added notnullwhen annotations

.editorconfig

@@ -152,6 +152,7 @@ dotnet_diagnostic.MEF006.severity = silent
 dotnet_diagnostic.IDE2003.severity = silent
 
 #cleared null error types
+dotnet_diagnostic.CS8612.severity = error
 dotnet_diagnostic.CS8714.severity = error
 dotnet_diagnostic.CS8765.severity = error
 dotnet_diagnostic.CS8766.severity = error

ICSharpCode.BamlDecompiler/Rewrite/ConnectionIdRewritePass.cs

@@ -22,15 +22,16 @@ using System.Linq;
 using System.Reflection.Metadata;
 using System.Xml.Linq;
 
+using ICSharpCode.BamlDecompiler.Xaml;
 using ICSharpCode.Decompiler.CSharp;
 using ICSharpCode.Decompiler.IL;
 using ICSharpCode.Decompiler.IL.Transforms;
 using ICSharpCode.Decompiler.Util;
 
-using ICSharpCode.BamlDecompiler.Xaml;
-
 namespace ICSharpCode.BamlDecompiler.Rewrite
 {
+	using System.Diagnostics.CodeAnalysis;
+
 	using ICSharpCode.Decompiler.TypeSystem;
 
 	internal class ConnectionIdRewritePass : IRewritePass
@@ -249,7 +250,7 @@ namespace ICSharpCode.BamlDecompiler.Rewrite
 			}
 		}
 
-		bool MatchFieldAssignment(ILInstruction inst, out FieldAssignment field)
+		bool MatchFieldAssignment(ILInstruction inst, [NotNullWhen(true)] out FieldAssignment field)
 		{
 			field = null;
 			if (!inst.MatchStFld(out _, out var fld, out var value) || !value.MatchCastClass(out var arg, out _)
@@ -293,7 +294,7 @@ namespace ICSharpCode.BamlDecompiler.Rewrite
 		// callvirt set_Event(ldloc v, ldsfld eventName)
 		// callvirt set_Handler(ldloc v, newobj RoutedEventHandler..ctor(ldloc this, ldftn eventHandler))
 		// callvirt Add(callvirt get_Setters(castclass System.Windows.Style(ldloc target)), ldloc v)
-		bool MatchEventSetterCreation(Block b, ref int pos, out EventRegistration @event)
+		bool MatchEventSetterCreation(Block b, ref int pos, [NotNullWhen(true)] out EventRegistration? @event)
 		{
 			@event = null;
 			if (!b.FinalInstruction.MatchNop())
@@ -362,7 +363,7 @@ namespace ICSharpCode.BamlDecompiler.Rewrite
 			return true;
 		}
 
-		bool MatchSimpleEventRegistration(ILInstruction inst, out EventRegistration @event)
+		bool MatchSimpleEventRegistration(ILInstruction inst, [NotNullWhen(true)] out EventRegistration? @event)
 		{
 			@event = null;
 			if (!(inst is CallInstruction call) || call.OpCode == OpCode.NewObj)

ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs

@@ -19,6 +19,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.IO;
 using System.Linq;
 using System.Reflection.Metadata;
@@ -406,7 +407,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		static readonly Regex automaticPropertyBackingFieldRegex = new Regex(@"^<(.*)>k__BackingField$",
 			RegexOptions.Compiled | RegexOptions.CultureInvariant);
 
-		static bool IsAutomaticPropertyBackingField(FieldDefinition field, MetadataReader metadata, out string? propertyName)
+		static bool IsAutomaticPropertyBackingField(FieldDefinition field, MetadataReader metadata, [NotNullWhen(true)] out string? propertyName)
 		{
 			propertyName = null;
 			var name = metadata.GetString(field.Name);
@@ -1917,7 +1918,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			return found;
 		}
 
-		bool FindAttribute(EntityDeclaration entityDecl, KnownAttribute attributeType, out Syntax.Attribute? attribute)
+		bool FindAttribute(EntityDeclaration entityDecl, KnownAttribute attributeType, [NotNullWhen(true)] out Syntax.Attribute? attribute)
 		{
 			attribute = null;
 			foreach (var section in entityDecl.Attributes)

ICSharpCode.Decompiler/CSharp/CallBuilder.cs

@@ -698,7 +698,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			);
 		}
 
-		private bool TryGetStringInterpolationTokens(ArgumentList argumentList, out string? format, out List<(TokenKind Kind, int Index, int Alignment, string? Format)>? tokens)
+		private bool TryGetStringInterpolationTokens(ArgumentList argumentList, [NotNullWhen(true)] out string? format, [NotNullWhen(true)] out List<(TokenKind Kind, int Index, int Alignment, string? Format)>? tokens)
 		{
 			tokens = null;
 			format = null;
@@ -1823,7 +1823,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			return expr.Expression.WithRR(new MemberResolveResult(null, method));
 		}
 
-		ExpressionWithResolveResult BuildDelegateReference(IMethod method, IMethod invokeMethod, ExpectedTargetDetails expectedTargetDetails, ILInstruction thisArg)
+		ExpressionWithResolveResult BuildDelegateReference(IMethod method, IMethod? invokeMethod, ExpectedTargetDetails expectedTargetDetails, ILInstruction thisArg)
 		{
 			ExpressionBuilder expressionBuilder = this.expressionBuilder;
 			ExpressionWithResolveResult targetExpression;
@@ -1983,7 +1983,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			return oce;
 		}
 
-		bool IsUnambiguousMethodReference(ExpectedTargetDetails expectedTargetDetails, IMethod method, ResolveResult target, IReadOnlyList<IType> typeArguments, bool isExtensionMethodReference, out ResolveResult result)
+		bool IsUnambiguousMethodReference(ExpectedTargetDetails expectedTargetDetails, IMethod method, ResolveResult target, IReadOnlyList<IType> typeArguments, bool isExtensionMethodReference, [NotNullWhen(true)] out ResolveResult result)
 		{
 			Log.WriteLine("IsUnambiguousMethodReference: Performing overload resolution for " + method);
 

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -3545,7 +3545,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		{
 			var stloc = block.Instructions.FirstOrDefault() as StLoc;
 			var final = block.FinalInstruction as LdLoc;
-			if (stloc == null || final == null || !stloc.Value.MatchNewArr(out IType type))
+			if (stloc == null || final == null || !stloc.Value.MatchNewArr(out IType? type))
 				throw new ArgumentException("given Block is invalid!");
 			if (stloc.Variable != final.Variable || stloc.Variable.Kind != VariableKind.InitializerTarget)
 				throw new ArgumentException("given Block is invalid!");
@@ -3564,11 +3564,11 @@ namespace ICSharpCode.Decompiler.CSharp
 
 			for (int i = 1; i < block.Instructions.Count; i++)
 			{
-				if (!block.Instructions[i].MatchStObj(out ILInstruction target, out ILInstruction value, out IType t) || !type.Equals(t))
+				if (!block.Instructions[i].MatchStObj(out ILInstruction? target, out ILInstruction? value, out IType? t) || !type.Equals(t))
 					throw new ArgumentException("given Block is invalid!");
-				if (!target.MatchLdElema(out t, out ILInstruction array) || !type.Equals(t))
+				if (!target.MatchLdElema(out t, out ILInstruction? array) || !type.Equals(t))
 					throw new ArgumentException("given Block is invalid!");
-				if (!array.MatchLdLoc(out ILVariable v) || v != final.Variable)
+				if (!array.MatchLdLoc(out ILVariable? v) || v != final.Variable)
 					throw new ArgumentException("given Block is invalid!");
 				while (container.Count < dimensions)
 				{

ICSharpCode.Decompiler/CSharp/RecordDecompiler.cs

@@ -19,6 +19,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Reflection.Metadata;
 using System.Threading;
@@ -39,8 +40,8 @@ namespace ICSharpCode.Decompiler.CSharp
 		readonly bool isInheritedRecord;
 		readonly bool isStruct;
 		readonly bool isSealed;
-		readonly IMethod primaryCtor;
-		readonly IType baseClass;
+		readonly IMethod? primaryCtor;
+		readonly IType? baseClass;
 		readonly Dictionary<IField, IProperty> backingFieldToAutoProperty = new Dictionary<IField, IProperty>();
 		readonly Dictionary<IProperty, IField> autoPropertyToBackingField = new Dictionary<IProperty, IField>();
 		readonly Dictionary<IParameter, IMember> primaryCtorParameterToAutoPropertyOrBackingField = new Dictionary<IParameter, IMember>();
@@ -75,7 +76,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				}
 			}
 
-			bool IsAutoProperty(IProperty p, out IField? field)
+			bool IsAutoProperty(IProperty p, [NotNullWhen(true)] out IField? field)
 			{
 				field = null;
 				if (p.IsStatic)
@@ -108,7 +109,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				return field.Name == $"<{p.Name}>k__BackingField";
 			}
 
-			bool IsAutoGetter(IMethod method, out IField? field)
+			bool IsAutoGetter(IMethod method, [NotNullWhen(true)] out IField? field)
 			{
 				field = null;
 				var body = DecompileBody(method);
@@ -129,7 +130,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				}
 			}
 
-			bool IsAutoSetter(IMethod method, out IField? field)
+			bool IsAutoSetter(IMethod method, [NotNullWhen(true)] out IField? field)
 			{
 				field = null;
 				Debug.Assert(!method.IsStatic);
@@ -137,7 +138,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				if (body == null)
 					return false;
 				// this.field = value;
-				ILInstruction valueInst;
+				ILInstruction? valueInst;
 				if (method.IsStatic)
 				{
 					if (!body.Instructions[0].MatchStsFld(out field, out valueInst))
@@ -158,7 +159,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			}
 		}
 
-		IMethod DetectPrimaryConstructor()
+		IMethod? DetectPrimaryConstructor()
 		{
 			if (recordTypeDef.IsRecord)
 			{
@@ -373,7 +374,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				&& autoPropertyOrBackingFieldToPrimaryCtorParameter.ContainsKey((IProperty)property.Specialize(subst));
 		}
 
-		internal (IProperty prop, IField field) GetPropertyInfoByPrimaryConstructorParameter(IParameter parameter)
+		internal (IProperty? prop, IField field) GetPropertyInfoByPrimaryConstructorParameter(IParameter parameter)
 		{
 			var member = primaryCtorParameterToAutoPropertyOrBackingField[parameter];
 			if (member is IField field)
@@ -450,8 +451,14 @@ namespace ICSharpCode.Decompiler.CSharp
 			{
 				if (!(member is IField field))
 				{
-					if (!autoPropertyToBackingField.TryGetValue((IProperty)member, out field))
+					if (!autoPropertyToBackingField.TryGetValue((IProperty)member, out var fieldHolder))
+					{
 						continue;
+					}
+					else
+					{
+						field = fieldHolder;
+					}
 				}
 				if (pos >= body.Instructions.Count)
 					return false;
@@ -516,7 +523,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			if (!(body.Instructions.Single() is Leave leave))
 				return false;
 			// leave IL_0000 (call GetTypeFromHandle(ldtypetoken R))
-			if (!TransformExpressionTrees.MatchGetTypeFromHandle(leave.Value, out IType ty))
+			if (!TransformExpressionTrees.MatchGetTypeFromHandle(leave.Value, out IType? ty))
 				return false;
 			return IsRecordType(ty);
 		}
@@ -569,7 +576,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				trueInst = Block.Unwrap(trueInst);
 				if (!MatchStringBuilderAppend(trueInst, builder, out var val))
 					return false;
-				if (!(val.MatchLdStr(out string text) && text == ", "))
+				if (!(val.MatchLdStr(out string? text) && text == ", "))
 					return false;
 				pos++;
 
@@ -601,7 +608,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				callvirt Append(ldloc builder, ldstr " = ")
 				callvirt Append(ldloc builder, constrained[System.Int32].callvirt ToString(ldflda B(ldloc this)))
 				leave IL_0000 (ldc.i4 1) */
-				if (!MatchStringBuilderAppendConstant(out string text))
+				if (!MatchStringBuilderAppendConstant(out string? text))
 					return false;
 				string expectedText = (needsComma ? ", " : "") + member.Name + " = ";
 				if (text != expectedText)
@@ -672,10 +679,10 @@ namespace ICSharpCode.Decompiler.CSharp
 				return true;
 			}
 
-			bool MatchStringBuilderAppendConstant(out string? text)
+			bool MatchStringBuilderAppendConstant([NotNullWhen(true)] out string? text)
 			{
 				text = null;
-				while (MatchStringBuilderAppend(body.Instructions[pos], builder, out var val) && val.MatchLdStr(out string valText))
+				while (MatchStringBuilderAppend(body.Instructions[pos], builder, out var val) && val.MatchLdStr(out string? valText))
 				{
 					text += valText;
 					pos++;
@@ -684,7 +691,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			}
 		}
 
-		private bool MatchStringBuilderAppend(ILInstruction inst, ILVariable sb, out ILInstruction? val)
+		private bool MatchStringBuilderAppend(ILInstruction inst, ILVariable sb, [NotNullWhen(true)] out ILInstruction? val)
 		{
 			val = null;
 			if (!(inst is CallVirt { Method: { Name: "Append", DeclaringType: { Namespace: "System.Text", Name: "StringBuilder" } } } call))
@@ -760,7 +767,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				{
 					return val != null && val.Length == 1 && call.Arguments[1].MatchLdcI4(val[0]);
 				}
-				return call.Arguments[1].MatchLdStr(out string val1) && val1 == val;
+				return call.Arguments[1].MatchLdStr(out string? val1) && val1 == val;
 			}
 		}
 
@@ -912,7 +919,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			}
 		}
 
-		private bool MatchGetEqualityContract(ILInstruction inst, out ILInstruction? target)
+		private bool MatchGetEqualityContract(ILInstruction inst, [NotNullWhen(true)] out ILInstruction? target)
 		{
 			target = null;
 			if (!(inst is CallInstruction { Method: { Name: "get_EqualityContract" } } call))
@@ -1099,7 +1106,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			return returnInst != null && returnInst.MatchReturn(out var retVal) && retVal.MatchNop();
 		}
 
-		bool MatchMemberAccess(ILInstruction inst, out ILInstruction? target, out IMember? member)
+		bool MatchMemberAccess(ILInstruction inst, [NotNullWhen(true)] out ILInstruction? target, [NotNullWhen(true)] out IMember? member)
 		{
 			target = null;
 			member = null;
@@ -1116,12 +1123,17 @@ namespace ICSharpCode.Decompiler.CSharp
 				member = property;
 				return true;
 			}
-			else if (inst.MatchLdFld(out target, out IField field))
+			else if (inst.MatchLdFld(out target, out IField? field))
 			{
-				if (backingFieldToAutoProperty.TryGetValue(field, out property))
+				if (backingFieldToAutoProperty.TryGetValue(field, out var propertyHolder))
+				{
+					property = propertyHolder;
 					member = property;
+				}
 				else
+				{
 					member = field;
+				}
 				return true;
 			}
 			else
@@ -1130,7 +1142,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			}
 		}
 
-		Block DecompileBody(IMethod method)
+		Block? DecompileBody(IMethod method)
 		{
 			if (method == null || method.MetadataToken.IsNil)
 				return null;

ICSharpCode.Decompiler/CSharp/Resolver/CSharpResolver.cs

@@ -20,6 +20,7 @@ using System;
 using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 
 using ICSharpCode.Decompiler.CSharp.Syntax;
@@ -1597,7 +1598,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			}
 		}
 
-		public bool IsVariableReferenceWithSameType(ResolveResult rr, string identifier, out TypeResolveResult? trr)
+		public bool IsVariableReferenceWithSameType(ResolveResult rr, string identifier, [NotNullWhen(true)] out TypeResolveResult? trr)
 		{
 			if (!(rr is MemberResolveResult || rr is LocalResolveResult))
 			{

ICSharpCode.Decompiler/CSharp/StatementBuilder.cs

@@ -19,6 +19,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Threading;
 
@@ -875,7 +876,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			return NormalizeTypeVisitor.TypeErasure.EquivalentTypes(a, b);
 		}
 
-		private bool IsDynamicCastToIEnumerable(Expression expr, out Expression? dynamicExpr)
+		private bool IsDynamicCastToIEnumerable(Expression expr, [NotNullWhen(true)] out Expression? dynamicExpr)
 		{
 			if (!(expr is CastExpression cast))
 			{

ICSharpCode.Decompiler/CSharp/Syntax/TypeSystemAstBuilder.cs

@@ -20,6 +20,7 @@ using System;
 using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Reflection;
 using System.Runtime.CompilerServices;
@@ -1081,7 +1082,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 			}
 		}
 
-		bool IsSpecialConstant(IType expectedType, object constant, out Expression? expression)
+		bool IsSpecialConstant(IType expectedType, object constant, [NotNullWhen(true)] out Expression? expression)
 		{
 			expression = null;
 			if (!specialConstants.TryGetValue(constant, out var info))
@@ -2492,7 +2493,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 			return new NamespaceDeclaration(ns.FullName);
 		}
 
-		AstType GetExplicitInterfaceType(IMember member)
+		AstType? GetExplicitInterfaceType(IMember member)
 		{
 			if (member.IsExplicitInterfaceImplementation)
 			{

ICSharpCode.Decompiler/CSharp/Transforms/DeclareVariables.cs

@@ -19,6 +19,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 
 using ICSharpCode.Decompiler.CSharp.Syntax;
@@ -552,7 +553,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			}
 		}
 
-		bool IsMatchingAssignment(VariableToDeclare v, out AssignmentExpression assignment)
+		bool IsMatchingAssignment(VariableToDeclare v, [NotNullWhen(true)] out AssignmentExpression? assignment)
 		{
 			assignment = v.InsertionPoint.nextNode as AssignmentExpression;
 			if (assignment == null)
@@ -731,7 +732,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			}
 		}
 
-		private bool CanBeDeclaredAsOutVariable(VariableToDeclare v, out DirectionExpression dirExpr)
+		private bool CanBeDeclaredAsOutVariable(VariableToDeclare v, [NotNullWhen(true)] out DirectionExpression? dirExpr)
 		{
 			dirExpr = v.FirstUse.Parent as DirectionExpression;
 			if (dirExpr == null || dirExpr.FieldDirection != FieldDirection.Out)
@@ -740,7 +741,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 				return false;
 			if (v.DefaultInitialization != VariableInitKind.None)
 				return false;
-			for (AstNode node = v.FirstUse; node != null; node = node.Parent)
+			for (AstNode? node = v.FirstUse; node != null; node = node.Parent)
 			{
 				if (node.Role == Roles.EmbeddedStatement)
 				{

ICSharpCode.Decompiler/CSharp/Transforms/IntroduceQueryExpressions.cs

@@ -18,6 +18,7 @@
 
 using System;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 
 using ICSharpCode.Decompiler.CSharp.Syntax;
@@ -370,7 +371,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 		}
 
 		/// <summary>Matches simple lambdas of the form "a => b"</summary>
-		bool MatchSimpleLambda(Expression expr, out ParameterDeclaration? parameter, out Expression? body)
+		bool MatchSimpleLambda(Expression expr, [NotNullWhen(true)] out ParameterDeclaration? parameter, [NotNullWhen(true)] out Expression? body)
 		{
 			if (expr is LambdaExpression lambda && lambda.Parameters.Count == 1 && lambda.Body is Expression)
 			{

ICSharpCode.Decompiler/CSharp/Transforms/PatternStatementTransform.cs

@@ -19,6 +19,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 
 using ICSharpCode.Decompiler.CSharp.Syntax;
@@ -431,7 +432,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 				)
 			)));
 
-		bool MatchLowerBound(int indexNum, out IL.ILVariable? index, IL.ILVariable collection, Statement statement)
+		bool MatchLowerBound(int indexNum, [NotNullWhen(true)] out IL.ILVariable? index, IL.ILVariable collection, Statement statement)
 		{
 			index = null;
 			var m = variableAssignLowerBoundPattern.Match(statement);
@@ -443,7 +444,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			return m.Get<IdentifierExpression>("collection").Single().GetILVariable() == collection;
 		}
 
-		bool MatchForeachOnMultiDimArray(IL.ILVariable[] upperBounds, IL.ILVariable collection, Statement firstInitializerStatement, out IdentifierExpression? foreachVariable, out IList<Statement>? statements, out IL.ILVariable[] lowerBounds)
+		bool MatchForeachOnMultiDimArray(IL.ILVariable[] upperBounds, IL.ILVariable collection, Statement firstInitializerStatement, [NotNullWhen(true)] out IdentifierExpression? foreachVariable, [NotNullWhen(true)] out IList<Statement>? statements, out IL.ILVariable[] lowerBounds)
 		{
 			int i = 0;
 			foreachVariable = null;
@@ -451,7 +452,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			lowerBounds = new IL.ILVariable[upperBounds.Length];
 			Statement stmt = firstInitializerStatement;
 			Match m = default(Match);
-			while (i < upperBounds.Length && MatchLowerBound(i, out IL.ILVariable indexVariable, collection, stmt))
+			while (i < upperBounds.Length && MatchLowerBound(i, out IL.ILVariable? indexVariable, collection, stmt))
 			{
 				m = forOnArrayMultiDimPattern.Match(stmt.GetNextStatement());
 				if (!m.Success)
@@ -702,16 +703,16 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			return base.VisitIdentifier(identifier);
 		}
 
-		internal static bool IsBackingFieldOfAutomaticProperty(IField field, out IProperty? property)
+		internal static bool IsBackingFieldOfAutomaticProperty(IField field, [NotNullWhen(true)] out IProperty? property)
 		{
 			property = null;
-			if (!NameCouldBeBackingFieldOfAutomaticProperty(field.Name, out string propertyName))
+			if (!NameCouldBeBackingFieldOfAutomaticProperty(field.Name, out string? propertyName))
 				return false;
 			if (!field.IsCompilerGenerated())
 				return false;
-			property = field.DeclaringTypeDefinition
+			property = field.DeclaringTypeDefinition?
 				.GetProperties(p => p.Name == propertyName, GetMemberOptions.IgnoreInheritedMembers)
-				.FirstOrDefault();
+				?.FirstOrDefault();
 			return property != null;
 		}
 
@@ -725,7 +726,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 		static readonly System.Text.RegularExpressions.Regex automaticPropertyBackingFieldNameRegex
 			= new System.Text.RegularExpressions.Regex(@"^(<(?<name>.+)>k__BackingField|_(?<name>.+))$");
 
-		static bool NameCouldBeBackingFieldOfAutomaticProperty(string name, out string? propertyName)
+		static bool NameCouldBeBackingFieldOfAutomaticProperty(string name, [NotNullWhen(true)] out string? propertyName)
 		{
 			propertyName = null;
 			var m = automaticPropertyBackingFieldNameRegex.Match(name);

ICSharpCode.Decompiler/DebugInfo/IDebugInfoProvider.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Reflection.Metadata;
 using System.Text;
 
@@ -28,8 +29,8 @@ namespace ICSharpCode.Decompiler.DebugInfo
 		string Description { get; }
 		IList<SequencePoint> GetSequencePoints(MethodDefinitionHandle method);
 		IList<Variable> GetVariables(MethodDefinitionHandle method);
-		bool TryGetName(MethodDefinitionHandle method, int index, out string name);
-		bool TryGetExtraTypeInfo(MethodDefinitionHandle method, int index, out PdbExtraTypeInfo extraTypeInfo);
+		bool TryGetName(MethodDefinitionHandle method, int index, [NotNullWhen(true)] out string? name);
+		bool TryGetExtraTypeInfo(MethodDefinitionHandle method, int index, [NotNullWhen(true)] out PdbExtraTypeInfo extraTypeInfo);
 		string SourceFileName { get; }
 	}
 }

ICSharpCode.Decompiler/DecompilerSettings.cs

@@ -2173,7 +2173,7 @@ namespace ICSharpCode.Decompiler
 			}
 		}
 
-		public event PropertyChangedEventHandler PropertyChanged;
+		public event PropertyChangedEventHandler? PropertyChanged;
 
 		protected virtual void OnPropertyChanged([CallerMemberName] string? propertyName = null)
 		{

ICSharpCode.Decompiler/IL/ControlFlow/AsyncAwaitDecompiler.cs

@@ -20,6 +20,7 @@ using System;
 using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Reflection.Metadata;
 
@@ -482,7 +483,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 		/// <summary>
 		/// Matches a (potentially virtual) instance method call.
 		/// </summary>
-		static bool MatchCall(ILInstruction inst, string name, out InstructionCollection<ILInstruction>? args)
+		static bool MatchCall(ILInstruction inst, string name, [NotNullWhen(true)] out InstructionCollection<ILInstruction>? args)
 		{
 			if (inst is CallInstruction call && (call.OpCode == OpCode.Call || call.OpCode == OpCode.CallVirt)
 				&& call.Method.Name == name && !call.Method.IsStatic)
@@ -497,7 +498,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 		/// <summary>
 		/// Matches a store to the state machine.
 		/// </summary>
-		static bool MatchStFld(ILInstruction stfld, ILVariable stateMachineVar, out IField field, out ILInstruction value)
+		static bool MatchStFld(ILInstruction stfld, ILVariable stateMachineVar, [NotNullWhen(true)] out IField? field, [NotNullWhen(true)] out ILInstruction? value)
 		{
 			if (!stfld.MatchStFld(out var target, out field, out value))
 				return false;
@@ -869,7 +870,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			return blockContainer.Blocks[setResultReturnBlockIndex];
 		}
 
-		private bool MatchDisposeCombinedTokens(BlockContainer blockContainer, ILInstruction condition, ILInstruction trueInst, ILInstruction falseInst, bool[] blocksAnalyzed, out Block? setResultAndExitBlock)
+		private bool MatchDisposeCombinedTokens(BlockContainer blockContainer, ILInstruction condition, ILInstruction trueInst, ILInstruction falseInst, bool[] blocksAnalyzed, [NotNullWhen(true)] out Block? setResultAndExitBlock)
 		{
 			setResultAndExitBlock = null;
 			// 	...
@@ -1423,7 +1424,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			}
 		}
 
-		bool AnalyzeAwaitBlock(Block block, out ILVariable? awaiter, out IField? awaiterField, out int state, out int yieldOffset)
+		bool AnalyzeAwaitBlock(Block block, [NotNullWhen(true)] out ILVariable? awaiter, [NotNullWhen(true)] out IField? awaiterField, out int state, out int yieldOffset)
 		{
 			awaiter = null;
 			awaiterField = null;
@@ -1522,6 +1523,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			{
 				pos--;
 			}
+
 			block.Instructions.RemoveRange(pos, block.Instructions.Count - pos);
 			return true;
 		}
@@ -1538,7 +1540,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			return inst;
 		}
 
-		private bool AnalyzeYieldReturn(Block block, out ILInstruction? yieldValue, out int newState)
+		private bool AnalyzeYieldReturn(Block block, [NotNullWhen(true)] out ILInstruction? yieldValue, out int newState)
 		{
 			yieldValue = default;
 			newState = default;
@@ -1584,7 +1586,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			return true;
 		}
 
-		bool MatchCurrentAssignment(ILInstruction inst, out ILInstruction value)
+		bool MatchCurrentAssignment(ILInstruction inst, [NotNullWhen(true)] out ILInstruction? value)
 		{
 			if (!inst.MatchStFld(out var target, out var field, out value))
 				return false;
@@ -1701,7 +1703,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			return inst;
 		}
 
-		bool CheckAwaitBlock(Block block, out Block? resumeBlock, out IField? stackField)
+		bool CheckAwaitBlock(Block block, [NotNullWhen(true)] out Block? resumeBlock, out IField? stackField)
 		{
 			// awaitBlock:
 			//   (pre-roslyn: save stack)

ICSharpCode.Decompiler/IL/ControlFlow/AwaitInCatchTransform.cs

@@ -19,6 +19,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 
 using ICSharpCode.Decompiler.IL.Transforms;
@@ -223,7 +224,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 		/// Analyzes all catch handlers and returns every handler that follows the await catch handler pattern.
 		/// </summary>
 		static bool AnalyzeHandlers(InstructionCollection<TryCatchHandler> handlers, out ILVariable? catchHandlerIdentifier,
-			out List<CatchBlockInfo> transformableCatchBlocks)
+			[NotNullWhen(true)] out List<CatchBlockInfo> transformableCatchBlocks)
 		{
 			transformableCatchBlocks = new List<CatchBlockInfo>();
 			catchHandlerIdentifier = null;
@@ -254,9 +255,9 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 		/// stloc V_5(ldc.i4 2)		- store id of catch block in 'identifierVariable'
 		/// br IL_0075				- jump out of catch block to the head of the catch-handler jump table
 		/// </summary>
-		static bool MatchAwaitCatchHandler(TryCatchHandler handler, out int id, out ILVariable? identifierVariable,
-			out Block? realEntryPoint, out ILInstruction? nextBlockOrExitContainer,
-			out ILInstruction? jumpTableEntry, out ILVariable? objectVariable)
+		static bool MatchAwaitCatchHandler(TryCatchHandler handler, out int id, [NotNullWhen(true)] out ILVariable? identifierVariable,
+			[NotNullWhen(true)] out Block? realEntryPoint, out ILInstruction? nextBlockOrExitContainer,
+			[NotNullWhen(true)] out ILInstruction? jumpTableEntry, out ILVariable? objectVariable)
 		{
 			id = 0;
 			identifierVariable = null;
@@ -266,7 +267,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			nextBlockOrExitContainer = null;
 			var exceptionVariable = handler.Variable;
 			var catchBlock = ((BlockContainer)handler.Body).EntryPoint;
-			ILInstruction value;
+			ILInstruction? value;
 			switch (catchBlock.Instructions.Count)
 			{
 				case 3:
@@ -326,7 +327,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 					return false;
 			}
 
-			bool ParseSwitchJumpTable(int id, SwitchInstruction jumpTable, ILVariable identifierVariable, out Block? realEntryPoint, out ILInstruction? nextBlockOrExitContainer, out ILInstruction? jumpTableEntry)
+			bool ParseSwitchJumpTable(int id, SwitchInstruction jumpTable, ILVariable identifierVariable, [NotNullWhen(true)] out Block? realEntryPoint, out ILInstruction? nextBlockOrExitContainer, [NotNullWhen(true)] out ILInstruction? jumpTableEntry)
 			{
 				realEntryPoint = null;
 				nextBlockOrExitContainer = null;

ICSharpCode.Decompiler/IL/ControlFlow/ConditionDetection.cs

@@ -18,6 +18,7 @@
 
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 
 using ICSharpCode.Decompiler.FlowAnalysis;
@@ -610,7 +611,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 		/// Determine if the specified instruction necessarily exits (EndPointUnreachable)
 		/// and if so return last (or single) exit instruction
 		/// </summary>
-		private static bool TryGetExit(ILInstruction inst, out ILInstruction? exitInst)
+		private static bool TryGetExit(ILInstruction inst, [NotNullWhen(true)] out ILInstruction? exitInst)
 		{
 			if (inst is Block block && block.Instructions.Count > 0)
 				inst = block.Instructions.Last();

ICSharpCode.Decompiler/IL/ControlFlow/DetectPinnedRegions.cs

@@ -18,6 +18,7 @@
 
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Runtime.InteropServices.ComTypes;
 
@@ -241,8 +242,8 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 		//      stloc V_1(get.pinnable.reference(ldloc mem))
 		//      stloc ptr(conv ref->u (ldloc V_1))
 		//      br targetBlock
-		private bool IsCustomRefPinPattern(Block block, out ILInstruction? ldlocMem, out CallInstruction? callGPR,
-			out ILVariable? v, out StLoc? ptrAssign, out Block? targetBlock, out Block? nullBlock, out Block? notNullBlock)
+		private bool IsCustomRefPinPattern(Block block, [NotNullWhen(true)] out ILInstruction? ldlocMem, [NotNullWhen(true)] out CallInstruction? callGPR,
+			[NotNullWhen(true)] out ILVariable? v, out StLoc? ptrAssign, [NotNullWhen(true)] out Block? targetBlock, out Block? nullBlock, [NotNullWhen(true)] out Block? notNullBlock)
 		{
 			ldlocMem = null;
 			callGPR = null;
@@ -356,7 +357,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 		//   ...
 		//   stloc P(array.to.pointer(V))
 		//   br B_target
-		bool IsNullSafeArrayToPointerPattern(Block block, out ILVariable? v, out ILVariable? p, out Block? targetBlock)
+		bool IsNullSafeArrayToPointerPattern(Block block, [NotNullWhen(true)] out ILVariable? v, [NotNullWhen(true)] out ILVariable? p, [NotNullWhen(true)] out Block? targetBlock)
 		{
 			v = null;
 			p = null;
@@ -384,7 +385,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 					usingPreviousVar = true;
 				}
 			}
-			if (!ifInst.TrueInst.MatchBranch(out Block nullOrEmptyBlock))
+			if (!ifInst.TrueInst.MatchBranch(out Block? nullOrEmptyBlock))
 				return false;
 			if (!ifInst.FalseInst.MatchNop())
 				return false;
@@ -394,7 +395,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 				return false;
 			if (!(p.Kind == VariableKind.PinnedLocal || (usingPreviousVar && v.Kind == VariableKind.PinnedLocal)))
 				return false;
-			if (!block.Instructions.Last().MatchBranch(out Block notNullBlock))
+			if (!block.Instructions.Last().MatchBranch(out Block? notNullBlock))
 				return false;
 			if (notNullBlock.Parent != block.Parent)
 				return false;
@@ -409,7 +410,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			// }
 			if (block.Instructions.Count != 2)
 				return false;
-			if (!block.Instructions[0].MatchIfInstruction(out ILInstruction condition, out ILInstruction trueInst))
+			if (!block.Instructions[0].MatchIfInstruction(out var condition, out var trueInst))
 				return false;
 			var falseInst = block.Instructions[1];
 			if (condition is Comp comp && comp.Right.MatchLdcI(0))
@@ -495,7 +496,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			return block.Instructions[1].MatchBranch(targetBlock);
 		}
 
-		bool IsNullSafeArrayToPointerNullOrEmptyBlock(Block block, out ILVariable? p, out Block? targetBlock)
+		bool IsNullSafeArrayToPointerNullOrEmptyBlock(Block block, [NotNullWhen(true)] out ILVariable? p, [NotNullWhen(true)] out Block? targetBlock)
 		{
 			p = null;
 			targetBlock = null;
@@ -503,7 +504,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			//   stloc P(conv i4->u(ldc.i4 0))
 			//   br B_target
 			// }
-			ILInstruction value;
+			ILInstruction? value;
 			return block.Instructions.Count == 2
 				&& block.Instructions[0].MatchStLoc(out p, out value)
 				&& (p.Kind == VariableKind.PinnedLocal || p.Kind == VariableKind.Local)
@@ -863,13 +864,12 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			return slotInfo == Block.InstructionSlot || slotInfo == LdObj.TargetSlot || slotInfo == StObj.TargetSlot;
 		}
 
-		bool IsBranchOnNull(ILInstruction condBranch, ILVariable nativeVar, out Block? targetBlock)
+		bool IsBranchOnNull(ILInstruction condBranch, ILVariable nativeVar, [NotNullWhen(true)] out Block? targetBlock)
 		{
 			targetBlock = null;
 			// if (comp(ldloc nativeVar == conv i4->i <sign extend>(ldc.i4 0))) br targetBlock
-			ILInstruction condition, trueInst, left, right;
-			return condBranch.MatchIfInstruction(out condition, out trueInst)
-				&& condition.MatchCompEquals(out left, out right)
+			return condBranch.MatchIfInstruction(out var condition, out var trueInst)
+				&& condition.MatchCompEquals(out var left, out var right)
 				&& left.MatchLdLoc(nativeVar) && IsNullOrZero(right)
 				&& trueInst.MatchBranch(out targetBlock);
 		}
@@ -884,7 +884,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			// if (comp(ldloc nativeVar == conv i4->i <sign extend>(ldc.i4 0))) br targetBlock
 			// br adjustOffsetToStringData
 			ILVariable newVar;
-			if (!body.EntryPoint.Instructions[0].MatchStLoc(out ILVariable nativeVar, out ILInstruction initInst))
+			if (!body.EntryPoint.Instructions[0].MatchStLoc(out var nativeVar, out var initInst))
 			{
 				// potentially a special case with legacy csc and an unused pinned variable:
 				if (pinnedRegion.Variable.AddressCount == 0 && pinnedRegion.Variable.LoadCount == 0)
@@ -902,11 +902,11 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			if (nativeVar.Type.GetStackType() != StackType.I)
 				return;
 
-			Block targetBlock;
+			Block? targetBlock;
 			Block? adjustOffsetToStringData = null;
 			if (body.EntryPoint.Instructions.Count == 2)
 			{
-				if (!initInst.MatchBinaryNumericInstruction(BinaryNumericOperator.Add, out ILInstruction left, out ILInstruction right))
+				if (!initInst.MatchBinaryNumericInstruction(BinaryNumericOperator.Add, out var left, out var right))
 					return;
 				if (!left.UnwrapConv(ConversionKind.StopGCTracking).MatchLdLoc(pinnedRegion.Variable))
 					return;
@@ -977,13 +977,13 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			ReplacePinnedVar(pinnedRegion.Variable, newVar, pinnedRegion);
 		}
 
-		bool IsOffsetToStringDataBlock(Block block, ILVariable nativeVar, Block targetBlock)
+		bool IsOffsetToStringDataBlock(Block block, ILVariable nativeVar, Block? targetBlock)
 		{
 			// stloc nativeVar(add(ldloc nativeVar, conv i4->i <sign extend>(call [Accessor System.Runtime.CompilerServices.RuntimeHelpers.get_OffsetToStringData():System.Int32]())))
 			// br IL_0011
 			if (block.Instructions.Count != 2)
 				return false;
-			ILInstruction value;
+			ILInstruction? value;
 			if (nativeVar.IsSingleDefinition && nativeVar.LoadCount == 2)
 			{
 				// If there are no loads (except for the two in the string-to-pointer pattern),
@@ -1003,7 +1003,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			{
 				return false;
 			}
-			if (!value.MatchBinaryNumericInstruction(BinaryNumericOperator.Add, out ILInstruction left, out ILInstruction right))
+			if (!value.MatchBinaryNumericInstruction(BinaryNumericOperator.Add, out var left, out var right))
 				return false;
 			if (!left.MatchLdLoc(nativeVar))
 				return false;

ICSharpCode.Decompiler/IL/ControlFlow/LoopDetection.cs

@@ -613,6 +613,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 				// skip blocks that only branch to another block
 				entryPoint = targetBlock;
 			}
+
 			return entryPoint == loopHead;
 		}
 		#endregion

ICSharpCode.Decompiler/IL/ControlFlow/SwitchAnalysis.cs

@@ -314,7 +314,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 				trueValues = new LongSet(0).Invert();
 				return true;
 			}
-			else if (condition.MatchLogicNot(out ILInstruction arg))
+			else if (condition.MatchLogicNot(out var arg))
 			{
 				// if (logic.not(X)) --> branch for all values where if (X) does not branch
 				bool res = AnalyzeCondition(arg, out LongSet falseValues);

ICSharpCode.Decompiler/IL/ControlFlow/YieldReturnDecompiler.cs

@@ -19,6 +19,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Reflection.Metadata;
 
@@ -1426,7 +1427,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			}
 			context.StepEndGroup(keepIfEmpty: true);
 
-			bool IsCallToMonoFinallyMethod(Call call, out IMethod? finallyMethod)
+			bool IsCallToMonoFinallyMethod(Call call, [NotNullWhen(true)] out IMethod? finallyMethod)
 			{
 				finallyMethod = default;
 				if (call == null)

ICSharpCode.Decompiler/IL/ILReader.cs

@@ -312,7 +312,7 @@ namespace ICSharpCode.Decompiler.IL
 			}
 
 			ILVariable ilVar = new ILVariable(kind, type, index);
-			if (!UseDebugSymbols || DebugInfo == null || !DebugInfo.TryGetName((MethodDefinitionHandle)method.MetadataToken, index, out string name))
+			if (!UseDebugSymbols || DebugInfo == null || !DebugInfo.TryGetName((MethodDefinitionHandle)method.MetadataToken, index, out string? name))
 			{
 				ilVar.Name = "V_" + index;
 				ilVar.HasGeneratedName = true;

ICSharpCode.Decompiler/IL/Instructions/DeconstructInstruction.cs

@@ -19,6 +19,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 
 using ICSharpCode.Decompiler.TypeSystem;
@@ -190,7 +191,7 @@ namespace ICSharpCode.Decompiler.IL
 			output.MarkFoldEnd();
 		}
 
-		internal static bool IsConversionStLoc(ILInstruction inst, out ILVariable variable, out ILVariable? inputVariable)
+		internal static bool IsConversionStLoc(ILInstruction inst, [NotNullWhen(true)] out ILVariable? variable, [NotNullWhen(true)] out ILVariable? inputVariable)
 		{
 			inputVariable = null;
 			if (!inst.MatchStLoc(out variable, out var value))
@@ -210,7 +211,7 @@ namespace ICSharpCode.Decompiler.IL
 			return input.MatchLdLoc(out inputVariable) || input.MatchLdLoca(out inputVariable);
 		}
 
-		internal static bool IsAssignment(ILInstruction inst, ICompilation typeSystem, out IType? expectedType, out ILInstruction? value)
+		internal static bool IsAssignment(ILInstruction inst, ICompilation typeSystem, [NotNullWhen(true)] out IType? expectedType, [NotNullWhen(true)] out ILInstruction? value)
 		{
 			expectedType = null;
 			value = null;

ICSharpCode.Decompiler/IL/Transforms/DeconstructionTransform.cs

@@ -19,6 +19,7 @@
 using System;
 using System.Collections.Generic;
 using System.Collections.Immutable;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Resources;
 
@@ -35,9 +36,9 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 	{
 		StatementTransformContext context;
 		readonly Dictionary<ILVariable, int> deconstructionResultsLookup = new Dictionary<ILVariable, int>();
-		ILVariable[] deconstructionResults;
-		ILVariable tupleVariable;
-		TupleType tupleType;
+		ILVariable[]? deconstructionResults;
+		ILVariable? tupleVariable;
+		TupleType? tupleType;
 
 		/*
 			stloc tuple(call MakeIntIntTuple(ldloc this))
@@ -262,8 +263,8 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return true;
 		}
 
-		bool MatchDeconstruction(ILInstruction inst, out IMethod? deconstructMethod,
-			out ILInstruction? testedOperand)
+		bool MatchDeconstruction(ILInstruction inst, [NotNullWhen(true)] out IMethod? deconstructMethod,
+			[NotNullWhen(true)] out ILInstruction? testedOperand)
 		{
 			testedOperand = null;
 			deconstructMethod = null;
@@ -328,8 +329,8 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return true;
 		}
 
-		bool MatchConversion(ILInstruction inst, out ILInstruction? inputInstruction,
-			out ILVariable outputVariable, out ConversionInfo info)
+		bool MatchConversion(ILInstruction inst, [NotNullWhen(true)] out ILInstruction? inputInstruction,
+			[NotNullWhen(true)] out ILVariable? outputVariable, [NotNullWhen(true)] out ConversionInfo info)
 		{
 			info = default;
 			inputInstruction = null;
@@ -433,7 +434,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			}
 		}
 
-		bool MatchAssignment(ILInstruction inst, out IType? targetType, out ILInstruction? valueInst, out Action<DeconstructInstruction>? addAssignment)
+		bool MatchAssignment(ILInstruction inst, out IType? targetType, [NotNullWhen(true)] out ILInstruction? valueInst, [NotNullWhen(true)] out Action<DeconstructInstruction>? addAssignment)
 		{
 			targetType = null;
 			valueInst = null;

ICSharpCode.Decompiler/IL/Transforms/DelegateConstruction.cs

@@ -17,6 +17,7 @@
 // DEALINGS IN THE SOFTWARE.
 
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Reflection.Metadata;
 
@@ -80,7 +81,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		}
 
 		internal static bool MatchDelegateConstruction(ILInstruction inst, out IMethod? targetMethod,
-			out ILInstruction? target, out IType? delegateType, bool allowTransformed = false)
+			[NotNullWhen(true)] out ILInstruction? target, [NotNullWhen(true)] out IType? delegateType, bool allowTransformed = false)
 		{
 			targetMethod = null;
 			target = null;

ICSharpCode.Decompiler/IL/Transforms/DetectCatchWhenConditionBlocks.cs

@@ -19,6 +19,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 
 using ICSharpCode.Decompiler.TypeSystem;
@@ -162,7 +163,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		///   br falseBlock
 		/// }
 		/// </summary>
-		bool MatchCatchWhenEntryPoint(ILVariable exceptionVar, BlockContainer container, Block entryPoint, out IType? exceptionType, out ILInstruction? exceptionSlot, out Block? whenConditionBlock)
+		bool MatchCatchWhenEntryPoint(ILVariable exceptionVar, BlockContainer container, Block entryPoint, [NotNullWhen(true)] out IType? exceptionType, [NotNullWhen(true)] out ILInstruction? exceptionSlot, [NotNullWhen(true)] out Block? whenConditionBlock)
 		{
 			exceptionType = null;
 			exceptionSlot = null;
@@ -206,6 +207,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					return false;
 				if (right.MatchLdNull())
 				{
+
 					return branch.MatchBranch(out whenConditionBlock);
 				}
 			}
@@ -218,7 +220,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		///   br exitBlock
 		/// }
 		/// </summary>
-		bool MatchFalseBlock(BlockContainer container, Block falseBlock, out ILVariable? returnVar, out Block? exitBlock)
+		bool MatchFalseBlock(BlockContainer container, Block falseBlock, [NotNullWhen(true)] out ILVariable? returnVar, [NotNullWhen(true)] out Block? exitBlock)
 		{
 			returnVar = null;
 			exitBlock = null;

ICSharpCode.Decompiler/IL/Transforms/DynamicCallSiteTransform.cs

@@ -19,6 +19,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Linq.Expressions;
 
@@ -272,7 +273,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			}
 		}
 
-		bool ScanCallSiteInitBlock(Block callSiteInitBlock, IField callSiteCacheField, IType callSiteDelegateType, out CallSiteInfo callSiteInfo, out Block? blockAfterInit)
+		bool ScanCallSiteInitBlock(Block callSiteInitBlock, IField callSiteCacheField, IType callSiteDelegateType, out CallSiteInfo callSiteInfo, [NotNullWhen(true)] out Block? blockAfterInit)
 		{
 			callSiteInfo = default(CallSiteInfo);
 			blockAfterInit = null;
@@ -300,7 +301,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					if (!binderCall.Arguments[0].MatchLdcI4(out int binderFlagsInteger))
 						return false;
 					callSiteInfo.Flags = (CSharpBinderFlags)binderFlagsInteger;
-					if (!binderCall.Arguments[1].MatchLdStr(out string name))
+					if (!binderCall.Arguments[1].MatchLdStr(out var name))
 						return false;
 					callSiteInfo.MemberName = name;
 					if (!TransformExpressionTrees.MatchGetTypeFromHandle(binderCall.Arguments[2], out var contextType))
@@ -551,7 +552,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					return false;
 				if (!createCall.Arguments[0].MatchLdcI4(out var argumentInfoFlags))
 					return false;
-				if (!createCall.Arguments[1].MatchLdStr(out string argumentName))
+				if (!createCall.Arguments[1].MatchLdStr(out var argumentName))
 					if (!createCall.Arguments[1].MatchLdNull())
 						return false;
 				callSiteInfo.ArgumentInfos[i] = new CSharpArgumentInfo { Flags = (CSharpArgumentInfoFlags)argumentInfoFlags, Name = argumentName, CompileTimeType = compileTimeTypes[i + 1] };
@@ -560,7 +561,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return true;
 		}
 
-		bool MatchCallSiteCacheNullCheck(ILInstruction condition, out IField? callSiteCacheField, out IType? callSiteDelegate, out bool invertBranches)
+		bool MatchCallSiteCacheNullCheck(ILInstruction condition, [NotNullWhen(true)] out IField? callSiteCacheField, [NotNullWhen(true)] out IType? callSiteDelegate, out bool invertBranches)
 		{
 			callSiteCacheField = null;
 			callSiteDelegate = null;

ICSharpCode.Decompiler/IL/Transforms/DynamicIsEventAssignmentTransform.cs

@@ -16,6 +16,7 @@
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
 
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 
 namespace ICSharpCode.Decompiler.IL.Transforms
@@ -121,7 +122,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// 	stloc V_2(dynamic.getmember B(target))
 		/// }
 		/// </summary>
-		static bool MatchLhsCacheIfInstruction(ILInstruction ifInst, ILVariable flagVar, out StLoc? cacheStore)
+		static bool MatchLhsCacheIfInstruction(ILInstruction ifInst, ILVariable flagVar, [NotNullWhen(true)] out StLoc? cacheStore)
 		{
 			cacheStore = null;
 			if (!ifInst.MatchIfInstruction(out var condition, out var trueInst))

ICSharpCode.Decompiler/IL/Transforms/EarlyExpressionTransforms.cs

@@ -16,6 +16,7 @@
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
 
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 
 using ICSharpCode.Decompiler.TypeSystem;
@@ -175,7 +176,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 
 		protected internal override void VisitNewObj(NewObj inst)
 		{
-			if (TransformDecimalCtorToConstant(inst, out LdcDecimal decimalConstant))
+			if (TransformDecimalCtorToConstant(inst, out var decimalConstant))
 			{
 				context.Step("TransformDecimalCtorToConstant", inst);
 				inst.ReplaceWith(decimalConstant);
@@ -185,7 +186,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			base.VisitNewObj(inst);
 		}
 
-		bool TransformDecimalCtorToConstant(NewObj inst, out LdcDecimal? result)
+		bool TransformDecimalCtorToConstant(NewObj inst, [NotNullWhen(true)] out LdcDecimal? result)
 		{
 			IType t = inst.Method.DeclaringType;
 			result = null;

ICSharpCode.Decompiler/IL/Transforms/ExpressionTransforms.cs

@@ -19,6 +19,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Linq.Expressions;
 
@@ -342,7 +343,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// =>
 		/// ldvirtdelegate System.Delegate TargetMethod(target)
 		/// </summary>
-		bool TransformDelegateCtorLdVirtFtnToLdVirtDelegate(NewObj inst, out LdVirtDelegate? ldVirtDelegate)
+		bool TransformDelegateCtorLdVirtFtnToLdVirtDelegate(NewObj inst, [NotNullWhen(true)] out LdVirtDelegate? ldVirtDelegate)
 		{
 			ldVirtDelegate = null;
 			if (inst.Method.DeclaringType.Kind != TypeKind.Delegate)
@@ -379,7 +380,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		///		final: ldloc I_0
 		/// }
 		/// </summary>
-		bool TransformSpanTCtorContainingStackAlloc(NewObj newObj, out ILInstruction? locallocSpan)
+		bool TransformSpanTCtorContainingStackAlloc(NewObj newObj, [NotNullWhen(true)] out ILInstruction? locallocSpan)
 		{
 			locallocSpan = null;
 			IType type = newObj.Method.DeclaringType;
@@ -428,7 +429,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return true;
 		}
 
-		bool TransformDecimalFieldToConstant(LdObj inst, out LdcDecimal? result)
+		bool TransformDecimalFieldToConstant(LdObj inst, [NotNullWhen(true)] out LdcDecimal? result)
 		{
 			if (inst.MatchLdsFld(out var field) && field.DeclaringType.IsKnownType(KnownTypeCode.Decimal))
 			{

ICSharpCode.Decompiler/IL/Transforms/HighLevelLoopTransform.cs

@@ -19,6 +19,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 
 using ICSharpCode.Decompiler.IL.ControlFlow;
@@ -53,7 +54,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			}
 		}
 
-		bool MatchWhileLoop(BlockContainer loop, out IfInstruction? condition, out Block loopBody)
+		bool MatchWhileLoop(BlockContainer loop, [NotNullWhen(true)] out IfInstruction? condition, out Block loopBody)
 		{
 			// ConditionDetection favours leave inside if and branch at end of block
 			// while-loop:
@@ -115,7 +116,6 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					ExpressionTransforms.RunOnSingleStatment(inst, context);
 				}
 			}*/
-
 			return true;
 		}
 
@@ -156,7 +156,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// </summary>
 		bool MatchDoWhileLoop(BlockContainer loop)
 		{
-			(List<IfInstruction> conditions, ILInstruction exit, bool swap, bool split, bool unwrap) = AnalyzeDoWhileConditions(loop);
+			(List<IfInstruction>? conditions, ILInstruction exit, bool swap, bool split, bool unwrap) = AnalyzeDoWhileConditions(loop);
 			// not a do-while loop, exit.
 			if (conditions == null || conditions.Count == 0)
 				return false;
@@ -240,7 +240,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return true;
 		}
 
-		static (List<IfInstruction> conditions, ILInstruction exit, bool swap, bool split, bool unwrap) AnalyzeDoWhileConditions(BlockContainer loop)
+		static (List<IfInstruction>? conditions, ILInstruction? exit, bool swap, bool split, bool unwrap) AnalyzeDoWhileConditions(BlockContainer loop)
 		{
 			// we iterate over all blocks from the bottom, because the entry-point
 			// should only be considered as condition block, if there are no other blocks.
@@ -356,7 +356,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		}
 
 		// early match before block containers have been constructed
-		internal static bool MatchDoWhileConditionBlock(Block block, out Block target1, out Block? target2)
+		internal static bool MatchDoWhileConditionBlock(Block block, out Block? target1, out Block? target2)
 		{
 			target1 = target2 = null;
 			if (block.Instructions.Count < 2)
@@ -370,7 +370,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				   (last.MatchBranch(out target2) || last.MatchReturn(out var _));
 		}
 
-		internal static Block GetIncrementBlock(BlockContainer loop, Block whileLoopBody) =>
+		internal static Block? GetIncrementBlock(BlockContainer loop, Block whileLoopBody) =>
 			loop.Blocks.SingleOrDefault(b => b != whileLoopBody
 										  && b.Instructions.Last().MatchBranch(loop.EntryPoint)
 										  && b.Instructions.SkipLast(1).All(IsSimpleStatement));
@@ -480,7 +480,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// Returns true if the instruction is stloc v(add(ldloc v, arg))
 		/// or compound.assign(ldloca v, arg)
 		/// </summary>
-		public static bool MatchIncrement(ILInstruction inst, out ILVariable variable)
+		public static bool MatchIncrement(ILInstruction inst, [NotNullWhen(true)] out ILVariable? variable)
 		{
 			if (inst.MatchStLoc(out variable, out var value))
 			{

ICSharpCode.Decompiler/IL/Transforms/IndexRangeTransform.cs

@@ -17,6 +17,7 @@
 // DEALINGS IN THE SOFTWARE.
 
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 
 using ICSharpCode.Decompiler.TypeSystem;
@@ -152,7 +153,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			int startPos = pos;
 			ILVariable? containerVar = null;
 			// The container length access may be a separate instruction, or it may be inline with the variable's use
-			if (MatchContainerLengthStore(block.Instructions[pos], out ILVariable containerLengthVar, ref containerVar))
+			if (MatchContainerLengthStore(block.Instructions[pos], out var containerLengthVar, ref containerVar))
 			{
 				//  stloc containerLengthVar(call get_Length/get_Count(ldloc container))
 				pos++;
@@ -465,7 +466,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			}
 		}
 
-		private bool MatchIndexImplicitConv(ILInstruction inst, out ILInstruction? offsetInst)
+		private bool MatchIndexImplicitConv(ILInstruction inst, [NotNullWhen(true)] out ILInstruction? offsetInst)
 		{
 			offsetInst = null;
 			if (!(inst is CallInstruction call))
@@ -607,7 +608,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// Matches the instruction:
 		///    stloc containerLengthVar(call get_Length/get_Count(ldloc containerVar))
 		/// </summary>
-		static bool MatchContainerLengthStore(ILInstruction inst, out ILVariable lengthVar, ref ILVariable containerVar)
+		static bool MatchContainerLengthStore(ILInstruction inst, [NotNullWhen(true)] out ILVariable? lengthVar, ref ILVariable? containerVar)
 		{
 			if (!inst.MatchStLoc(out lengthVar, out var init))
 				return false;
@@ -624,7 +625,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		///	Otherwise, matches the instruction:
 		///		call get_Length/get_Count(ldloc containerVar)
 		/// </summary>
-		static bool MatchContainerLength(ILInstruction init, ILVariable lengthVar, ref ILVariable containerVar)
+		static bool MatchContainerLength(ILInstruction init, ILVariable? lengthVar, ref ILVariable? containerVar)
 		{
 			if (lengthVar != null)
 			{
@@ -658,7 +659,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return MatchContainerVar(call.Arguments[0], ref containerVar);
 		}
 
-		static bool MatchContainerVar(ILInstruction inst, ref ILVariable containerVar)
+		static bool MatchContainerVar(ILInstruction inst, [NotNullWhen(true)] ref ILVariable? containerVar)
 		{
 			if (containerVar != null)
 			{
@@ -745,7 +746,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// Matches an instruction computing a slice length:
 		///    binary.sub.i4(call GetOffset(endIndexLoad, ldloc length), ldloc startOffset))
 		/// </summary>
-		static bool MatchSliceLength(ILInstruction inst, out IndexKind endIndexKind, out ILInstruction? endIndexLoad, ILVariable containerLengthVar, ref ILVariable containerVar, ILVariable startOffsetVar)
+		static bool MatchSliceLength(ILInstruction inst, out IndexKind endIndexKind, [NotNullWhen(true)] out ILInstruction? endIndexLoad, ILVariable containerLengthVar, ref ILVariable containerVar, ILVariable startOffsetVar)
 		{
 			endIndexKind = default;
 			endIndexLoad = default;

ICSharpCode.Decompiler/IL/Transforms/InterpolatedStringTransform.cs

@@ -18,6 +18,7 @@
 
 using System;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 
 using ICSharpCode.Decompiler.TypeSystem;
 
@@ -104,7 +105,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return true;
 		}
 
-		private bool FindToStringAndClear(Block block, int pos, int interpolationStart, int interpolationEnd, ILVariable v, out ILInstruction? insertionPoint)
+		private bool FindToStringAndClear(Block block, int pos, int interpolationStart, int interpolationEnd, ILVariable v, [NotNullWhen(true)] out ILInstruction? insertionPoint)
 		{
 			insertionPoint = null;
 			if (pos >= block.Instructions.Count)

ICSharpCode.Decompiler/IL/Transforms/LocalFunctionDecompiler.cs

@@ -20,6 +20,7 @@ using System;
 using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Reflection;
 using System.Reflection.Metadata;
@@ -831,7 +832,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// </summary>
 		static readonly Regex functionNameRegex = new Regex(@"^<(.*)>g__([^\|]*)\|{0,1}\d+(_\d+)?$", RegexOptions.Compiled);
 
-		internal static bool ParseLocalFunctionName(string name, out string? callerName, out string? functionName)
+		internal static bool ParseLocalFunctionName(string name, [NotNullWhen(true)] out string? callerName, [NotNullWhen(true)] out string? functionName)
 		{
 			callerName = null;
 			functionName = null;

ICSharpCode.Decompiler/IL/Transforms/LockTransform.cs

@@ -16,6 +16,8 @@
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
 
+using System.Diagnostics.CodeAnalysis;
+
 using ICSharpCode.Decompiler.TypeSystem;
 
 namespace ICSharpCode.Decompiler.IL.Transforms
@@ -331,7 +333,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return true;
 		}
 
-		bool MatchLockEntryPoint(Block entryPoint, ILVariable flag, out StLoc? obj)
+		bool MatchLockEntryPoint(Block entryPoint, ILVariable flag, [NotNullWhen(true)] out StLoc? obj)
 		{
 			obj = null;
 			if (entryPoint.Instructions.Count == 0 || entryPoint.IncomingEdgeCount != 1)
@@ -341,14 +343,14 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return true;
 		}
 
-		bool MatchLockEntryPoint(Block entryPoint, ILVariable flag, out ILVariable? exitVairable, out StLoc? obj)
+		bool MatchLockEntryPoint(Block entryPoint, ILVariable flag, [NotNullWhen(true)] out ILVariable? exitVariable, [NotNullWhen(true)] out StLoc? obj)
 		{
 			// This pattern is commonly seen in yield return state machines emitted by the legacy C# compiler.
 			obj = null;
-			exitVairable = null;
+			exitVariable = null;
 			if (entryPoint.Instructions.Count < 1 || entryPoint.IncomingEdgeCount != 1)
 				return false;
-			if (entryPoint.Instructions[0].MatchStLoc(out exitVairable, out var value) && value is StLoc nestedStloc)
+			if (entryPoint.Instructions[0].MatchStLoc(out exitVariable, out var value) && value is StLoc nestedStloc)
 			{
 				obj = nestedStloc;
 				if (!MatchCall(entryPoint.Instructions[1] as Call, "Enter", nestedStloc.Variable, flag))
@@ -358,7 +360,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return false;
 		}
 
-		bool MatchCall(Call call, string methodName, ILVariable flag, out StLoc? obj)
+		bool MatchCall(Call? call, string methodName, ILVariable flag, [NotNullWhen(true)] out StLoc? obj)
 		{
 			obj = null;
 			const string ThreadingMonitor = "System.Threading.Monitor";
@@ -371,7 +373,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return true;
 		}
 
-		bool MatchCall(Call call, string methodName, params ILVariable[] variables)
+		bool MatchCall(Call? call, string methodName, params ILVariable[] variables)
 		{
 			const string ThreadingMonitor = "System.Threading.Monitor";
 			if (call == null || call.Method.Name != methodName || call.Method.DeclaringType.FullName != ThreadingMonitor ||

ICSharpCode.Decompiler/IL/Transforms/NullPropagationTransform.cs

@@ -18,6 +18,7 @@
 
 using System;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 
 using ICSharpCode.Decompiler.TypeSystem;
@@ -237,7 +238,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			).WithILRange(ifInst));
 		}
 
-		bool IsValidAccessChain(ILVariable testedVar, Mode mode, ILInstruction inst, out ILInstruction? finalLoad)
+		bool IsValidAccessChain(ILVariable testedVar, Mode mode, ILInstruction inst, [NotNullWhen(true)] out ILInstruction? finalLoad)
 		{
 			finalLoad = null;
 			int chainLength = 0;
@@ -475,7 +476,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 
 		// stloc resultTemporary(constrained[type].call_instruction(ldloc target, ...))
 		// br endBlock
-		private bool MatchStLocResultTemporary(Block block, int pos, IType type, ILVariable target, ILVariable defaultTemporary, ILInstruction fallbackBlock, out ILInstruction? nonNullInst, out ILInstruction? nullInst, out Block? endBlock)
+		private bool MatchStLocResultTemporary(Block block, int pos, IType type, ILVariable target, ILVariable defaultTemporary, ILInstruction fallbackBlock, [NotNullWhen(true)] out ILInstruction? nonNullInst, [NotNullWhen(true)] out ILInstruction? nullInst, [NotNullWhen(true)] out Block? endBlock)
 		{
 			endBlock = null;
 			nonNullInst = null;
@@ -496,7 +497,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return true;
 		}
 
-		private bool MatchLeaveResult(Block block, int pos, IType type, ILVariable target, ILVariable defaultTemporary, ILInstruction fallbackBlock, out ILInstruction? nonNullInst, out ILInstruction? nullInst)
+		private bool MatchLeaveResult(Block block, int pos, IType type, ILVariable target, ILVariable defaultTemporary, ILInstruction fallbackBlock, [NotNullWhen(true)] out ILInstruction? nonNullInst, [NotNullWhen(true)] out ILInstruction? nullInst)
 		{
 			nonNullInst = null;
 			nullInst = null;
@@ -508,6 +509,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			// Analyze Block fallbackBlock
 			if (!(fallbackBlock is Block b && IsFallbackBlock(b, type, target, defaultTemporary, null, leave.TargetContainer, out nullInst)))
 				return false;
+
 			return true;
 		}
 
@@ -519,7 +521,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		// 		br endBlock
 		// 	}
 		// }
-		private bool IsFallbackBlock(Block block, IType type, ILVariable target, ILVariable defaultTemporary, ILVariable resultTemporary, ILInstruction endBlockOrLeaveContainer, out ILInstruction? nullInst)
+		private bool IsFallbackBlock(Block block, IType type, ILVariable target, ILVariable defaultTemporary, ILVariable? resultTemporary, ILInstruction endBlockOrLeaveContainer, [NotNullWhen(true)] out ILInstruction? nullInst)
 		{
 			nullInst = null;
 			if (!(block.Instructions.Count == 3))

ICSharpCode.Decompiler/IL/Transforms/NullableLiftingTransform.cs

@@ -18,6 +18,7 @@
 
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 
 using ICSharpCode.Decompiler.TypeSystem;
@@ -371,7 +372,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				compRight.MatchLdNull();
 		}
 
-		private bool MatchThreeValuedLogicConditionPattern(ILInstruction condition, out ILVariable? nullable1, out ILVariable? nullable2)
+		private bool MatchThreeValuedLogicConditionPattern(ILInstruction condition, [NotNullWhen(true)] out ILVariable? nullable1, [NotNullWhen(true)] out ILVariable? nullable2)
 		{
 			// Try to match: nullable1.GetValueOrDefault() || (!nullable2.GetValueOrDefault() && !nullable1.HasValue)
 			nullable1 = null;
@@ -518,7 +519,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		#endregion
 
 		#region Lift...Comparison
-		ILInstruction LiftCSharpEqualityComparison(CompOrDecimal valueComp, ComparisonKind newComparisonKind, ILInstruction hasValueTest)
+		ILInstruction? LiftCSharpEqualityComparison(CompOrDecimal valueComp, ComparisonKind newComparisonKind, ILInstruction hasValueTest)
 		{
 			Debug.Assert(newComparisonKind.IsEqualityOrInequality());
 			bool hasValueTestNegated = false;
@@ -535,9 +536,9 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				// Comparing two nullables: HasValue comparison must be the same operator as the Value comparison
 				if ((hasValueTestNegated ? hasValueComp.Kind.Negate() : hasValueComp.Kind) != newComparisonKind)
 					return null;
-				if (!MatchHasValueCall(hasValueComp.Left, out ILVariable leftVar))
+				if (!MatchHasValueCall(hasValueComp.Left, out ILVariable? leftVar))
 					return null;
-				if (!MatchHasValueCall(hasValueComp.Right, out ILVariable rightVar))
+				if (!MatchHasValueCall(hasValueComp.Right, out ILVariable? rightVar))
 					return null;
 				nullableVars = new List<ILVariable> { leftVar };
 				var (left, leftBits) = DoLift(valueComp.Left);
@@ -551,7 +552,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					return valueComp.MakeLifted(newComparisonKind, left, right);
 				}
 			}
-			else if (newComparisonKind == ComparisonKind.Equality && !hasValueTestNegated && MatchHasValueCall(hasValueTest, out ILVariable v))
+			else if (newComparisonKind == ComparisonKind.Equality && !hasValueTestNegated && MatchHasValueCall(hasValueTest, out ILVariable? v))
 			{
 				// Comparing nullable with non-nullable -> we can fall back to the normal comparison code.
 				nullableVars = new List<ILVariable> { v };
@@ -578,7 +579,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// This means unlike LiftNormal(), we cannot rely on the input instruction not being evaluated if
 		/// a variable is <c>null</c>.
 		/// </summary>
-		ILInstruction LiftCSharpComparison(CompOrDecimal comp, ComparisonKind newComparisonKind)
+		ILInstruction? LiftCSharpComparison(CompOrDecimal comp, ComparisonKind newComparisonKind)
 		{
 			if (comp.IsLifted)
 			{
@@ -614,7 +615,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return null;
 		}
 
-		ILInstruction LiftCSharpUserEqualityComparison(CompOrDecimal hasValueComp, ComparisonKind newComparisonKind, ILInstruction nestedIfInst)
+		ILInstruction? LiftCSharpUserEqualityComparison(CompOrDecimal hasValueComp, ComparisonKind newComparisonKind, ILInstruction nestedIfInst)
 		{
 			// User-defined equality operator:
 			//   if (comp(call get_HasValue(ldloca nullable1) == call get_HasValue(ldloca nullable2)))
@@ -635,13 +636,13 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			//         ldc.i4 0
 			if (hasValueComp.IsLifted)
 				return null;
-			if (!MatchHasValueCall(hasValueComp.Left, out ILVariable nullable1))
+			if (!MatchHasValueCall(hasValueComp.Left, out ILVariable? nullable1))
 				return null;
-			if (!MatchHasValueCall(hasValueComp.Right, out ILVariable nullable2))
+			if (!MatchHasValueCall(hasValueComp.Right, out ILVariable? nullable2))
 				return null;
 			if (!nestedIfInst.MatchIfInstructionPositiveCondition(out var condition, out var trueInst, out var falseInst))
 				return null;
-			if (!MatchHasValueCall(condition, out ILVariable nullable))
+			if (!MatchHasValueCall(condition, out ILVariable? nullable))
 				return null;
 			if (nullable != nullable1 && nullable != nullable2)
 				return null;
@@ -687,7 +688,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return null;
 		}
 
-		ILInstruction LiftCSharpUserComparison(ILInstruction trueInst, ILInstruction falseInst)
+		ILInstruction? LiftCSharpUserComparison(ILInstruction trueInst, ILInstruction falseInst)
 		{
 			// (v1 != null && ... && vn != null) ? trueInst : falseInst
 			bool trueInstNegated = false;
@@ -745,13 +746,13 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// where the v1,...,vn are the <c>this.nullableVars</c>.
 		/// If lifting fails, returns <c>null</c>.
 		/// </summary>
-		ILInstruction LiftNormal(ILInstruction trueInst, ILInstruction falseInst)
+		ILInstruction? LiftNormal(ILInstruction trueInst, ILInstruction falseInst)
 		{
 			if (trueInst.MatchIfInstructionPositiveCondition(out var nestedCondition, out var nestedTrue, out var nestedFalse))
 			{
 				// Sometimes Roslyn generates pointless conditions like:
 				//   if (nullable.HasValue && (!nullable.HasValue || nullable.GetValueOrDefault() == b))
-				if (MatchHasValueCall(nestedCondition, out ILVariable v) && nullableVars.Contains(v))
+				if (MatchHasValueCall(nestedCondition, out ILVariable? v) && nullableVars.Contains(v))
 				{
 					trueInst = nestedTrue;
 				}
@@ -851,9 +852,9 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// If any relevant variable is null, the new instruction is guaranteed to evaluate to <c>null</c>
 		/// without having any other effect.
 		/// </summary>
-		(ILInstruction, BitSet) DoLift(ILInstruction inst)
+		(ILInstruction?, BitSet?) DoLift(ILInstruction inst)
 		{
-			if (MatchGetValueOrDefault(inst, out ILVariable inputVar))
+			if (MatchGetValueOrDefault(inst, out ILVariable? inputVar))
 			{
 				// n.GetValueOrDefault() lifted => n.
 				BitSet foundIndices = new BitSet(nullableVars.Count);
@@ -916,7 +917,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				}
 			}
 			else if (inst is Comp comp && !comp.IsLifted && comp.Kind == ComparisonKind.Equality
-			  && MatchGetValueOrDefault(comp.Left, out ILVariable v) && nullableVars.Contains(v)
+			  && MatchGetValueOrDefault(comp.Left, out ILVariable? v) && nullableVars.Contains(v)
 			  && NullableType.GetUnderlyingType(v.Type).IsKnownType(KnownTypeCode.Boolean)
 			  && comp.Right.MatchLdcI4(0)
 		  )
@@ -934,8 +935,8 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				var liftedOperator = CSharp.Resolver.CSharpOperators.LiftUserDefinedOperator(call.Method);
 				if (liftedOperator == null || !NullableType.IsNullable(liftedOperator.ReturnType))
 					return (null, null);
-				ILInstruction[] newArgs;
-				BitSet newBits;
+				ILInstruction?[] newArgs;
+				BitSet? newBits;
 				if (call.Arguments.Count == 1)
 				{
 					var (arg, bits) = DoLift(call.Arguments[0]);
@@ -969,7 +970,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return (null, null);
 		}
 
-		(ILInstruction, ILInstruction, BitSet) DoLiftBinary(ILInstruction lhs, ILInstruction rhs, IType leftExpectedType, IType rightExpectedType)
+		(ILInstruction?, ILInstruction?, BitSet?) DoLiftBinary(ILInstruction lhs, ILInstruction rhs, IType leftExpectedType, IType rightExpectedType)
 		{
 			var (left, leftBits) = DoLift(lhs);
 			var (right, rightBits) = DoLift(rhs);
@@ -1018,7 +1019,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// <summary>
 		/// Matches 'call get_HasValue(arg)'
 		/// </summary>
-		internal static bool MatchHasValueCall(ILInstruction inst, out ILInstruction? arg)
+		internal static bool MatchHasValueCall(ILInstruction inst, [NotNullWhen(true)] out ILInstruction? arg)
 		{
 			arg = null;
 			if (!(inst is Call call))
@@ -1036,9 +1037,9 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// <summary>
 		/// Matches 'call get_HasValue(ldloca v)'
 		/// </summary>
-		internal static bool MatchHasValueCall(ILInstruction inst, out ILVariable? v)
+		internal static bool MatchHasValueCall(ILInstruction inst, [NotNullWhen(true)] out ILVariable? v)
 		{
-			if (MatchHasValueCall(inst, out ILInstruction arg))
+			if (MatchHasValueCall(inst, out ILInstruction? arg))
 			{
 				return arg.MatchLdLoca(out v);
 			}
@@ -1051,7 +1052,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// </summary>
 		internal static bool MatchHasValueCall(ILInstruction inst, ILVariable v)
 		{
-			return MatchHasValueCall(inst, out ILVariable v2) && v == v2;
+			return MatchHasValueCall(inst, out ILVariable? v2) && v == v2;
 		}
 
 		/// <summary>
@@ -1065,7 +1066,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// <summary>
 		/// Matches 'newobj Nullable{underlyingType}.ctor(arg)'
 		/// </summary>
-		internal static bool MatchNullableCtor(ILInstruction inst, out IType? underlyingType, out ILInstruction? arg)
+		internal static bool MatchNullableCtor(ILInstruction inst, [NotNullWhen(true)] out IType? underlyingType, [NotNullWhen(true)] out ILInstruction? arg)
 		{
 			underlyingType = null;
 			arg = null;
@@ -1083,7 +1084,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// <summary>
 		/// Matches 'call Nullable{T}.GetValueOrDefault(arg)'
 		/// </summary>
-		internal static bool MatchGetValueOrDefault(ILInstruction inst, out ILInstruction? arg)
+		internal static bool MatchGetValueOrDefault(ILInstruction inst, [NotNullWhen(true)] out ILInstruction? arg)
 		{
 			arg = null;
 			if (!(inst is Call call))
@@ -1099,7 +1100,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// <summary>
 		/// Matches 'call nullableValue.GetValueOrDefault(fallback)'
 		/// </summary>
-		internal static bool MatchGetValueOrDefault(ILInstruction inst, out ILInstruction? nullableValue, out ILInstruction? fallback)
+		internal static bool MatchGetValueOrDefault(ILInstruction inst, [NotNullWhen(true)] out ILInstruction? nullableValue, [NotNullWhen(true)] out ILInstruction? fallback)
 		{
 			nullableValue = null;
 			fallback = null;
@@ -1117,10 +1118,10 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// <summary>
 		/// Matches 'call Nullable{T}.GetValueOrDefault(ldloca v)'
 		/// </summary>
-		internal static bool MatchGetValueOrDefault(ILInstruction inst, out ILVariable? v)
+		internal static bool MatchGetValueOrDefault(ILInstruction inst, [NotNullWhen(true)] out ILVariable? v)
 		{
 			v = null;
-			return MatchGetValueOrDefault(inst, out ILInstruction arg)
+			return MatchGetValueOrDefault(inst, out ILInstruction? arg)
 				&& arg.MatchLdLoca(out v);
 		}
 
@@ -1129,13 +1130,13 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// </summary>
 		internal static bool MatchGetValueOrDefault(ILInstruction inst, ILVariable v)
 		{
-			return MatchGetValueOrDefault(inst, out ILVariable v2) && v == v2;
+			return MatchGetValueOrDefault(inst, out ILVariable? v2) && v == v2;
 		}
 
-		static bool MatchNull(ILInstruction inst, out IType? underlyingType)
+		static bool MatchNull(ILInstruction inst, [NotNullWhen(true)] out IType? underlyingType)
 		{
 			underlyingType = null;
-			if (inst.MatchDefaultValue(out IType type))
+			if (inst.MatchDefaultValue(out var type))
 			{
 				underlyingType = NullableType.GetUnderlyingType(type);
 				return NullableType.IsNullable(type);

ICSharpCode.Decompiler/IL/Transforms/SwitchOnNullableTransform.cs

@@ -18,6 +18,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 
 using ICSharpCode.Decompiler.IL.ControlFlow;
@@ -77,7 +78,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// <summary>
 		/// Matches legacy C# switch on nullable.
 		/// </summary>
-		bool MatchSwitchOnNullable(InstructionCollection<ILInstruction> instructions, int i, out SwitchInstruction? newSwitch)
+		bool MatchSwitchOnNullable(InstructionCollection<ILInstruction> instructions, int i, [NotNullWhen(true)] out SwitchInstruction? newSwitch)
 		{
 			newSwitch = null;
 			// match first block:
@@ -133,7 +134,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// <summary>
 		/// Matches Roslyn C# switch on nullable.
 		/// </summary>
-		bool MatchRoslynSwitchOnNullable(InstructionCollection<ILInstruction> instructions, int i, out SwitchInstruction? newSwitch)
+		bool MatchRoslynSwitchOnNullable(InstructionCollection<ILInstruction> instructions, int i, [NotNullWhen(true)] out SwitchInstruction? newSwitch)
 		{
 			newSwitch = null;
 			// match first block:
@@ -143,7 +144,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				return false;
 			if (!instructions[i + 1].MatchBranch(out var switchBlock) || !trueInst.MatchBranch(out var nullCaseBlock))
 				return false;
-			if (!condition.MatchLogicNot(out var getHasValue) || !NullableLiftingTransform.MatchHasValueCall(getHasValue, out ILInstruction target) || !SemanticHelper.IsPure(target.Flags))
+			if (!condition.MatchLogicNot(out var getHasValue) || !NullableLiftingTransform.MatchHasValueCall(getHasValue, out ILInstruction? target) || !SemanticHelper.IsPure(target.Flags))
 				return false;
 			// match second block: switchBlock
 			// note: I have seen cases where switchVar is inlined into the switch.
@@ -165,7 +166,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 						return false;
 					if (!switchVar.IsSingleDefinition || switchVar.LoadCount != 1)
 						return false;
-					if (!(NullableLiftingTransform.MatchGetValueOrDefault(getValueOrDefault, out ILInstruction target2) && target2.Match(target).Success))
+					if (!(NullableLiftingTransform.MatchGetValueOrDefault(getValueOrDefault, out ILInstruction? target2) && target2.Match(target).Success))
 						return false;
 					if (!(switchBlock.Instructions[1] is SwitchInstruction si))
 						return false;

ICSharpCode.Decompiler/IL/Transforms/SwitchOnStringTransform.cs

@@ -18,6 +18,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 
 using ICSharpCode.Decompiler.IL.ControlFlow;
@@ -473,7 +474,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return true;
 		}
 
-		bool IsIsInternedCall(Call call, out ILInstruction? argument)
+		bool IsIsInternedCall(Call call, [NotNullWhen(true)] out ILInstruction? argument)
 		{
 			if (call != null
 				&& call.Method.DeclaringType.IsKnownType(KnownTypeCode.String)
@@ -503,7 +504,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// The <paramref name="switchVariable"/> is updated if the value gets copied to a different variable.
 		/// See comments below for more info.
 		/// </summary>
-		ILInstruction MatchCaseBlock(Block currentBlock, ILVariable switchVariable, out string? value, out bool emptyStringEqualsNull, out ILInstruction? caseBlockOrLeave)
+		ILInstruction? MatchCaseBlock(Block currentBlock, ILVariable switchVariable, out string? value, out bool emptyStringEqualsNull, out ILInstruction? caseBlockOrLeave)
 		{
 			value = null;
 			caseBlockOrLeave = null;
@@ -534,12 +535,12 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			{
 				return null;
 			}
-			if (nextBlockBranch.MatchBranch(out Block nextBlock))
+			if (nextBlockBranch.MatchBranch(out Block? nextBlock))
 			{
 				// success
 				return nextBlock;
 			}
-			else if (nextBlockBranch.MatchLeave(out BlockContainer blockContainer))
+			else if (nextBlockBranch.MatchLeave(out BlockContainer? blockContainer))
 			{
 				// success
 				return blockContainer;
@@ -740,7 +741,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return true;
 		}
 
-		bool AddNullSection(List<SwitchSection> sections, List<(string Value, int Index)> stringValues, Block nullValueCaseBlock)
+		bool AddNullSection(List<SwitchSection> sections, List<(string? Value, int Index)> stringValues, Block nullValueCaseBlock)
 		{
 			var label = new LongSet(stringValues.Max(item => item.Index) + 1);
 			var possibleConflicts = sections.Where(sec => sec.Labels.Overlaps(label)).ToArray();
@@ -760,7 +761,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// <summary>
 		/// Matches 'volatile.ldobj dictionaryType(ldsflda dictField)'
 		/// </summary>
-		bool MatchDictionaryFieldLoad(ILInstruction inst, Func<IType, bool> typeMatcher, out IField? dictField, out IType? dictionaryType)
+		bool MatchDictionaryFieldLoad(ILInstruction inst, Func<IType, bool> typeMatcher, [NotNullWhen(true)] out IField? dictField, [NotNullWhen(true)] out IType? dictionaryType)
 		{
 			dictField = null;
 			dictionaryType = null;
@@ -773,7 +774,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// <summary>
 		/// Matches and extracts values from Add-call sequences.
 		/// </summary>
-		bool ExtractStringValuesFromInitBlock(Block block, out List<(string, int)>? values, out Block? blockAfterInit, IType dictionaryType, IField dictionaryField, bool isHashtablePattern)
+		bool ExtractStringValuesFromInitBlock(Block block, [NotNullWhen(true)] out List<(string?, int)>? values, [NotNullWhen(true)] out Block? blockAfterInit, IType dictionaryType, IField dictionaryField, bool isHashtablePattern)
 		{
 			values = null;
 			blockAfterInit = null;
@@ -797,7 +798,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				if (!newObj.Arguments[0].MatchLdcI4(out valuesLength))
 					return false;
 			}
-			values = new List<(string, int)>(valuesLength);
+			values = new List<(string?, int)>(valuesLength);
 			int i = 0;
 			while (MatchAddCall(dictionaryType, block.Instructions[i + 1], dictVar, out var index, out var value))
 			{
@@ -822,7 +823,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// -or-
 		/// call Add(ldloc dictVar, ldstr value, box System.Int32(ldc.i4 index))
 		/// </summary>
-		bool MatchAddCall(IType dictionaryType, ILInstruction inst, ILVariable dictVar, out int index, out string? value)
+		bool MatchAddCall(IType dictionaryType, ILInstruction inst, ILVariable dictVar, out int index, [NotNullWhen(true)] out string? value)
 		{
 			value = null;
 			index = -1;
@@ -941,7 +942,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return true;
 		}
 
-		bool FindHashtableInitBlock(Block entryPoint, out List<(string, int)>? stringValues, out IField? dictField, out Block? blockAfterThisInitBlock, out ILInstruction? thisSwitchInitJumpInst, out ILInstruction? nextSwitchInitJumpInst)
+		bool FindHashtableInitBlock(Block entryPoint, out List<(string?, int)>? stringValues, out IField? dictField, out Block? blockAfterThisInitBlock, out ILInstruction? thisSwitchInitJumpInst, out ILInstruction? nextSwitchInitJumpInst)
 		{
 			stringValues = null;
 			dictField = null;
@@ -1310,7 +1311,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				}
 			}
 
-			bool MatchSwitchOnCharBlock(Block block, int length, ILVariable switchValueVar, out List<(string StringValue, ILInstruction BodyOrLeave)>? results)
+			bool MatchSwitchOnCharBlock(Block block, int length, ILVariable switchValueVar, [NotNullWhen(true)] out List<(string StringValue, ILInstruction BodyOrLeave)>? results)
 			{
 				results = null;
 				if (block.IncomingEdgeCount != 1)
@@ -1399,12 +1400,12 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				return results?.Count > 0;
 			}
 
-			bool MatchSwitchOnLengthBlock(ref ILVariable switchValueVar, Block switchOnLengthBlock, int startOffset, out List<(LongSet Length, Block TargetBlock)>? blocks)
+			bool MatchSwitchOnLengthBlock(ref ILVariable switchValueVar, Block switchOnLengthBlock, int startOffset, [NotNullWhen(true)] out List<(LongSet Length, Block TargetBlock)>? blocks)
 			{
 				blocks = null;
 				SwitchInstruction? @switch;
-				ILInstruction getLengthCall;
-				ILVariable lengthVar;
+				ILInstruction? getLengthCall;
+				ILVariable? lengthVar;
 				switch (switchOnLengthBlock.Instructions.Count - startOffset)
 				{
 					case 1:
@@ -1506,7 +1507,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		///	    br newDefaultBlock
 		/// }
 		/// </summary>
-		private bool IsNullCheckInDefaultBlock(ref Block exitOrDefaultBlock, ILVariable switchVar, out Block? nullValueCaseBlock)
+		private bool IsNullCheckInDefaultBlock(ref Block exitOrDefaultBlock, ILVariable switchVar, [NotNullWhen(true)] out Block? nullValueCaseBlock)
 		{
 			nullValueCaseBlock = null;
 			if (exitOrDefaultBlock == null)
@@ -1532,7 +1533,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// if (call op_Equality(ldloc switchValueVar, stringValue)) br body
 		/// br exit
 		/// </summary>
-		bool MatchRoslynCaseBlockHead(Block target, ILVariable switchValueVar, out ILInstruction? bodyOrLeave, out Block? defaultOrExitBlock, out string? stringValue, out bool emptyStringEqualsNull)
+		bool MatchRoslynCaseBlockHead(Block target, ILVariable switchValueVar, [NotNullWhen(true)] out ILInstruction? bodyOrLeave, [NotNullWhen(true)] out Block? defaultOrExitBlock, [NotNullWhen(true)] out string? stringValue, out bool emptyStringEqualsNull)
 		{
 			bodyOrLeave = null;
 			defaultOrExitBlock = null;
@@ -1592,7 +1593,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// 	br exit
 		/// }
 		/// </summary>
-		bool MatchRoslynEmptyStringCaseBlockHead(Block target, ILVariable switchValueVar, out ILInstruction? bodyOrLeave, out Block? defaultOrExitBlock)
+		bool MatchRoslynEmptyStringCaseBlockHead(Block target, ILVariable switchValueVar, [NotNullWhen(true)] out ILInstruction? bodyOrLeave, [NotNullWhen(true)] out Block? defaultOrExitBlock)
 		{
 			bodyOrLeave = null;
 			defaultOrExitBlock = null;
@@ -1602,7 +1603,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				return false;
 			if (!nullComparisonCondition.MatchCompEqualsNull(out var arg) || !arg.MatchLdLoc(switchValueVar))
 				return false;
-			if (!target.Instructions[1].MatchBranch(out Block lengthCheckBlock))
+			if (!target.Instructions[1].MatchBranch(out Block? lengthCheckBlock))
 				return false;
 			if (lengthCheckBlock.Instructions.Count != 2 || lengthCheckBlock.IncomingEdgeCount != 1)
 				return false;
@@ -1660,7 +1661,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// - or -
 		/// 'stloc(targetVar, call ComputeReadOnlySpanHash(ldloc switchValue))'
 		/// </summary>
-		internal static bool MatchComputeStringOrReadOnlySpanHashCall(ILInstruction inst, ILVariable targetVar, out LdLoc? switchValue)
+		internal static bool MatchComputeStringOrReadOnlySpanHashCall(ILInstruction inst, ILVariable targetVar, [NotNullWhen(true)] out LdLoc? switchValue)
 		{
 			switchValue = null;
 			if (!inst.MatchStLoc(targetVar, out var value))
@@ -1682,7 +1683,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		///      or 'comp(ldloc(variable) == ldnull)'
 		///      or 'call SequenceEqual(ldloc variable, call AsSpan(ldstr stringValue))'
 		/// </summary>
-		bool MatchStringEqualityComparison(ILInstruction condition, ILVariable variable, out string stringValue, out bool isVBCompareString)
+		bool MatchStringEqualityComparison(ILInstruction condition, ILVariable variable, out string? stringValue, out bool isVBCompareString)
 		{
 			return MatchStringEqualityComparison(condition, out var v, out stringValue, out isVBCompareString) && v == variable;
 		}
@@ -1692,7 +1693,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		///      or 'comp(ldloc(variable) == ldnull)'
 		///      or 'call SequenceEqual(ldloc variable, call AsSpan(ldstr stringValue))'
 		/// </summary>
-		bool MatchStringEqualityComparison(ILInstruction condition, out ILVariable? variable, out string? stringValue, out bool isVBCompareString)
+		bool MatchStringEqualityComparison(ILInstruction condition, [NotNullWhen(true)] out ILVariable? variable, out string? stringValue, out bool isVBCompareString)
 		{
 			stringValue = null;
 			variable = null;

ICSharpCode.Decompiler/IL/Transforms/TransformArrayInitializers.cs

@@ -18,6 +18,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Reflection.Metadata;
 using System.Text;
@@ -114,7 +115,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return false;
 		}
 
-		internal static bool TransformSpanTArrayInitialization(NewObj inst, StatementTransformContext context, out ILInstruction? replacement)
+		internal static bool TransformSpanTArrayInitialization(NewObj inst, StatementTransformContext context, [NotNullWhen(true)] out ILInstruction? replacement)
 		{
 			replacement = null;
 			if (!context.Settings.ArrayInitializers)
@@ -143,7 +144,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return false;
 		}
 
-		private static unsafe bool DecodeUTF8String(BlobReader blob, int size, out string? text)
+		private static unsafe bool DecodeUTF8String(BlobReader blob, int size, [NotNullWhen(true)] out string? text)
 		{
 			if (size > blob.RemainingBytes)
 			{
@@ -166,7 +167,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return MemoryExtensions.SequenceEqual(bytes, new ReadOnlySpan<byte>(blob.CurrentPointer, size));
 		}
 
-		static bool MatchSpanTCtorWithPointerAndSize(NewObj newObj, StatementTransformContext context, out IType? elementType, out FieldDefinition field, out int size)
+		static bool MatchSpanTCtorWithPointerAndSize(NewObj newObj, StatementTransformContext context, [NotNullWhen(true)] out IType? elementType, [NotNullWhen(true)] out FieldDefinition field, out int size)
 		{
 			field = default;
 			size = default;
@@ -288,7 +289,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			}
 		}
 
-		bool HandleCpblkInitializer(Block block, int pos, ILVariable v, long length, out BlobReader blob, out IType? elementType)
+		bool HandleCpblkInitializer(Block block, int pos, ILVariable v, long length, [NotNullWhen(true)] out BlobReader blob, [NotNullWhen(true)] out IType? elementType)
 		{
 			blob = default;
 			elementType = null;
@@ -334,7 +335,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return true;
 		}
 
-		bool MatchGetStaticFieldAddress(ILInstruction input, out IField field)
+		bool MatchGetStaticFieldAddress(ILInstruction input, [NotNullWhen(true)] out IField? field)
 		{
 			if (input.MatchLdsFlda(out field))
 				return true;
@@ -359,7 +360,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 
 		static bool IsRuntimeHelpers(IType type) => type is { Name: "RuntimeHelpers", Namespace: "System.Runtime.CompilerServices" };
 
-		unsafe bool HandleSequentialLocAllocInitializer(Block block, int pos, ILVariable store, ILInstruction locAllocInstruction, out IType? elementType, out StObj[]? values, out int instructionsToRemove)
+		unsafe bool HandleSequentialLocAllocInitializer(Block block, int pos, ILVariable store, ILInstruction locAllocInstruction, [NotNullWhen(true)] out IType? elementType, [NotNullWhen(true)] out StObj[]? values, out int instructionsToRemove)
 		{
 			int elementCount = 0;
 			long minExpectedOffset = 0;
@@ -399,7 +400,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			for (int i = pos; i < block.Instructions.Count; i++)
 			{
 				// match the basic stobj pattern
-				if (!block.Instructions[i].MatchStObj(out ILInstruction target, out var value, out var currentType)
+				if (!block.Instructions[i].MatchStObj(out ILInstruction? target, out var value, out var currentType)
 					|| value.Descendants.OfType<IInstructionWithVariableOperand>().Any(inst => inst.Variable == store))
 					break;
 				// first
@@ -462,7 +463,6 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				elementType = ((PointerType)finalStore.Variable.Type).ElementType;
 			}
 			instructionsToRemove += elementCount;
-
 			return elementCount <= values.Length;
 		}
 
@@ -498,7 +498,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// <summary>
 		/// Handle simple case where RuntimeHelpers.InitializeArray is not used.
 		/// </summary>
-		internal static bool HandleSimpleArrayInitializer(ILFunction function, Block block, int pos, ILVariable store, int[] arrayLength, out (ILInstruction[] Indices, ILInstruction Value)[]? values, out int instructionsToRemove)
+		internal static bool HandleSimpleArrayInitializer(ILFunction function, Block block, int pos, ILVariable store, int[] arrayLength, [NotNullWhen(true)] out (ILInstruction[] Indices, ILInstruction? Value)[]? values, out int instructionsToRemove)
 		{
 			instructionsToRemove = 0;
 			int elementCount = 0;
@@ -508,11 +508,11 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			// To prevent excessive allocations, use min(|block|, arraySize) als initial capacity.
 			// This should prevent list-resizing as well as out-of-memory errors.
 			values = null;
-			var valuesList = new List<(ILInstruction[] Indices, ILInstruction Value)>(Math.Min(block.Instructions.Count, length));
+			var valuesList = new List<(ILInstruction[] Indices, ILInstruction? Value)>(Math.Min(block.Instructions.Count, length));
 
 			int[] nextMinimumIndex = new int[arrayLength.Length];
 
-			ILInstruction[] CalculateNextIndices(InstructionCollection<ILInstruction> indices, out bool exactMatch)
+			ILInstruction[]? CalculateNextIndices(InstructionCollection<ILInstruction>? indices, out bool exactMatch)
 			{
 				var nextIndices = new ILInstruction[arrayLength.Length];
 				exactMatch = true;
@@ -565,7 +565,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			{
 				InstructionCollection<ILInstruction> indices;
 				// stobj elementType(ldelema elementType(ldloc store, indices), value)
-				if (block.Instructions[i].MatchStObj(out ILInstruction target, out ILInstruction value, out IType type))
+				if (block.Instructions[i].MatchStObj(out var target, out var value, out var type))
 				{
 					if (!(target is LdElema ldelem && ldelem.Array.MatchLdLoc(store)))
 						break;
@@ -620,7 +620,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			}
 			if (i < block.Instructions.Count)
 			{
-				if (block.Instructions[i].MatchStObj(out ILInstruction target, out ILInstruction value, out IType type))
+				if (block.Instructions[i].MatchStObj(out var target, out var value, out var type))
 				{
 					// An element of the array is modified directly after the initializer:
 					// Abort transform, so that partial initializers are not constructed. 
@@ -671,7 +671,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			{
 				// 1. Instruction: (optional) temporary copy of store
 				bool hasTemporaryCopy = block.Instructions[pos].MatchStLoc(out var temp, out var storeLoad) && storeLoad.MatchLdLoc(store);
-				ILInstruction initializer;
+				ILInstruction? initializer;
 				if (hasTemporaryCopy)
 				{
 					if (!MatchJaggedArrayStore(block, pos + 1, temp, i, out initializer, out _))
@@ -703,7 +703,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return true;
 		}
 
-		bool MatchJaggedArrayStore(Block block, int pos, ILVariable store, int index, out ILInstruction? initializer, out IType? type)
+		bool MatchJaggedArrayStore(Block block, int pos, ILVariable store, int index, [NotNullWhen(true)] out ILInstruction? initializer, [NotNullWhen(true)] out IType? type)
 		{
 			initializer = null;
 			type = null;
@@ -751,7 +751,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return block;
 		}
 
-		static bool MatchNewArr(ILInstruction instruction, out IType? arrayType, out int[]? length)
+		static bool MatchNewArr(ILInstruction instruction, [NotNullWhen(true)] out IType? arrayType, [NotNullWhen(true)] out int[]? length)
 		{
 			length = null;
 			arrayType = null;
@@ -769,7 +769,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return true;
 		}
 
-		bool MatchInitializeArrayCall(ILInstruction instruction, out ILInstruction? array, out FieldDefinition field)
+		bool MatchInitializeArrayCall(ILInstruction instruction, [NotNullWhen(true)] out ILInstruction? array, [NotNullWhen(true)] out FieldDefinition field)
 		{
 			array = null;
 			field = default;
@@ -789,7 +789,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return true;
 		}
 
-		bool HandleRuntimeHelpersInitializeArray(Block body, int pos, ILVariable array, IType arrayType, int[] arrayLength, out ILInstruction[]? values, out int foundPos)
+		bool HandleRuntimeHelpersInitializeArray(Block body, int pos, ILVariable array, IType arrayType, int[] arrayLength, [NotNullWhen(true)] out ILInstruction[]? values, out int foundPos)
 		{
 			if (MatchInitializeArrayCall(body.Instructions[pos], out var arrayInst, out var field) && arrayInst.MatchLdLoc(array))
 			{

ICSharpCode.Decompiler/IL/Transforms/TransformAssignment.cs

@@ -18,6 +18,7 @@
 
 using System;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Linq.Expressions;
 
@@ -677,8 +678,8 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// 
 		/// Every IsCompoundStore() call should be followed by an IsMatchingCompoundLoad() call.
 		/// </remarks>
-		static bool IsCompoundStore(ILInstruction inst, out IType? storeType,
-			out ILInstruction? value, ICompilation compilation)
+		static bool IsCompoundStore(ILInstruction inst, [NotNullWhen(true)] out IType? storeType,
+			[NotNullWhen(true)] out ILInstruction? value, ICompilation compilation)
 		{
 			value = null;
 			storeType = null;
@@ -1025,7 +1026,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return true;
 		}
 
-		static bool IsSameMember(IMember a, IMember b)
+		static bool IsSameMember(IMember? a, IMember? b)
 		{
 			if (a == null || b == null)
 				return false;

ICSharpCode.Decompiler/IL/Transforms/TransformDisplayClassUsage.cs

@@ -19,6 +19,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Reflection.Metadata;
 
@@ -588,7 +589,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			}
 		}
 
-		internal static bool IsClosure(ILTransformContext context, ILVariable variable, out ITypeDefinition? closureType, out ILInstruction? initializer)
+		internal static bool IsClosure(ILTransformContext context, ILVariable variable, [NotNullWhen(true)] out ITypeDefinition? closureType, [NotNullWhen(true)] out ILInstruction? initializer)
 		{
 			closureType = null;
 			initializer = null;
@@ -610,7 +611,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return false;
 		}
 
-		static bool IsClosureInit(ILTransformContext context, StLoc inst, out ITypeDefinition? closureType)
+		static bool IsClosureInit(ILTransformContext context, StLoc inst, [NotNullWhen(true)] out ITypeDefinition? closureType)
 		{
 			if (inst.Value is NewObj newObj)
 			{
@@ -840,18 +841,18 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			EarlyExpressionTransforms.LdObjToLdLoc(inst, context);
 		}
 
-		private bool IsDisplayClassLoad(ILInstruction target, out ILVariable variable)
+		private bool IsDisplayClassLoad(ILInstruction target, [NotNullWhen(true)] out ILVariable? variable)
 		{
 			// We cannot use MatchLdLocRef here because local functions use ref parameters
 			if (!target.MatchLdLoc(out variable) && !target.MatchLdLoca(out variable))
 				return false;
-			if (displayClassCopyMap.TryGetValue(variable, out ILVariable other))
+			if (displayClassCopyMap.TryGetValue(variable, out ILVariable? other))
 				variable = other;
 			return true;
 		}
 
 		private bool IsDisplayClassFieldAccess(ILInstruction inst,
-			out ILVariable? displayClassVar, out DisplayClass? displayClass, out IField? field)
+			[NotNullWhen(true)] out ILVariable? displayClassVar, [NotNullWhen(true)] out DisplayClass? displayClass, [NotNullWhen(true)] out IField? field)
 		{
 			displayClass = null;
 			displayClassVar = null;
@@ -867,7 +868,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		{
 			base.VisitLdFlda(inst);
 			// Get display class info
-			if (!IsDisplayClassFieldAccess(inst, out _, out DisplayClass displayClass, out IField field))
+			if (!IsDisplayClassFieldAccess(inst, out _, out DisplayClass? displayClass, out IField? field))
 				return;
 			var keyField = (IField)field.MemberDefinition;
 			var v = displayClass.VariablesToDeclare[keyField];

ICSharpCode.Decompiler/IL/Transforms/TransformExpressionTrees.cs

@@ -19,6 +19,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 
 using ICSharpCode.Decompiler.CSharp.Resolver;
@@ -63,7 +64,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return false;
 		}
 
-		bool MatchParameterVariableAssignment(ILInstruction expr, out ILVariable parameterReferenceVar, out IType? type, out string? name)
+		bool MatchParameterVariableAssignment(ILInstruction expr, [NotNullWhen(true)] out ILVariable? parameterReferenceVar, [NotNullWhen(true)] out IType? type, [NotNullWhen(true)] out string? name)
 		{
 			// stloc(v, call(Expression::Parameter, call(Type::GetTypeFromHandle, ldtoken(...)), ldstr(...)))
 			type = null;
@@ -1124,7 +1125,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return (BuildInitializer, arrayType);
 		}
 
-		bool MatchNew(CallInstruction invocation, out IMethod? ctor)
+		bool MatchNew(CallInstruction invocation, [NotNullWhen(true)] out IMethod? ctor)
 		{
 			ctor = null;
 			if (invocation.Method.Name != "New")
@@ -1413,7 +1414,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return variable.Type.FullName == "System.Linq.Expressions.ParameterExpression";
 		}
 
-		bool MatchConstantCall(ILInstruction inst, out ILInstruction? value, out IType? type)
+		bool MatchConstantCall(ILInstruction inst, [NotNullWhen(true)] out ILInstruction? value, [NotNullWhen(true)] out IType? type)
 		{
 			value = null;
 			type = null;
@@ -1436,7 +1437,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return false;
 		}
 
-		internal static bool MatchGetTypeFromHandle(ILInstruction inst, out IType? type)
+		internal static bool MatchGetTypeFromHandle(ILInstruction inst, [NotNullWhen(true)] out IType? type)
 		{
 			type = null;
 			return inst is CallInstruction getTypeCall
@@ -1445,7 +1446,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				&& getTypeCall.Arguments[0].MatchLdTypeToken(out type);
 		}
 
-		bool MatchGetMethodFromHandle(ILInstruction inst, out IMember? member)
+		bool MatchGetMethodFromHandle(ILInstruction inst, [NotNullWhen(true)] out IMember? member)
 		{
 			member = null;
 			//castclass System.Reflection.MethodInfo(call GetMethodFromHandle(ldmembertoken op_Addition))
@@ -1458,7 +1459,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return MatchFromHandleParameterList(call, out member);
 		}
 
-		bool MatchGetConstructorFromHandle(ILInstruction inst, out IMember? member)
+		bool MatchGetConstructorFromHandle(ILInstruction inst, [NotNullWhen(true)] out IMember? member)
 		{
 			member = null;
 			//castclass System.Reflection.ConstructorInfo(call GetMethodFromHandle(ldmembertoken op_Addition))
@@ -1471,7 +1472,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return MatchFromHandleParameterList(call, out member);
 		}
 
-		bool MatchGetFieldFromHandle(ILInstruction inst, out IMember? member)
+		bool MatchGetFieldFromHandle(ILInstruction inst, [NotNullWhen(true)] out IMember? member)
 		{
 			member = null;
 			if (!(inst is CallInstruction call && call.Method.FullName == "System.Reflection.FieldInfo.GetFieldFromHandle"))
@@ -1479,7 +1480,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return MatchFromHandleParameterList(call, out member);
 		}
 
-		static bool MatchFromHandleParameterList(CallInstruction call, out IMember? member)
+		static bool MatchFromHandleParameterList(CallInstruction call, [NotNullWhen(true)] out IMember? member)
 		{
 			member = null;
 			switch (call.Arguments.Count)
@@ -1500,7 +1501,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return true;
 		}
 
-		bool MatchArgumentList(ILInstruction inst, out IList<ILInstruction>? arguments)
+		bool MatchArgumentList(ILInstruction inst, [NotNullWhen(true)] out IList<ILInstruction>? arguments)
 		{
 			arguments = null;
 			if (!(inst is Block block && block.Kind == BlockKind.ArrayInitializer))

ICSharpCode.Decompiler/IL/Transforms/TupleTransform.cs

@@ -19,6 +19,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Text;
 
 using ICSharpCode.Decompiler.TypeSystem;
@@ -59,7 +60,7 @@ namespace ICSharpCode.Decompiler.IL
 		/// Matches 'newobj TupleType(...)'.
 		/// Takes care of flattening long tuples.
 		/// </summary>
-		public static bool MatchTupleConstruction(NewObj? newobj, out ILInstruction[]? arguments)
+		public static bool MatchTupleConstruction(NewObj? newobj, [NotNullWhen(true)] out ILInstruction[]? arguments)
 		{
 			arguments = null;
 			if (newobj == null)

ICSharpCode.Decompiler/IL/Transforms/UserDefinedLogicTransform.cs

@@ -19,6 +19,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Text;
 
@@ -116,7 +117,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return false;
 		}
 
-		static bool MatchCondition(ILInstruction condition, out ILVariable? v, out string? name)
+		static bool MatchCondition(ILInstruction condition, [NotNullWhen(true)] out ILVariable? v, [NotNullWhen(true)] out string? name)
 		{
 			v = null;
 			name = null;

ICSharpCode.Decompiler/IL/Transforms/UsingTransform.cs

@@ -16,6 +16,7 @@
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
 
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 
 using ICSharpCode.Decompiler.TypeSystem;
@@ -488,7 +489,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return true;
 		}
 
-		bool CheckAsyncResourceType(IType type, out string? disposeMethodFullName)
+		bool CheckAsyncResourceType(IType type, [NotNullWhen(true)] out string? disposeMethodFullName)
 		{
 			disposeMethodFullName = null;
 			IType t = NullableType.GetUnderlyingType(type);

ICSharpCode.Decompiler/Metadata/MetadataExtensions.cs

@@ -19,6 +19,7 @@
 using System;
 using System.Buffers.Binary;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.IO;
 using System.Linq;
 using System.Reflection;
@@ -73,7 +74,7 @@ namespace ICSharpCode.Decompiler.Metadata
 				$"PublicKeyToken={publicKey}";
 		}
 
-		public static bool TryGetFullAssemblyName(this MetadataReader reader, out string? assemblyName)
+		public static bool TryGetFullAssemblyName(this MetadataReader reader, [NotNullWhen(true)] out string? assemblyName)
 		{
 			try
 			{
@@ -124,7 +125,7 @@ namespace ICSharpCode.Decompiler.Metadata
 			return builder.ToString();
 		}
 
-		public static bool TryGetFullAssemblyName(this SRM.AssemblyReference reference, MetadataReader reader, out string? assemblyName)
+		public static bool TryGetFullAssemblyName(this SRM.AssemblyReference reference, MetadataReader reader, [NotNullWhen(true)] out string? assemblyName)
 		{
 			try
 			{

ICSharpCode.Decompiler/Metadata/ReferenceLoadInfo.cs

@@ -18,6 +18,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 
 namespace ICSharpCode.Decompiler.Metadata
@@ -58,7 +59,7 @@ namespace ICSharpCode.Decompiler.Metadata
 			}
 		}
 
-		public bool TryGetInfo(string fullName, out UnresolvedAssemblyNameReference info)
+		public bool TryGetInfo(string fullName, [NotNullWhen(true)] out UnresolvedAssemblyNameReference? info)
 		{
 			lock (loadedAssemblyReferences)
 			{

ICSharpCode.Decompiler/TypeSystem/GenericContext.cs

@@ -34,7 +34,7 @@ namespace ICSharpCode.Decompiler.TypeSystem
 			this.MethodTypeParameters = null;
 		}
 
-		public GenericContext(IReadOnlyList<ITypeParameter> classTypeParameters, IReadOnlyList<ITypeParameter> methodTypeParameters)
+		public GenericContext(IReadOnlyList<ITypeParameter>? classTypeParameters, IReadOnlyList<ITypeParameter>? methodTypeParameters)
 		{
 			this.ClassTypeParameters = classTypeParameters;
 			this.MethodTypeParameters = methodTypeParameters;

ICSharpCode.Decompiler/TypeSystem/TaskType.cs

@@ -17,6 +17,7 @@
 // DEALINGS IN THE SOFTWARE.
 
 using System;
+using System.Diagnostics.CodeAnalysis;
 
 namespace ICSharpCode.Decompiler.TypeSystem
 {
@@ -59,10 +60,10 @@ namespace ICSharpCode.Decompiler.TypeSystem
 		/// <summary>
 		/// Gets whether the specified type is a Task-like type.
 		/// </summary>
-		public static bool IsCustomTask(IType type, out IType? builderType)
+		public static bool IsCustomTask(IType type, [NotNullWhen(true)] out IType? builderType)
 		{
 			builderType = null;
-			ITypeDefinition def = type.GetDefinition();
+			ITypeDefinition? def = type.GetDefinition();
 			if (def != null)
 			{
 				if (def.TypeParameterCount > 1)

ILSpy/Analyzers/TreeNodes/AnalyzedEventTreeNode.cs

@@ -23,6 +23,8 @@ using ICSharpCode.ILSpy.TreeNodes;
 
 namespace ICSharpCode.ILSpy.Analyzers.TreeNodes
 {
+	using System.Diagnostics.CodeAnalysis;
+
 	using ICSharpCode.Decompiler.TypeSystem;
 	using ICSharpCode.ILSpyX.Analyzers;
 
@@ -68,7 +70,7 @@ namespace ICSharpCode.ILSpy.Analyzers.TreeNodes
 			}
 		}
 
-		bool TryFindBackingField(IEvent analyzedEvent, out IField backingField)
+		bool TryFindBackingField(IEvent analyzedEvent, [NotNullWhen(true)] out IField? backingField)
 		{
 			backingField = null;
 			foreach (var field in analyzedEvent.DeclaringTypeDefinition.GetFields(options: GetMemberOptions.IgnoreInheritedMembers))