 +995,8 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 							name = fieldDef.Name.Substring(1, pos - 1);
 					}
 					v = function.RegisterVariable(VariableKind.Local, ldflda.Field.ReturnType, name);
-					v.HasInitialValue = true; // the field was default-initialized, so keep those semantics for the variable
+					v.InitialValueIsInitialized = true; // the field was default-initialized, so keep those semantics for the variable
+					v.UsesInitialValue = true;
 					v.StateMachineField = ldflda.Field;
 					fieldToVariableMap.Add(fieldDef, v);
 				}

ICSharpCode.Decompiler/IL/ILReader.cs

@@ -118,12 +118,10 @@ namespace ICSharpCode.Decompiler.IL
 			this.methodReturnStackType = method.ReturnType.GetStackType();
 			InitParameterVariables();
 			localVariables = InitLocalVariables();
-			if (body.LocalVariablesInitialized)
+			foreach (var v in localVariables)
 			{
-				foreach (var v in localVariables)
-				{
-					v.HasInitialValue = true;
-				}
+				v.InitialValueIsInitialized = body.LocalVariablesInitialized;
+				v.UsesInitialValue = true;
 			}
 			this.mainContainer = new BlockContainer(expectedResultType: methodReturnStackType);
 			this.instructionBuilder = new List<ILInstruction>();

ICSharpCode.Decompiler/IL/ILVariable.cs

@@ -252,13 +252,13 @@ namespace ICSharpCode.Decompiler.IL
 		/// <item>stloc</item>
 		/// <item>TryCatchHandler (assigning the exception variable)</item>
 		/// <item>PinnedRegion (assigning the pointer variable)</item>
-		/// <item>initial values (<see cref="HasInitialValue"/>)</item>
+		/// <item>initial values (<see cref="UsesInitialValue"/>)</item>
 		/// </list>
 		/// </summary>
 		/// <remarks>
 		/// This variable is automatically updated when adding/removing stores instructions from the ILAst.
 		/// </remarks>
-		public int StoreCount => (hasInitialValue ? 1 : 0) + StoreInstructions.Count;
+		public int StoreCount => (usesInitialValue ? 1 : 0) + StoreInstructions.Count;
 
 		readonly List<IStoreInstruction> storeInstructions = new List<IStoreInstruction>();
 
@@ -270,7 +270,7 @@ namespace ICSharpCode.Decompiler.IL
 		/// <item>stloc</item>
 		/// <item>TryCatchHandler (assigning the exception variable)</item>
 		/// <item>PinnedRegion (assigning the pointer variable)</item>
-		/// <item>initial values (<see cref="HasInitialValue"/>) -- however, there is no instruction for
+		/// <item>initial values (<see cref="UsesInitialValue"/>) -- however, there is no instruction for
 		///       the initial value, so it is not contained in the store list.</item>
 		/// </list>
 		/// </summary>
@@ -320,27 +320,86 @@ namespace ICSharpCode.Decompiler.IL
 			list.RemoveAt(indexToMove);
 		}
 
-		bool hasInitialValue;
+		bool initialValueIsInitialized;
 
 		/// <summary>
-		/// Gets/Sets whether the variable has an initial value.
+		/// Gets/Sets whether the variable's initial value is initialized.
 		/// This is always <c>true</c> for parameters (incl. <c>this</c>).
 		/// 
-		/// Normal variables have an initial value if the function uses ".locals init"
-		/// and that initialization is not a dead store.
+		/// Normal variables have an initial value if the function uses ".locals init".
+		/// </summary>
+		public bool InitialValueIsInitialized {
+			get { return initialValueIsInitialized; }
+			set {
+				if (Kind == VariableKind.Parameter && !value)
+					throw new InvalidOperationException("Cannot remove InitialValueIsInitialized from parameters");
+				initialValueIsInitialized = value;
+			}
+		}
+
+		bool usesInitialValue;
+
+		/// <summary>
+		/// Gets/Sets whether the initial value of the variable is used.
+		/// This is always <c>true</c> for parameters (incl. <c>this</c>).
+		/// 
+		/// Normal variables use the initial value, if no explicit initialization is done.
 		/// </summary>
 		/// <remarks>
-		/// An initial value is counted as a store (adds 1 to StoreCount)
+		/// The following table shows the relationship between <see cref="InitialValueIsInitialized"/>
+		/// and <see cref="UsesInitialValue"/>.
+		/// <list type="table">
+		/// <listheader>
+		/// <term><see cref="InitialValueIsInitialized"/></term>
+		/// <term><see cref="UsesInitialValue"/></term>
+		/// <term>Meaning</term>
+		/// </listheader>
+		/// <item>
+		/// <term><see langword="true" /></term>
+		/// <term><see langword="true" /></term>
+		/// <term>This variable's initial value is zero-initialized (<c>.locals init</c>) and the initial value is used.
+		/// From C#'s point of view a the value <c>default(T)</c> is assigned at the site of declaration.</term>
+		/// </item>
+		/// <item>
+		/// <term><see langword="true" /></term>
+		/// <term><see langword="false" /></term>
+		/// <term>This variable's initial value is zero-initialized (<c>.locals init</c>) and the initial value is not used.
+		/// From C#'s point of view no implicit initialization occurs, because the code assigns a value
+		/// explicitly, before the variable is first read.</term>
+		/// </item>
+		/// <item>
+		/// <term><see langword="false" /></term>
+		/// <term><see langword="true" /></term>
+		/// <term>This variable's initial value is uninitialized (<c>.locals</c> without <c>init</c>) and the
+		/// initial value is used.
+		/// From C#'s point of view a call to <see cref="System.Runtime.CompilerServices.Unsafe.SkipInit{T}(out T)"/>
+		/// is generated after the declaration.</term>
+		/// </item>
+		/// <item>
+		/// <term><see langword="false" /></term>
+		/// <term><see langword="false" /></term>
+		/// <term>This variable's initial value is uninitialized (<c>.locals</c> without <c>init</c>) and the
+		/// initial value is not used.
+		/// From C#'s point of view no implicit initialization occurs, because the code assigns a value
+		/// explicitly, before the variable is first read.</term>
+		/// </item>
+		/// </list>
 		/// </remarks>
-		public bool HasInitialValue {
-			get { return hasInitialValue; }
+		public bool UsesInitialValue {
+			get { return usesInitialValue; }
 			set {
 				if (Kind == VariableKind.Parameter && !value)
-					throw new InvalidOperationException("Cannot remove HasInitialValue from parameters");
-				hasInitialValue = value;
+					throw new InvalidOperationException("Cannot remove UsesInitialValue from parameters");
+				usesInitialValue = value;
 			}
 		}
 
+		[Obsolete("Use 'UsesInitialValue' instead.")]
+		public bool HasInitialValue {
+			get => UsesInitialValue;
+			set => UsesInitialValue = value;
+		}
+
 		/// <summary>
 		/// Gets whether the variable is in SSA form:
 		/// There is exactly 1 store, and every load sees the value from that store.
@@ -362,7 +421,7 @@ namespace ICSharpCode.Decompiler.IL
 		/// </summary>
 		public bool IsDead {
 			get {
-				return StoreCount == (HasInitialValue ? 1 : 0)
+				return StoreInstructions.Count == 0
 					&& LoadCount == 0
 					&& AddressCount == 0;
 			}
@@ -388,7 +447,10 @@ namespace ICSharpCode.Decompiler.IL
 			this.StackType = type.GetStackType();
 			this.Index = index;
 			if (kind == VariableKind.Parameter)
-				this.HasInitialValue = true;
+			{
+				this.InitialValueIsInitialized = true;
+				this.UsesInitialValue = true;
+			}
 			CheckInvariant();
 		}
 
@@ -401,7 +463,10 @@ namespace ICSharpCode.Decompiler.IL
 			this.StackType = stackType;
 			this.Index = index;
 			if (kind == VariableKind.Parameter)
-				this.HasInitialValue = true;
+			{
+				this.InitialValueIsInitialized = true;
+				this.UsesInitialValue = true;
+			}
 			CheckInvariant();
 		}
 
@@ -472,9 +537,24 @@ namespace ICSharpCode.Decompiler.IL
 				output.Write("Index={0}, ", Index);
 			}
 			output.Write("LoadCount={0}, AddressCount={1}, StoreCount={2})", LoadCount, AddressCount, StoreCount);
-			if (hasInitialValue && Kind != VariableKind.Parameter)
+			if (Kind != VariableKind.Parameter)
 			{
-				output.Write(" init");
+				if (initialValueIsInitialized)
+				{
+					output.Write(" init");
+				}
+				else
+				{
+					output.Write(" uninit");
+				}
+				if (usesInitialValue)
+				{
+					output.Write(" used");
+				}
+				else
+				{
+					output.Write(" unused");
+				}
 			}
 			if (CaptureScope != null)
 			{

ICSharpCode.Decompiler/IL/Transforms/RemoveDeadVariableInit.cs

@@ -36,7 +36,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 	{
 		public void Run(ILFunction function, ILTransformContext context)
 		{
-			ResetHasInitialValueFlag(function, context);
+			ResetUsesInitialValueFlag(function, context);
 			// Remove dead stores to variables that are never read from.
 			// If the stored value has some side-effect, the value is unwrapped.
 			// This is necessary to remove useless stores generated by some compilers, e.g., the F# compiler.
@@ -105,7 +105,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			}
 		}
 
-		internal static void ResetHasInitialValueFlag(ILFunction function, ILTransformContext context)
+		internal static void ResetUsesInitialValueFlag(ILFunction function, ILTransformContext context)
 		{
 			var visitor = new DefiniteAssignmentVisitor(function, context.CancellationToken);
 			function.AcceptVisitor(visitor);
@@ -113,7 +113,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			{
 				if (v.Kind != VariableKind.Parameter && !visitor.IsPotentiallyUsedUninitialized(v))
 				{
-					v.HasInitialValue = false;
+					v.UsesInitialValue = false;
 				}
 			}
 		}

ICSharpCode.Decompiler/IL/Transforms/SplitVariables.cs

@@ -270,14 +270,15 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					v.Name = inst.Variable.Name;
 					v.HasGeneratedName = inst.Variable.HasGeneratedName;
 					v.StateMachineField = inst.Variable.StateMachineField;
-					v.HasInitialValue = false; // we'll set HasInitialValue when we encounter an uninit load
+					v.InitialValueIsInitialized = inst.Variable.InitialValueIsInitialized;
+					v.UsesInitialValue = false; // we'll set UsesInitialValue when we encounter an uninit load
 					v.RemoveIfRedundant = inst.Variable.RemoveIfRedundant;
 					newVariables.Add(representative, v);
 					inst.Variable.Function.Variables.Add(v);
 				}
-				if (inst.Variable.HasInitialValue && uninitVariableUsage.TryGetValue(inst.Variable, out var uninitLoad) && uninitLoad == inst)
+				if (inst.Variable.UsesInitialValue && uninitVariableUsage.TryGetValue(inst.Variable, out var uninitLoad) && uninitLoad == inst)
 				{
-					v.HasInitialValue = true;
+					v.UsesInitialValue = true;
 				}
 				return v;
 			}

ICSharpCode.Decompiler/IL/Transforms/TransformDisplayClassUsage.cs

@@ -56,7 +56,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			public string Name => field.Name;
 
 			public bool CanPropagate { get; private set; }
-			public bool HasInitialValue { get; set; }
+			public bool UsesInitialValue { get; set; }
 
 			public HashSet<ILInstruction> Initializers { get; } = new HashSet<ILInstruction>();
 
@@ -80,7 +80,8 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				if (declaredVariable != null)
 					return declaredVariable;
 				declaredVariable = container.Variable.Function.RegisterVariable(VariableKind.Local, field.Type, field.Name);
-				declaredVariable.HasInitialValue = HasInitialValue;
+				declaredVariable.InitialValueIsInitialized = true;
+				declaredVariable.UsesInitialValue = UsesInitialValue;
 				declaredVariable.CaptureScope = container.CaptureScope;
 				return declaredVariable;
 			}
@@ -185,7 +186,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					if (displayClass.VariablesToDeclare.ContainsKey(f))
 						continue;
 					var variable = AddVariable(displayClass, null, f);
-					variable.HasInitialValue = true;
+					variable.UsesInitialValue = true;
 					displayClass.VariablesToDeclare[(IField)f.MemberDefinition] = variable;
 				}
 
@@ -304,7 +305,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					HandleInitBlock(stloc.Parent as Block, stloc.ChildIndex + 1, result, result.Variable);
 					break;
 				case TypeKind.Struct:
-					if (v.StoreCount != (v.HasInitialValue ? 1 : 0))
+					if (v.StoreInstructions.Count != 0)
 						return null;
 					Debug.Assert(v.StoreInstructions.Count == 0);
 					result = new DisplayClass(v, definition) { CaptureScope = v.CaptureScope };
@@ -509,8 +510,8 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				variable.Propagate(ResolveVariableToPropagate(statement.Value, field.Type));
 				variable.Initializers.Add(statement);
 			}
-			variable.HasInitialValue =
-				result.Type.IsReferenceType != false || result.Variable.HasInitialValue;
+			variable.UsesInitialValue =
+				result.Type.IsReferenceType != false || result.Variable.UsesInitialValue;
 			return variable;
 		}
 
@@ -583,7 +584,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			context.Step($"ResetHasInitialValueFlag", function);
 			foreach (var f in function.Descendants.OfType<ILFunction>())
 			{
-				RemoveDeadVariableInit.ResetHasInitialValueFlag(f, context);
+				RemoveDeadVariableInit.ResetUsesInitialValueFlag(f, context);
 				f.CapturedVariables.RemoveWhere(v => v.IsDead);
 			}
 		}
@@ -601,7 +602,8 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				}
 			}
 			closureType = variable.Type.GetDefinition();
-			if (context.Settings.LocalFunctions && closureType?.Kind == TypeKind.Struct && variable.HasInitialValue && IsPotentialClosure(context, closureType))
+			if (context.Settings.LocalFunctions && closureType?.Kind == TypeKind.Struct
+				&& variable.UsesInitialValue && IsPotentialClosure(context, closureType))
 			{
 				initializer = LocalFunctionDecompiler.GetStatement(variable.AddressInstructions.OrderBy(i => i.StartILOffset).First());
 				return true;