[async] small improvements to await decompilation

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -1732,7 +1732,23 @@ namespace ICSharpCode.Decompiler.CSharp
 
 		protected internal override TranslatedExpression VisitAwait(Await inst, TranslationContext context)
 		{
-			var value = Translate(inst.Value);
+			IType expectedType = null;
+			if (inst.GetAwaiterMethod != null) {
+				if (inst.GetAwaiterMethod.IsStatic) {
+					expectedType = inst.GetAwaiterMethod.Parameters.FirstOrDefault()?.Type;
+				} else {
+					expectedType = inst.GetAwaiterMethod.DeclaringType;
+				}
+			}
+
+			var value = Translate(inst.Value, typeHint: expectedType);
+			if (value.Expression is DirectionExpression) {
+				// we can deference the managed reference by stripping away the 'ref'
+				value = value.UnwrapChild(((DirectionExpression)value.Expression).Expression);
+			}
+			if (expectedType != null) {
+				value = value.ConvertTo(expectedType, this, allowImplicitConversion: true);
+			}
 			return new UnaryOperatorExpression(UnaryOperatorType.Await, value.Expression)
 				.WithILInstruction(inst)
 				.WithRR(new ResolveResult(inst?.GetResultMethod.ReturnType ?? SpecialType.UnknownType));

ICSharpCode.Decompiler/IL/ControlFlow/AsyncAwaitDecompiler.cs

@@ -58,6 +58,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 		ILVariable doFinallyBodies;
 
 		// These fields are set by AnalyzeStateMachine():
+		int smallestAwaiterVarIndex;
 
 		// For each block containing an 'await', stores the awaiter variable, and the field storing the awaiter
 		// across the yield point.
@@ -90,6 +91,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			DetectAwaitPattern(function);
 
 			context.Step("Translate fields to local accesses", function);
+			MarkGeneratedVariables(function);
 			YieldReturnDecompiler.TranslateFieldsToLocalAccess(function, function, fieldToParameterMap);
 
 			FinalizeInlineMoveNext(function);
@@ -444,6 +446,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 		void AnalyzeStateMachine(ILFunction function)
 		{
 			context.Step("AnalyzeStateMachine()", function);
+			smallestAwaiterVarIndex = int.MaxValue;
 			foreach (var container in function.Descendants.OfType<BlockContainer>()) {
 				// Use a separate state range analysis per container.
 				var sra = new StateRangeAnalysis(StateRangeAnalysisMode.AsyncMoveNext, stateField, cachedStateVar);
@@ -464,6 +467,9 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 								block.Instructions.Add(new InvalidBranch("Could not find block for state " + state));
 							}
 							awaitBlocks.Add(block, (awaiterVar, awaiterField));
+							if (awaiterVar.Index < smallestAwaiterVarIndex) {
+								smallestAwaiterVarIndex = awaiterVar.Index;
+							}
 						}
 					}
 				}
@@ -731,5 +737,16 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			return block.Instructions[pos].MatchBranch(completedBlock);
 		}
 		#endregion
+
+		void MarkGeneratedVariables(ILFunction function)
+		{
+			// Variables after the awaiters are usually compiler-generated;
+			// so mark them as stack slots.
+			foreach (var v in function.Variables) {
+				if (v.Kind == VariableKind.Local && v.Index >= smallestAwaiterVarIndex) {
+					v.Kind = VariableKind.StackSlot;
+				}
+			}
+		}
 	}
 }

ICSharpCode.Decompiler/IL/Transforms/ILInlining.cs

@@ -240,8 +240,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					case OpCode.CallVirt:
 						return !((CallVirt)parent).Method.IsStatic;
 					case OpCode.LdFlda:
-					// TODO : Reimplement Await
-					//case OpCode.Await:
+					case OpCode.Await:
 						return true;
 				}
 			}

ILSpy/Languages/CSharpLanguage.cs

@@ -35,7 +35,9 @@ using ICSharpCode.Decompiler.TypeSystem;
 namespace ICSharpCode.ILSpy
 {
 	/// <summary>
-	/// Decompiler logic for C#.
+	/// C# decompiler integration into ILSpy.
+	/// Note: if you're interested in using the decompiler without the ILSpy UI,
+	/// please directly use the CSharpDecompiler class.
 	/// </summary>
 	[Export(typeof(Language))]
 	public class CSharpLanguage : Language