[async] Fix await decompiler for pre-roslyn csc, at least in cases where the stack is empty during the await.

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -1760,7 +1760,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			}
 			return new UnaryOperatorExpression(UnaryOperatorType.Await, value.Expression)
 				.WithILInstruction(inst)
-				.WithRR(new ResolveResult(inst?.GetResultMethod.ReturnType ?? SpecialType.UnknownType));
+				.WithRR(new ResolveResult(inst.GetResultMethod?.ReturnType ?? SpecialType.UnknownType));
 		}
 
 		protected internal override TranslatedExpression VisitInvalidBranch(InvalidBranch inst, TranslationContext context)

ICSharpCode.Decompiler/IL/ControlFlow/AsyncAwaitDecompiler.cs

@@ -81,11 +81,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			}
 
 			InlineBodyOfMoveNext(function);
-
+			CleanUpBodyOfMoveNext(function);
-			// Copy-propagate temporaries holding a copy of 'this'.
-			foreach (var stloc in function.Descendants.OfType<StLoc>().Where(s => s.Variable.IsSingleDefinition && s.Value.MatchLdThis()).ToList()) {
-				CopyPropagation.Propagate(stloc, context);
-			}
 
 			AnalyzeStateMachine(function);
 			DetectAwaitPattern(function);
@@ -101,6 +97,26 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			function.RunTransforms(CSharpDecompiler.EarlyILTransforms(), context);
 		}
 
+		private void CleanUpBodyOfMoveNext(ILFunction function)
+		{
+			context.StepStartGroup("CleanUpBodyOfMoveNext", function);
+			// Simplify stobj(ldloca) -> stloc
+			foreach (var stobj in function.Descendants.OfType<StObj>()) {
+				ExpressionTransforms.StObjToStLoc(stobj, context);
+			}
+
+			// Copy-propagate temporaries holding a copy of 'this'.
+			foreach (var stloc in function.Descendants.OfType<StLoc>().Where(s => s.Variable.IsSingleDefinition && s.Value.MatchLdThis()).ToList()) {
+				CopyPropagation.Propagate(stloc, context);
+			}
+			new RemoveDeadVariableInit().Run(function, context);
+			// Run inlining, but don't remove dead variables (they might get revived by TranslateFieldsToLocalAccess)
+			foreach (var block in function.Descendants.OfType<Block>()) {
+				ILInlining.InlineAllInBlock(block, context);
+			}
+			context.StepEndGroup();
+		}
+
 		#region MatchTaskCreationPattern
 		bool MatchTaskCreationPattern(ILFunction function)
 		{
@@ -717,7 +733,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 				pos++;
 			}
 			if (block.Instructions[pos] is StLoc stlocCachedState) {
-				if (stlocCachedState.Variable.Kind == VariableKind.Local && stlocCachedState.Variable.Index == cachedStateVar.Index) { 
+				if (stlocCachedState.Variable.Kind == VariableKind.Local && stlocCachedState.Variable.Index == cachedStateVar?.Index) { 
 					if (stlocCachedState.Value.MatchLdLoc(m1Var) || stlocCachedState.Value.MatchLdcI4(initialState))
 						pos++;
 				}

ICSharpCode.Decompiler/IL/Transforms/ExpressionTransforms.cs

@@ -237,7 +237,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				&& TypeUtils.IsCompatibleTypeForMemoryAccess(new ByReferenceType(v.Type), inst.Type)
 				&& inst.UnalignedPrefix == 0
 				&& !inst.IsVolatile) {
-				context.Step("stobj(ldloca(v), ...) => stloc(v, ...)", inst);
+				context.Step($"stobj(ldloca {v.Name}, ...) => stloc {v.Name}(...)", inst);
 				inst.ReplaceWith(new StLoc(v, inst.Value));
 				return true;
 			}

ICSharpCode.Decompiler/IL/Transforms/ILInlining.cs

@@ -28,24 +28,20 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 	/// </summary>
 	public class ILInlining : IILTransform, IBlockTransform
 	{
-		ILTransformContext context;
-
 		public void Run(ILFunction function, ILTransformContext context)
 		{
-			this.context = context;
 			foreach (var block in function.Descendants.OfType<Block>()) {
-				InlineAllInBlock(block);
+				InlineAllInBlock(block, context);
 			}
 			function.Variables.RemoveDead();
 		}
 
 		public void Run(Block block, BlockTransformContext context)
 		{
-			this.context = context;
+			InlineAllInBlock(block, context);
-			InlineAllInBlock(block);
 		}
 
-		public bool InlineAllInBlock(Block block)
+		public static bool InlineAllInBlock(Block block, ILTransformContext context)
 		{
 			bool modified = false;
 			int i = 0;