Implement foreach loop detection in StatementBuilder.

ICSharpCode.Decompiler/CSharp/StatementBuilder.cs

@@ -26,6 +26,8 @@ using ICSharpCode.Decompiler.TypeSystem;
 using ICSharpCode.Decompiler.Util;
 using System;
 using System.Threading;
+using ICSharpCode.Decompiler.IL.Transforms;
+using ICSharpCode.Decompiler.CSharp.Syntax.PatternMatching;
 
 namespace ICSharpCode.Decompiler.CSharp
 {
@@ -254,14 +256,75 @@ namespace ICSharpCode.Decompiler.CSharp
 			};
 		}
 
+		#region foreach construction
+		static readonly AssignmentExpression getEnumeratorPattern = new AssignmentExpression(new NamedNode("enumerator", new IdentifierExpression(Pattern.AnyString)), new InvocationExpression(new MemberReferenceExpression(new AnyNode("collection").ToExpression(), "GetEnumerator")));
+		static readonly InvocationExpression moveNextConditionPattern = new InvocationExpression(new MemberReferenceExpression(new NamedNode("enumerator", new IdentifierExpression(Pattern.AnyString)), "MoveNext"));
+
 		protected internal override Statement VisitUsingInstruction(UsingInstruction inst)
 		{
+			var resource = exprBuilder.Translate(inst.ResourceExpression);
+			var m = getEnumeratorPattern.Match(resource.Expression);
+			if (inst.Body is BlockContainer container && m.Success) {
+				var enumeratorVar = m.Get<IdentifierExpression>("enumerator").Single().GetILVariable();
+				var loop = DetectedLoop.DetectLoop(container);
+				if (loop.Kind == LoopKind.While && loop.Body is Block body) {
+					var condition = exprBuilder.TranslateCondition(loop.Conditions.Single());
+					var m2 = moveNextConditionPattern.Match(condition.Expression);
+					if (m2.Success) {
+						var enumeratorVar2 = m2.Get<IdentifierExpression>("enumerator").Single().GetILVariable();
+						if (enumeratorVar2 == enumeratorVar && BodyHasSingleGetCurrent(body, enumeratorVar, condition.ILInstructions.Single(),
+							out var singleGetter, out var needsUninlining, out var itemVariable)) {
+							var collectionExpr = m.Get<Expression>("collection").Single().Detach();
+							if (needsUninlining) {
+								itemVariable = currentFunction.RegisterVariable(
+									VariableKind.ForeachLocal, singleGetter.Method.ReturnType,
+									AssignVariableNames.GenerateVariableName(currentFunction, collectionExpr.Annotation<ILInstruction>(), "item")
+								);
+								singleGetter.ReplaceWith(new LdLoc(itemVariable));
+								body.Instructions.Insert(0, new StLoc(itemVariable, singleGetter));
+							} else {
+								itemVariable.Kind = VariableKind.ForeachLocal;
+								itemVariable.Name = AssignVariableNames.GenerateVariableName(currentFunction, collectionExpr.Annotation<ILInstruction>(), "item", itemVariable);
+							}
+							var whileLoop = (WhileStatement)ConvertAsBlock(inst.Body).Single();
+							BlockStatement foreachBody = (BlockStatement)whileLoop.EmbeddedStatement.Detach();
+							foreachBody.Statements.First().Detach();
+							return new ForeachStatement {
+								VariableType = exprBuilder.ConvertType(itemVariable.Type),
+								VariableName = itemVariable.Name,
+								InExpression = collectionExpr,
+								EmbeddedStatement = foreachBody
+							};
+						}
+					}
+				}
+			}
 			return new UsingStatement {
-				ResourceAcquisition = exprBuilder.Translate(inst.ResourceExpression),
+				ResourceAcquisition = resource,
 				EmbeddedStatement = ConvertAsBlock(inst.Body)
 			};
 		}
 
+		bool BodyHasSingleGetCurrent(Block body, ILVariable enumerator, ILInstruction moveNextUsage, out CallInstruction singleGetter, out bool needsUninlining, out ILVariable existingVariable)
+		{
+			singleGetter = null;
+			needsUninlining = false;
+			existingVariable = null;
+			var loads = (enumerator.LoadInstructions.OfType<ILInstruction>().Concat(enumerator.AddressInstructions.OfType<ILInstruction>())).Where(ld => !ld.IsDescendantOf(moveNextUsage)).ToArray();
+			if (loads.Length == 1 && ParentIsCurrentGetter(loads[0])) {
+				singleGetter = (CallInstruction)loads[0].Parent;
+				needsUninlining = !singleGetter.Parent.MatchStLoc(out existingVariable);
+			}
+			return singleGetter != null && singleGetter.IsDescendantOf(body.Instructions[0]) && ILInlining.CanUninline(singleGetter, body.Instructions[0]);
+		}
+
+		bool ParentIsCurrentGetter(ILInstruction inst)
+		{
+			return inst.Parent is CallVirt cv && cv.Method.IsAccessor &&
+				cv.Method.AccessorOwner is IProperty p && p.Getter.Equals(cv.Method);
+		}
+		#endregion
+
 		protected internal override Statement VisitPinnedRegion(PinnedRegion inst)
 		{
 			var fixedStmt = new FixedStatement();

ICSharpCode.Decompiler/IL/DetectedLoop.cs

@@ -118,12 +118,10 @@ namespace ICSharpCode.Decompiler.IL
 						Kind = LoopKind.For;
 						IncrementTarget = variable;
 						AdditionalBlocks = Container.Blocks.Skip(1).ToArray();
-					} else {
+						return this;
-						AdditionalBlocks = Container.Blocks.Skip(1).ToArray();
 					}
-				} else {
-					AdditionalBlocks = Container.Blocks.Skip(1).ToArray();
 				}
+				AdditionalBlocks = Container.Blocks.Skip(1).ToArray();
 			} else {
 				// do-while or while(true)-loop
 				if (Container.EntryPoint.IncomingEdgeCount == 2) {

ICSharpCode.Decompiler/IL/Instructions/ILFunction.cs

@@ -148,6 +148,7 @@ namespace ICSharpCode.Decompiler.IL
 			if (string.IsNullOrWhiteSpace(name)) {
 				switch (kind) {
 					case VariableKind.Local:
+					case VariableKind.ForeachLocal:
 						name = "V_";
 						break;
 					case VariableKind.Parameter:

ICSharpCode.Decompiler/IL/Transforms/AssignVariableNames.cs

@@ -61,7 +61,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			reservedVariableNames = new Dictionary<string, int>();
 			loopCounters = CollectLoopCounters(function);
 			foreach (var p in function.Descendants.OfType<ILFunction>().Select(f => f.Method).SelectMany(m => m.Parameters))
-				AddExistingName(p.Name);
+				AddExistingName(reservedVariableNames, p.Name);
 			foreach (ILFunction f in function.Descendants.OfType<ILFunction>().Reverse()) {
 				PerformAssignment(f);
 			}
@@ -76,7 +76,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					case VariableKind.Parameter: // ignore
 						break;
 					case VariableKind.InitializerTarget: // keep generated names
-						AddExistingName(v.Name);
+						AddExistingName(reservedVariableNames, v.Name);
 						break;
 					default:
 						if (v.HasGeneratedName || !IsValidName(v.Name)) {
@@ -96,7 +96,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				var v = inst.Variable;
 				if (!mapping.TryGetValue(v, out string name)) {
 					if (string.IsNullOrEmpty(v.Name))
-						v.Name = GenerateNameForVariable(v, function.Body);
+						v.Name = GenerateNameForVariable(v);
 					mapping.Add(v, v.Name);
 				} else {
 					v.Name = name;
@@ -128,8 +128,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				}
 			}
 
-			int number;
+			string nameWithoutDigits = SplitName(oldVariableName, out int number);
-			string nameWithoutDigits = SplitName(oldVariableName, out number);
 
 			if (!reservedVariableNames.ContainsKey(nameWithoutDigits)) {
 				reservedVariableNames.Add(nameWithoutDigits, number - 1);
@@ -156,7 +155,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return loopCounters;
 		}
 
-		string GenerateNameForVariable(ILVariable variable, ILInstruction methodBody)
+		string GenerateNameForVariable(ILVariable variable)
 		{
 			string proposedName = null;
 			if (variable.Type.IsKnownType(KnownTypeCode.Int32)) {
@@ -192,8 +191,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			}
 
 			// remove any numbers from the proposed name
-			int number;
+			proposedName = SplitName(proposedName, out int number);
-			proposedName = SplitName(proposedName, out number);
 
 			if (!reservedVariableNames.ContainsKey(proposedName)) {
 				reservedVariableNames.Add(proposedName, 0);
@@ -291,7 +289,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return name;
 		}
 
-		void AddExistingName(string name)
+		static void AddExistingName(Dictionary<string, int> reservedVariableNames, string name)
 		{
 			if (string.IsNullOrEmpty(name))
 				return;
@@ -336,5 +334,34 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			else
 				return char.ToLower(name[0]) + name.Substring(1);
 		}
+
+		internal static string GenerateVariableName(ILFunction currentFunction, ILInstruction valueContext, string fallback, ILVariable existingVariable = null)
+		{
+			if (currentFunction == null)
+				throw new ArgumentNullException(nameof(currentFunction));
+			var reservedVariableNames = new Dictionary<string, int>();
+			foreach (var v in currentFunction.Descendants.OfType<ILFunction>().SelectMany(m => m.Variables)) {
+				if (v != existingVariable)
+					AddExistingName(reservedVariableNames, v.Name);
+			}
+			var proposedName = GetNameFromInstruction(valueContext);
+
+			if (string.IsNullOrEmpty(proposedName)) {
+				proposedName = fallback;
+			}
+
+			// remove any numbers from the proposed name
+			proposedName = SplitName(proposedName, out int number);
+
+			if (!reservedVariableNames.ContainsKey(proposedName)) {
+				reservedVariableNames.Add(proposedName, 0);
+			}
+			int count = ++reservedVariableNames[proposedName];
+			if (count > 1) {
+				return proposedName + count.ToString();
+			} else {
+				return proposedName;
+			}
+		}
 	}
 }

ICSharpCode.Decompiler/IL/Transforms/ILInlining.cs

@@ -306,7 +306,27 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			ILInstruction loadInst;
 			return FindLoadInNext(expr, v, expressionBeingMoved, out loadInst) == true;
 		}
-		
+
+		/// <summary>
+		/// Gets whether arg can be un-inlined out of stmt.
+		/// </summary>
+		internal static bool CanUninline(ILInstruction arg, ILInstruction stmt)
+		{
+			Debug.Assert(arg.IsDescendantOf(stmt));
+			for (ILInstruction inst = arg; inst != stmt; inst = inst.Parent) {
+				if (!inst.SlotInfo.CanInlineInto)
+					return false;
+				// Check whether re-ordering with predecessors is valid:
+				int childIndex = inst.ChildIndex;
+				for (int i = 0; i < childIndex; ++i) {
+					ILInstruction predecessor = inst.Parent.Children[i];
+					if (!SemanticHelper.MayReorder(arg, predecessor))
+						return false;
+				}
+			}
+			return true;
+		}
+
 		/// <summary>
 		/// Finds the position to inline to.
 		/// </summary>