Merge pull request #2853 from ElektroKill/vb-async

ICSharpCode.Decompiler.Tests/TestCases/VBPretty/.gitignore

@@ -1 +1,3 @@
-*.dll
+/*.dll
+/*.exe
+/*.pdb

ICSharpCode.Decompiler.Tests/TestCases/VBPretty/Async.cs

@@ -1,45 +1,255 @@
 using System;
-using System.IO;
+using System.Collections.Generic;
+using System.Runtime.CompilerServices;
 using System.Threading.Tasks;
 
-namespace EquivalentCSharpConsoleApp
+using Microsoft.VisualBasic.CompilerServices;
+
+namespace ICSharpCode.Decompiler.Tests.TestCases.VBPretty
+{
+	public class Async
+	{
+		private int memberField;
+
+		private static bool True()
+		{
+			return true;
+		}
+
+		public async void SimpleVoidMethod()
+		{
+			Console.WriteLine("Before");
+			await Task.Delay(TimeSpan.FromSeconds(1.0));
+			Console.WriteLine("After");
+		}
+
+		public async void VoidMethodWithoutAwait()
+		{
+			Console.WriteLine("No Await");
+		}
+
+		public async void EmptyVoidMethod()
+		{
+		}
+
+		public async void AwaitYield()
+		{
+			await Task.Yield();
+		}
+
+		public async void AwaitDefaultYieldAwaitable()
+		{
+#if LEGACY_VBC || (OPTIMIZE && !ROSLYN4)
+			YieldAwaitable yieldAwaitable = default(YieldAwaitable);
+			YieldAwaitable yieldAwaitable2 = yieldAwaitable;
+			await yieldAwaitable2;
+#else
+			await default(YieldAwaitable);
+#endif
+		}
+
+		public async void AwaitDefaultHopToThreadPool()
+		{
+#if LEGACY_VBC || (OPTIMIZE && !ROSLYN4)
+			HopToThreadPoolAwaitable hopToThreadPoolAwaitable = default(HopToThreadPoolAwaitable);
+			HopToThreadPoolAwaitable hopToThreadPoolAwaitable2 = hopToThreadPoolAwaitable;
+			await hopToThreadPoolAwaitable2;
+#else
+			await default(HopToThreadPoolAwaitable);
+#endif
+		}
+
+		public async Task SimpleVoidTaskMethod()
+		{
+			Console.WriteLine("Before");
+			await Task.Delay(TimeSpan.FromSeconds(1.0));
+			Console.WriteLine("After");
+		}
+
+		public async Task TaskMethodWithoutAwait()
 		{
-	static class Program
+			Console.WriteLine("No Await");
+		}
+
+		public async Task CapturingThis()
+		{
+			await Task.Delay(memberField);
+		}
+
+		public async Task CapturingThisWithoutAwait()
+		{
+			Console.WriteLine(memberField);
+		}
+
+		public async Task<bool> SimpleBoolTaskMethod()
+		{
+			Console.WriteLine("Before");
+			await Task.Delay(TimeSpan.FromSeconds(1.0));
+			Console.WriteLine("After");
+			return true;
+		}
+
+		public async void TwoAwaitsWithDifferentAwaiterTypes()
 		{
-		public static void Main(string[] args)
+			Console.WriteLine("Before");
+			if (await SimpleBoolTaskMethod())
 			{
-			var task = new Task(ProcessDataAsync);
+				await Task.Delay(TimeSpan.FromSeconds(1.0));
-			task.Start();
+			}
-			task.Wait();
+			Console.WriteLine("After");
-			Console.ReadLine();
 		}
 
-		public async static void ProcessDataAsync()
+		public async void AwaitInLoopCondition()
+		{
+			while (await SimpleBoolTaskMethod())
 			{
-			Task<int> task = HandleFileAsync("C:\\enable1.txt");
+				Console.WriteLine("Body");
-			Console.WriteLine("Please wait, processing");
+			}
-			int result = await task;
-			Console.WriteLine("Count: " + result.ToString());
 		}
 
-		public async static Task<int> HandleFileAsync(string file)
+		public async Task Issue2366a()
 		{
-			Console.WriteLine("HandleFile enter");
+			while (true)
-			int count = 0;
-			using (StreamReader reader = new StreamReader(file))
 			{
-				string value = await reader.ReadToEndAsync();
+				try
-				count += value.Length;
-				for (var i = 0; i <= 10000; i += 1)
 				{
-					var x = value.GetHashCode();
+					await Task.CompletedTask;
-					if (x == 0)
-						count -= 1;
 				}
+				catch (Exception projectError)
+				{
+					ProjectData.SetProjectError(projectError);
+					ProjectData.ClearProjectError();
+				}
+			}
+		}
+
+		public static async Task<int> GetIntegerSumAsync(IEnumerable<int> items)
+		{
+			await Task.Delay(100);
+			int num = 0;
+			foreach (int item in items)
+			{
+				num = checked(num + item);
+			}
+			return num;
 		}
 
-			Console.WriteLine("HandleFile exit");
+		public async Task AsyncCatch(bool b, Task<int> task1, Task<int> task2)
-			return count;
+		{
+			try
+			{
+				Console.WriteLine("Start try");
+				await task1;
+				Console.WriteLine("End try");
+			}
+			catch (Exception projectError)
+			{
+				ProjectData.SetProjectError(projectError);
+				Console.WriteLine("No await");
+				ProjectData.ClearProjectError();
+			}
+		}
+
+		public async Task AsyncCatchThrow(bool b, Task<int> task1, Task<int> task2)
+		{
+			try
+			{
+				Console.WriteLine("Start try");
+				await task1;
+				Console.WriteLine("End try");
+			}
+			catch (Exception projectError)
+			{
+				ProjectData.SetProjectError(projectError);
+				Console.WriteLine("No await");
+				throw;
+			}
+		}
+
+		public async Task AsyncFinally(bool b, Task<int> task1, Task<int> task2)
+		{
+			try
+			{
+				Console.WriteLine("Start try");
+				await task1;
+				Console.WriteLine("End try");
+			}
+			finally
+			{
+				Console.WriteLine("No await");
+			}
+		}
+
+		public static async Task AlwaysThrow()
+		{
+			throw new Exception();
+		}
+
+		public static async Task InfiniteLoop()
+		{
+			while (true)
+			{
+			}
+		}
+
+		public static async Task InfiniteLoopWithAwait()
+		{
+			while (true)
+			{
+				await Task.Delay(10);
+			}
+		}
+
+		public async Task AsyncWithLocalVar()
+		{
+			object objectValue = RuntimeHelpers.GetObjectValue(new object());
+			await UseObj(RuntimeHelpers.GetObjectValue(objectValue));
+			await UseObj(RuntimeHelpers.GetObjectValue(objectValue));
+		}
+
+		public static async Task UseObj(object a)
+		{
+		}
+	}
+
+	public struct AsyncInStruct
+	{
+		private int i;
+
+		public async Task<int> Test(AsyncInStruct xx)
+		{
+			checked
+			{
+				xx.i++;
+				i++;
+				await Task.Yield();
+				return i + xx.i;
+			}
+		}
+	}
+
+	public struct HopToThreadPoolAwaitable : INotifyCompletion
+	{
+		public bool IsCompleted { get; set; }
+
+		public HopToThreadPoolAwaitable GetAwaiter()
+		{
+			return this;
+		}
+
+		public void OnCompleted(Action continuation)
+		{
+			Task.Run(continuation);
+		}
+
+		void INotifyCompletion.OnCompleted(Action continuation)
+		{
+			//ILSpy generated this explicit interface implementation from .override directive in OnCompleted
+			this.OnCompleted(continuation);
+		}
+
+		public void GetResult()
+		{
 		}
 	}
 }

ICSharpCode.Decompiler.Tests/TestCases/VBPretty/Async.vb

@@ -1,47 +1,181 @@
 Imports System
-Imports System.IO
+Imports System.Collections.Generic
-
+Imports System.Threading.Tasks
-Module Program
+Imports System.Runtime.CompilerServices
-    ' Sample taken verbatim from https://www.dotnetperls.com/async-vbnet
+
-    Sub Main(args As String())
+Namespace ICSharpCode.Decompiler.Tests.TestCases.VBPretty
-        Dim task = New Task(AddressOf ProcessDataAsync)
+	Public Class Async
-        ' Start and wait for task to end.
+		Private memberField As Integer
-        task.Start()
+
-        task.Wait()
+		Private Shared Function [True]() As Boolean
-        Console.ReadLine()
+	        Return True
-    End Sub
+	    End Function
-
+
-    Async Sub ProcessDataAsync()
+	    Public Async Sub SimpleVoidMethod()
-        ' Create a task Of Integer.
+	        Console.WriteLine("Before")
-        ' ... Use HandleFileAsync method with a large file.
+	        Await Task.Delay(TimeSpan.FromSeconds(1.0))
-        Dim task As Task(Of Integer) = HandleFileAsync("C:\enable1.txt")
+	        Console.WriteLine("After")
-        ' This statement runs while HandleFileAsync executes.
+	    End Sub
-        Console.WriteLine("Please wait, processing")
+
-        ' Use await to wait for task to complete.
+	    Public Async Sub VoidMethodWithoutAwait()
-        Dim result As Integer = Await task
+	        Console.WriteLine("No Await")
-        Console.WriteLine("Count: " + result.ToString())
+	    End Sub
-    End Sub
+
-
+	    Public Async Sub EmptyVoidMethod()
-    Async Function HandleFileAsync(ByVal file As String) As Task(Of Integer)
+	    End Sub
-        Console.WriteLine("HandleFile enter")
+
-
+	    Public Async Sub AwaitYield()
-        ' Open the file.
+	        Await Task.Yield()
-        Dim count As Integer = 0
+	    End Sub
-        Using reader As StreamReader = New StreamReader(file)
+
-            Dim value As String = Await reader.ReadToEndAsync()
+	    Public Async Sub AwaitDefaultYieldAwaitable()
-            count += value.Length
+	        Await CType(Nothing, YieldAwaitable)
-
+	    End Sub
-            ' Do a slow computation on the file.
+
-            For i = 0 To 10000 Step 1
+		Public Async Sub AwaitDefaultHopToThreadPool()
-                Dim x = value.GetHashCode()
+			' unlike YieldAwaitable which implements ICriticalNotifyCompletion,
-                If x = 0 Then
+			' the HopToThreadPoolAwaitable struct only implements
-                    count -= 1
+			' INotifyCompletion, so this results in different codegen
+			Await CType(Nothing, HopToThreadPoolAwaitable)
+		End Sub
+
+	    Public Async Function SimpleVoidTaskMethod() As Task
+	        Console.WriteLine("Before")
+	        Await Task.Delay(TimeSpan.FromSeconds(1.0))
+	        Console.WriteLine("After")
+	    End Function
+
+	    Public Async Function TaskMethodWithoutAwait() As Task
+	        Console.WriteLine("No Await")
+	    End Function
+
+	    Public Async Function CapturingThis() As Task
+	        Await Task.Delay(memberField)
+	    End Function
+
+	    Public Async Function CapturingThisWithoutAwait() As Task
+	        Console.WriteLine(memberField)
+	    End Function
+
+	    Public Async Function SimpleBoolTaskMethod() As Task(Of Boolean)
+	        Console.WriteLine("Before")
+	        Await Task.Delay(TimeSpan.FromSeconds(1.0))
+	        Console.WriteLine("After")
+	        Return True
+	    End Function
+
+	    Public Async Sub TwoAwaitsWithDifferentAwaiterTypes()
+	        Console.WriteLine("Before")
+	        If Await SimpleBoolTaskMethod() Then
+	            Await Task.Delay(TimeSpan.FromSeconds(1.0))
 	        End If
+	        Console.WriteLine("After")
+	    End Sub
+
+	    Public Async Sub AwaitInLoopCondition()
+	        While Await SimpleBoolTaskMethod()
+	            Console.WriteLine("Body")
+	        End While
+	    End Sub
+
+		Public Async Function Issue2366a() As Task
+			While True
+				Try
+					Await Task.CompletedTask
+				Catch
+				End Try
+			End While
+		End Function
 
+	    Public Shared Async Function GetIntegerSumAsync(ByVal items As IEnumerable(Of Integer)) As Task(Of Integer)
+	        Await Task.Delay(100)
+	        Dim num = 0
+	        For Each item In items
+	            num += item
 	        Next
-        End Using
+	        Return num
+	    End Function
+
+		 Public Async Function AsyncCatch(ByVal b As Boolean, ByVal task1 As Task(Of Integer), ByVal task2 As Task(Of Integer)) As Task
+			 Try
+				 Console.WriteLine("Start try")
+				 Await task1
+				 Console.WriteLine("End try")
+			 Catch ex As Exception
+				 Console.WriteLine("No await")
+			 End Try
+		 End Function
+
+		 Public Async Function AsyncCatchThrow(ByVal b As Boolean, ByVal task1 As Task(Of Integer), ByVal task2 As Task(Of Integer)) As Task
+			 Try
+				 Console.WriteLine("Start try")
+				 Await task1
+				 Console.WriteLine("End try")
+			 Catch ex As Exception
+				 Console.WriteLine("No await")
+				 Throw
+			 End Try
+		 End Function
+
+		 Public Async Function AsyncFinally(ByVal b As Boolean, ByVal task1 As Task(Of Integer), ByVal task2 As Task(Of Integer)) As Task
+			 Try
+				 Console.WriteLine("Start try")
+				 Await task1
+				 Console.WriteLine("End try")
+			 Finally
+				 Console.WriteLine("No await")
+			 End Try
+		 End Function
+
+	    Public Shared Async Function AlwaysThrow() As Task
+	    Throw New Exception
+	    End Function
+
+	    Public Shared Async Function InfiniteLoop() As Task
+	        While True
+	        End While
+	    End Function
 
-        Console.WriteLine("HandleFile exit")
+	    Public Shared Async Function InfiniteLoopWithAwait() As Task
-        Return count
+	        While True
+	            Await Task.Delay(10)
+	        End While
 	    End Function
-End Module
+
+		Public Async Function AsyncWithLocalVar() As Task
+	        Dim a As Object = New Object()
+	        Await UseObj(a)
+	        Await UseObj(a)
+	    End Function
+
+	    Public Shared Async Function UseObj(ByVal a As Object) As Task
+	    End Function
+	End Class
+
+	Public Structure AsyncInStruct
+		Private i As Integer
+
+		Public Async Function Test(ByVal xx As AsyncInStruct) As Task(Of Integer)
+			xx.i += 1
+			i += 1
+			Await Task.Yield()
+			Return i + xx.i
+		End Function
+	End Structure
+
+	Public Structure HopToThreadPoolAwaitable
+		Implements INotifyCompletion
+		Public Property IsCompleted As Boolean
+
+		Public Function GetAwaiter() As HopToThreadPoolAwaitable
+			Return Me
+		End Function
+
+		Public Sub OnCompleted(ByVal continuation As Action) Implements INotifyCompletion.OnCompleted
+			Task.Run(continuation)
+		End Sub
+
+		Public Sub GetResult()
+		End Sub
+	End Structure
+End Namespace

ICSharpCode.Decompiler.Tests/VBPrettyTestRunner.cs

@@ -89,10 +89,10 @@ namespace ICSharpCode.Decompiler.Tests
 			CompilerOptions.Optimize | CompilerOptions.UseRoslynLatest,
 		};
 
-		[Test, Ignore("Implement VB async/await")]
+		[Test]
 		public async Task Async([ValueSource(nameof(defaultOptions))] CompilerOptions options)
 		{
-			await Run(options: options);
+			await Run(options: options | CompilerOptions.Library);
 		}
 
 		[Test] // TODO: legacy VB compound assign
@@ -142,7 +142,7 @@ namespace ICSharpCode.Decompiler.Tests
 			}
 
 			var executable = await Tester.CompileVB(vbFile, options | CompilerOptions.ReferenceVisualBasic, exeFile).ConfigureAwait(false);
-			var decompiled = await Tester.DecompileCSharp(executable.PathToAssembly, settings).ConfigureAwait(false);
+			var decompiled = await Tester.DecompileCSharp(executable.PathToAssembly, settings ?? new DecompilerSettings { FileScopedNamespaces = false }).ConfigureAwait(false);
 
 			CodeAssert.FilesAreEqual(csFile, decompiled, Tester.GetPreprocessorSymbols(options).ToArray());
 			Tester.RepeatOnIOError(() => File.Delete(decompiled));

ICSharpCode.Decompiler/IL/ControlFlow/AsyncAwaitDecompiler.cs

@@ -1,4 +1,4 @@
-// Copyright (c) 2017 Daniel Grunwald
+// Copyright (c) 2017 Daniel Grunwald
 // 
 // Permission is hereby granted, free of charge, to any person obtaining a copy of this
 // software and associated documentation files (the "Software"), to deal in the Software
@@ -105,6 +105,8 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 		// across the yield point.
 		Dictionary<Block, (ILVariable awaiterVar, IField awaiterField)> awaitBlocks = new Dictionary<Block, (ILVariable awaiterVar, IField awaiterField)>();
 
+		bool isVisualBasicStateMachine;
+
 		int catchHandlerOffset;
 		List<AsyncDebugInfo.Await> awaitDebugInfos = new List<AsyncDebugInfo.Await>();
 
@@ -158,8 +160,11 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			// and inlining because TranslateFieldsToLocalAccess() might have opened up new inlining opportunities.
 			function.RunTransforms(CSharpDecompiler.EarlyILTransforms(), context);
 
+			if (!isVisualBasicStateMachine)
+			{
 				AwaitInCatchTransform.Run(function, context);
 				AwaitInFinallyTransform.Run(function, context);
+			}
 
 			awaitDebugInfos.SortBy(row => row.YieldOffset);
 			function.AsyncDebugInfo = new AsyncDebugInfo(catchHandlerOffset, awaitDebugInfos.ToImmutableArray());
@@ -180,6 +185,23 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 				EarlyExpressionTransforms.StObjToStLoc(stobj, context);
 			}
 
+			if (isVisualBasicStateMachine)
+			{
+				// Visual Basic state machines often contain stack slots for ldflda instruction for the builder field.
+				// This messes up the matching code in AnalyzeAwaitBlock() and causes it to fail.
+				// Propagating these stack stores makes the matching code work without the need for a lot of
+				// additional matching code to handle these stack slots.
+				foreach (var stloc in function.Descendants.OfType<StLoc>().Where(s => s.Variable.Kind == VariableKind.StackSlot && s.Variable.IsSingleDefinition
+							&& s.Value.MatchLdFlda(out var target, out var field) && field.Equals(builderField) && target.MatchLdThis()).ToList())
+				{
+					CopyPropagation.Propagate(stloc, context);
+				}
+
+				// Remove lone 'ldc.i4', present in older Roslyn VB compiler output
+				foreach (var block in function.Descendants.OfType<Block>())
+					block.Instructions.RemoveAll(inst => inst.OpCode == OpCode.LdcI4);
+			}
+
 			// Copy-propagate temporaries holding a copy of 'this'.
 			foreach (var stloc in function.Descendants.OfType<StLoc>().Where(s => s.Variable.IsSingleDefinition && s.Value.MatchLdThis()).ToList())
 			{
@@ -335,6 +357,19 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 					return false;
 			}
 
+			if (IsPotentialVisualBasicStateMachineInitialiation(body[0], stateMachineVar))
+			{
+				// Visual Basic compiler uses a different order of field assignements
+				if (MatchVisualBasicStateMachineFieldAssignements(body, stateMachineVar))
+				{
+					isVisualBasicStateMachine = true;
+					return true;
+				}
+				// If the Visual Basic matching code failed, reset the map in case it
+				// was partially populated and try matching the C# state machine initialization.
+				fieldToParameterMap.Clear();
+			}
+
 			// Check the last field assignment - this should be the state field
 			// stfld <>1__state(ldloca stateField, ldc.i4 -1)
 			if (!MatchStFld(body[pos], stateMachineVar, out stateField, out var initialStateExpr))
@@ -388,6 +423,62 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			return builderFieldIsInitialized;
 		}
 
+		bool IsPotentialVisualBasicStateMachineInitialiation(ILInstruction inst, ILVariable stateMachineVar)
+		{
+			// stobj VB$StateMachine(ldloca stateMachine, default.value VB$StateMachine)
+			// Used by VBC (Debug and Release) and Roslyn VB (Release) builds
+			if (inst.MatchStObj(out var target, out var val, out var type1) && target.MatchLdLoca(stateMachineVar) &&
+				val.MatchDefaultValue(out var type2) && type1.Equals(type2))
+				return true;
+			// stloc stateMachine(newobj VB$StateMachine..ctor())
+			// Used by Roslyn VB (Debug) builds
+			if (inst.MatchStLoc(stateMachineVar, out var init) && init is NewObj newObj && newObj.Arguments.Count == 0 &&
+				stateMachineType.Equals(newObj.Method.DeclaringTypeDefinition))
+				return true;
+			return false;
+		}
+
+		bool MatchVisualBasicStateMachineFieldAssignements(IList<ILInstruction> body, ILVariable stateMachineVar)
+		{
+			// stfld $State(ldloca stateField, ldc.i4 -1)
+			if (!MatchStFld(body[body.Count - 4], stateMachineVar, out stateField, out var initialStateExpr))
+				return false;
+			if (!initialStateExpr.MatchLdcI4(out initialState))
+				return false;
+			if (initialState != -1)
+				return false;
+
+			// stfld $Builder(ldloca stateMachine, call Create())
+			if (!MatchStFld(body[body.Count - 3], stateMachineVar, out var builderField2, out var fieldInit))
+				return false;
+			if (!builderField.Equals(builderField2))
+				return false;
+			if (fieldInit is not Call { Method: { Name: "Create" }, Arguments: { Count: 0 } })
+				return false;
+
+			for (int i = 1; i < body.Count - 4; i++)
+			{
+				if (!MatchStFld(body[i], stateMachineVar, out var field, out fieldInit))
+					return false;
+				// Legacy Visual Basic compiler can emit a call to RuntimeHelpers.GetObjectValue here
+				if (fieldInit is Call call && call.Arguments.Count == 1 && call.Method.IsStatic && call.Method.Name == "GetObjectValue")
+					fieldInit = call.Arguments[0];
+				if (fieldInit.MatchLdLoc(out var v) && v.Kind == VariableKind.Parameter)
+				{
+					// OK, copies parameter into state machine
+					fieldToParameterMap[field] = v;
+				}
+				else if (fieldInit is LdObj ldobj && ldobj.Target.MatchLdThis())
+				{
+					// stfld <>4__this(ldloc stateMachine, ldobj AsyncInStruct(ldloc this))
+					fieldToParameterMap[field] = ((LdLoc)ldobj.Target).Variable;
+				}
+				else
+					return false;
+			}
+			return true;
+		}
+
 		/// <summary>
 		/// Matches a (potentially virtual) instance method call.
 		/// </summary>
@@ -622,6 +713,14 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			bool[] blocksAnalyzed = new bool[blockContainer.Blocks.Count];
 			cachedStateVar = null;
 			int pos = 0;
+			// Visual Basic state machines initialize doFinallyBodies at the start of MoveNext()
+			// stloc doFinallyBodies(ldc.i4 1)
+			if (isVisualBasicStateMachine && blockContainer.EntryPoint.Instructions[pos].MatchStLoc(out var v, out var ldci4) &&
+				ldci4.MatchLdcI4(1))
+			{
+				doFinallyBodies = v;
+				pos++;
+			}
 			while (blockContainer.EntryPoint.Instructions[pos] is StLoc stloc)
 			{
 				// stloc V_1(ldfld <>4__this(ldloc this))
@@ -651,6 +750,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 				throw new SymbolicAnalysisFailedException();
 			// CatchHandler will be validated in ValidateCatchBlock()
 
+			// stloc doFinallyBodies(ldc.i4 1)
 			if (((BlockContainer)mainTryCatch.TryBlock).EntryPoint.Instructions[0] is StLoc initDoFinallyBodies
 				&& initDoFinallyBodies.Variable.Kind == VariableKind.Local
 				&& initDoFinallyBodies.Variable.Type.IsKnownType(KnownTypeCode.Boolean)
@@ -715,10 +815,36 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			}
 
 			var block = blockContainer.Blocks[setResultReturnBlockIndex];
-			// stfld <>1__state(ldloc this, ldc.i4 -2)
+
 			int pos = 0;
+			// [vb-only] stloc S_10(ldloc this)
+			if (block.Instructions[pos] is StLoc stlocThisCache && stlocThisCache.Value.MatchLdThis() &&
+				stlocThisCache.Variable.Kind == VariableKind.StackSlot)
+			{
+				pos++;
+			}
+			// [vb-only] stloc S_11(ldc.i4 -2)
+			ILVariable finalStateSlot = null;
+			int? finalStateSlotValue = null;
+			if (block.Instructions[pos] is StLoc stlocFinalState && stlocFinalState.Value is LdcI4 ldcI4 &&
+				stlocFinalState.Variable.Kind == VariableKind.StackSlot)
+			{
+				finalStateSlot = stlocFinalState.Variable;
+				finalStateSlotValue = ldcI4.Value;
+				pos++;
+			}
+			// [vb-only] stloc cachedStateVar(ldloc S_11)
+			if (block.Instructions[pos] is StLoc stlocCachedState && stlocCachedState.Variable.Kind == VariableKind.Local &&
+				stlocCachedState.Variable.Index == cachedStateVar?.Index && stlocCachedState.Value.MatchLdLoc(finalStateSlot))
+			{
+				pos++;
+			}
+
+			// stfld <>1__state(ldloc this, ldc.i4 -2)
 			if (!MatchStateAssignment(block.Instructions[pos], out finalState))
 				throw new SymbolicAnalysisFailedException();
+			if (finalStateSlotValue is not null && finalState != finalStateSlotValue.Value)
+				throw new SymbolicAnalysisFailedException();
 			finalStateKnown = true;
 			pos++;
 
@@ -874,13 +1000,20 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			bool[] blocksAnalyzed = new bool[handlerContainer.Blocks.Count];
 			var catchBlock = handlerContainer.EntryPoint;
 			catchHandlerOffset = catchBlock.StartILOffset;
+			int pos = 0;
+			// [vb-only] call SetProjectError(ldloc E_143)
+			if (isVisualBasicStateMachine && catchBlock.Instructions[pos] is Call call && call.Method.Name == "SetProjectError" &&
+				call.Arguments.Count == 1 && call.Arguments[0].MatchLdLoc(handler.Variable))
+			{
+				pos++;
+			}
 			// stloc exception(ldloc E_143)
-			if (!(catchBlock.Instructions[0] is StLoc stloc))
+			if (!(catchBlock.Instructions[pos++] is StLoc stloc))
 				throw new SymbolicAnalysisFailedException();
 			if (!stloc.Value.MatchLdLoc(handler.Variable))
 				throw new SymbolicAnalysisFailedException();
 			// stfld <>1__state(ldloc this, ldc.i4 -2)
-			if (!MatchStateAssignment(catchBlock.Instructions[1], out int newState))
+			if (!MatchStateAssignment(catchBlock.Instructions[pos++], out int newState))
 				throw new SymbolicAnalysisFailedException();
 			if (finalStateKnown)
 			{
@@ -892,7 +1025,6 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 				finalState = newState;
 				finalStateKnown = true;
 			}
-			int pos = 2;
 			if (pos + 2 == catchBlock.Instructions.Count && catchBlock.MatchIfAtEndOfBlock(out var condition, out var trueInst, out var falseInst))
 			{
 				if (MatchDisposeCombinedTokens(handlerContainer, condition, trueInst, falseInst, blocksAnalyzed, out var setResultAndExitBlock))
@@ -924,6 +1056,13 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			// [optional] call Complete(ldfld <>t__builder(ldloc this))
 			MatchCompleteCall(catchBlock, ref pos);
 
+			// [vb-only] call ClearProjectError()
+			if (isVisualBasicStateMachine && catchBlock.Instructions[pos] is Call call2 &&
+				call2.Method.Name == "ClearProjectError" && call2.Arguments.Count == 0)
+			{
+				pos++;
+			}
+
 			// leave IL_0000
 			if (!catchBlock.Instructions[pos].MatchLeave((BlockContainer)moveNextFunction.Body))
 				throw new SymbolicAnalysisFailedException();
@@ -1594,8 +1733,47 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			if (!RestoreStack(block, ref pos, stackField))
 				return false;
 
+			// Visual Basic state machines use a different order of field assignements.
+			if (isVisualBasicStateMachine)
+			{
+				// stloc S_28(ldc.i4 -1)
+				// stloc cachedStateVar(ldloc S_28)
+				// stfld <>1__state(ldloc this, ldloc S_28)
+				if (!MatchStateFieldAssignement(block, ref pos))
+					return false;
+				pos++;
+
+				// stloc awaiterVar(ldfld awaiterField(ldloc this))
+				if (!MatchStoreToAwaiterVariable(block.Instructions[pos]))
+					return false;
+				pos++;
+
+				// [optional] stfld awaiterField(ldloc this, default.value)
+				MatchResetAwaiterField(block, ref pos);
+			}
+			else
+			{
 				// stloc awaiterVar(ldfld awaiterField(ldloc this))
-			if (!block.Instructions[pos].MatchStLoc(awaiterVar, out var value))
+				if (!MatchStoreToAwaiterVariable(block.Instructions[pos]))
+					return false;
+				pos++;
+
+				// [optional] stfld awaiterField(ldloc this, default.value)
+				MatchResetAwaiterField(block, ref pos);
+
+				// stloc S_28(ldc.i4 -1)
+				// stloc cachedStateVar(ldloc S_28)
+				// stfld <>1__state(ldloc this, ldloc S_28)
+				if (!MatchStateFieldAssignement(block, ref pos))
+					return false;
+				pos++;
+			}
+			return block.Instructions[pos].MatchBranch(completedBlock);
+
+			bool MatchStoreToAwaiterVariable(ILInstruction instr)
+			{
+				// stloc awaiterVar(ldfld awaiterField(ldloc this))
+				if (!instr.MatchStLoc(awaiterVar, out var value))
 					return false;
 				if (value is CastClass cast && cast.Type.Equals(awaiterVar.Type))
 				{
@@ -1609,10 +1787,13 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 					return false;
 				if (!field.Equals(awaiterField))
 					return false;
-			pos++;
+				return true;
+			}
 
+			void MatchResetAwaiterField(Block block, ref int pos)
+			{
 				// stfld awaiterField(ldloc this, default.value)
-			if (block.Instructions[pos].MatchStFld(out target, out field, out value)
+				if (block.Instructions[pos].MatchStFld(out var target, out var field, out var value)
 					&& target.MatchLdThis()
 					&& field.Equals(awaiterField)
 					&& (value.OpCode == OpCode.DefaultValue || value.OpCode == OpCode.LdNull))
@@ -1631,7 +1812,10 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 						pos += 2;
 					}
 				}
+			}
 
+			bool MatchStateFieldAssignement(Block block, ref int pos)
+			{
 				// stloc S_28(ldc.i4 -1)
 				// stloc cachedStateVar(ldloc S_28)
 				// stfld <>1__state(ldloc this, ldloc S_28)
@@ -1649,22 +1833,16 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 							pos++;
 					}
 				}
-			if (block.Instructions[pos].MatchStFld(out target, out field, out value))
+				if (!block.Instructions[pos].MatchStFld(out var target, out var field, out var value))
-			{
+					return false;
 				if (!target.MatchLdThis())
 					return false;
 				if (!field.MemberDefinition.Equals(stateField.MemberDefinition))
 					return false;
 				if (!(value.MatchLdcI4(initialState) || value.MatchLdLoc(m1Var)))
 					return false;
-				pos++;
+				return true;
-			}
-			else
-			{
-				return false;
 			}
-
-			return block.Instructions[pos].MatchBranch(completedBlock);
 		}
 
 		private bool RestoreStack(Block block, ref int pos, IField stackField)