More aggressively duplicate return blocks in MoveNext() methods.

This fixes 'yield return' decompilation of debug builds using legacy csc.

ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs

@@ -51,10 +51,12 @@ namespace ICSharpCode.Decompiler.CSharp
 		/// <summary>
 		/// Pre-yield/await transforms.
 		/// </summary>
-		internal static List<IILTransform> EarlyILTransforms()
+		internal static List<IILTransform> EarlyILTransforms(bool aggressivelyDuplicateReturnBlocks = false)
 		{
 			return new List<IILTransform> {
-				new ControlFlowSimplification(),
+				new ControlFlowSimplification {
+					aggressivelyDuplicateReturnBlocks = aggressivelyDuplicateReturnBlocks
+				},
 				new SplitVariables(),
 				new ILInlining(),
 			};

ICSharpCode.Decompiler/IL/ControlFlow/ControlFlowSimplification.cs

@@ -36,6 +36,8 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 	/// </remarks>
 	public class ControlFlowSimplification : IILTransform
 	{
+		internal bool aggressivelyDuplicateReturnBlocks;
+
 		public void Run(ILFunction function, ILTransformContext context)
 		{
 			foreach (var block in function.Descendants.OfType<Block>()) {
@@ -129,12 +131,13 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			}
 		}
 
-		static bool ShouldSimplifyBranchToReturnBlock(Branch branch)
+		bool ShouldSimplifyBranchToReturnBlock(Branch branch)
 		{
 			var targetBlock = branch.TargetBlock;
 			if (targetBlock.Instructions.Count != 1 || targetBlock.FinalInstruction.OpCode != OpCode.Nop)
 				return false;
-			if (targetBlock.Parent == branch.Ancestors.OfType<BlockContainer>().FirstOrDefault()) {
+			if (targetBlock.Parent == branch.Ancestors.OfType<BlockContainer>().FirstOrDefault()
+				&& !aggressivelyDuplicateReturnBlocks) {
 				// only simplify when jumping out of a try-finally
 				return false;
 			}

ICSharpCode.Decompiler/IL/ControlFlow/YieldReturnDecompiler.cs

@@ -311,7 +311,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 				);
 			}
 			var il = new ILReader(typeSystem).ReadIL(method.Body, context.CancellationToken);
-			il.RunTransforms(CSharpDecompiler.EarlyILTransforms(), new ILTransformContext {
+			il.RunTransforms(CSharpDecompiler.EarlyILTransforms(true), new ILTransformContext {
 				Settings = context.Settings,
 				CancellationToken = context.CancellationToken,
 				TypeSystem = context.TypeSystem