Add Block.FinalInstruction

ICSharpCode.Decompiler/CSharp/StatementBuilder.cs

@@ -145,6 +145,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			foreach (var inst in block.Instructions) {
 				blockStatement.Add(Convert(inst));
 			}
+			blockStatement.Add(Convert(block.FinalInstruction));
 			return blockStatement;
 		}
 		
@@ -159,6 +160,9 @@ namespace ICSharpCode.Decompiler.CSharp
 				foreach (var inst in block.Instructions) {
 					blockStatement.Add(Convert(inst));
 				}
+				if (block.FinalInstruction.OpCode != OpCode.Nop) {
+					blockStatement.Add(Convert(block.FinalInstruction));
+				}
 			}
 			return blockStatement;
 		}

ICSharpCode.Decompiler/IL/Instructions/Block.cs

@@ -35,21 +35,17 @@ namespace ICSharpCode.Decompiler.IL
 	/// </para>
 	/// <code>
 	///   foreach (var inst in Instructions) {
-	///     inst.Phase1();
-	///     var result = inst.Phase2();
+	///     var result = inst.Phase1().Phase2();
 	///     if (result != void) evalStack.Push(result);
 	///   }
+	///   return FinalInstruction.Phase1().Phase2();
 	/// </code>
 	/// <para>
-	/// If the execution reaches the end of the block, the block returns the result value of the last instruction.
+	/// Note: if execution reaches the end of the instruction list,
+	/// the FinalInstruction (which is not part of the list) will be executed.
+	/// The block returns returns the result value of the FinalInstruction.
+	/// For blocks returning void, the FinalInstruction will usually be 'nop'.
 	/// </para>
-	/// TODO: actually I think it's a good idea to implement a small ILAst interpreter
-	///    public virtual ILInstruction Phase1(InterpreterState state);
-	///    public virtual InterpreterResult ILInstruction Phase2(InterpreterState state);
-	/// It's probably the easiest solution for specifying clear semantics, and
-	/// we might be able to use the interpreter logic for symbolic execution.
-	/// In fact, I think we'll need at least Phase1() in order to implement TransformStackIntoVariablesState()
-	/// without being incorrect about the pop-order in nested blocks.
 	/// </summary>
 	/// <remarks>
 	/// Fun fact: the empty block acts like a phase-2 pop instruction,
@@ -57,23 +53,32 @@ namespace ICSharpCode.Decompiler.IL
 	/// However, this is just of theoretical interest; we currently don't plan to use inline blocks that
 	/// pop elements that they didn't push themselves.
 	/// </remarks>
-	partial class Block : ILInstruction, IEnumerable<ILInstruction>
+	partial class Block : ILInstruction
 	{
 		public readonly InstructionCollection<ILInstruction> Instructions;
+		ILInstruction finalInstruction;
+
+		public ILInstruction FinalInstruction {
+			get {
+				return finalInstruction;
+			}
+			set {
+				ValidateChild(value);
+				SetChildInstruction(ref finalInstruction, value);
+			}
+		}
 		
 		public int IncomingEdgeCount;
 		
 		public Block() : base(OpCode.Block)
 		{
 			this.Instructions = new InstructionCollection<ILInstruction>(this);
+			this.FinalInstruction = new Nop();
 		}
 		
 		public override StackType ResultType {
 			get {
-				if (Instructions.Count == 0)
-					return StackType.Void;
-				else
-					return Instructions.Last().ResultType;
+				return finalInstruction.ResultType;
 			}
 		}
 		
@@ -97,12 +102,21 @@ namespace ICSharpCode.Decompiler.IL
 				inst.WriteTo(output);
 				output.WriteLine();
 			}
+			if (finalInstruction.OpCode != OpCode.Nop) {
+				output.Write("final: ");
+				finalInstruction.WriteTo(output);
+				output.WriteLine();
+			}
 			output.Unindent();
 			output.Write("}");
 		}
 		
 		public override IEnumerable<ILInstruction> Children {
-			get { return Instructions; }
+			get {
+				foreach (var inst in Instructions)
+					yield return inst;
+				yield return finalInstruction;
+			}
 		}
 		
 		public override void TransformChildren(ILVisitor<ILInstruction> visitor)
@@ -110,22 +124,21 @@ namespace ICSharpCode.Decompiler.IL
 			for (int i = 0; i < Instructions.Count; i++) {
 				Instructions[i] = Instructions[i].AcceptVisitor(visitor);
 			}
+			FinalInstruction = FinalInstruction.AcceptVisitor(visitor);
 		}
 		
 		protected override InstructionFlags ComputeFlags()
 		{
 			var flags = InstructionFlags.None;
 			foreach (var inst in Instructions) {
-				flags |= inst.Flags;
+				flags |= Phase1Boundary(inst.Flags);
 				if (inst.ResultType != StackType.Void) {
 					// implicit push
 					flags |= InstructionFlags.MayWriteEvaluationStack;
 				}
 			}
-			// implicit pop at end of block
-			if ((flags & InstructionFlags.EndPointUnreachable) == 0)
-				flags |= InstructionFlags.MayWriteEvaluationStack;
-			return Phase1Boundary(flags);
+			flags |= Phase1Boundary(FinalInstruction.Flags);
+			return flags;
 		}
 		
 		/// <summary>
@@ -150,21 +163,5 @@ namespace ICSharpCode.Decompiler.IL
 			// an inline block has no phase-1 effects, so we're immediately done with inlining
 			return this;
 		}
-		
-		// Add() and GetEnumerator() for collection initializer support:
-		public void Add(ILInstruction instruction)
-		{
-			this.Instructions.Add(instruction);
-		}
-		
-		IEnumerator<ILInstruction> IEnumerable<ILInstruction>.GetEnumerator()
-		{
-			return this.Instructions.GetEnumerator();
-		}
-		
-		System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
-		{
-			return this.Instructions.GetEnumerator();
-		}
 	}
 }

ICSharpCode.Decompiler/IL/TransformingVisitor.cs

@@ -87,23 +87,32 @@ namespace ICSharpCode.Decompiler.IL
 			}
 		}
 		
+		ILInstruction DoInline(InliningStack stack, ILInstruction inst)
+		{
+			do {
+				inst = inst.AcceptVisitor(this);
+				stack.didInline = false;
+				stack.error = false;
+				inst = inst.Inline(InstructionFlags.None, stack);
+				Debug.Assert(stack.error == inst.HasFlag(InstructionFlags.MayPeek | InstructionFlags.MayPop));
+			} while (stack.didInline); // repeat transformations when something was inlined
+			return inst;
+		}
+		
 		protected internal override ILInstruction VisitBlock(Block block)
 		{
 			var stack = new InliningStack();
 			List<ILInstruction> output = new List<ILInstruction>();
 			for (int i = 0; i < block.Instructions.Count; i++) {
 				var inst = block.Instructions[i];
-				do {
-					inst = inst.AcceptVisitor(this);
-					stack.didInline = false;
-					stack.error = false;
-					inst = inst.Inline(InstructionFlags.None, stack);
-					Debug.Assert(stack.error == inst.HasFlag(InstructionFlags.MayPeek | InstructionFlags.MayPop));
-				} while (stack.didInline); // repeat transformations when something was inlined
-				if (stack.error || inst.HasFlag(InstructionFlags.MayBranch)) {
+				inst = DoInline(stack, inst); 
+				if (inst.HasFlag(InstructionFlags.MayBranch 
+				                 | InstructionFlags.MayPeek | InstructionFlags.MayPop
+				                 | InstructionFlags.MayReadEvaluationStack | InstructionFlags.MayWriteEvaluationStack)) {
 					// Values currently on the stack might be used on both sides of the branch,
 					// so we can't inline them.
-					// We also have to flush the stack if some occurrence of 'pop' or 'peek' remains in the current instruction.
+					// We also have to flush the stack if the instruction still accesses the evaluation stack,
+					// no matter whether in phase-1 or phase-2.
 					FlushInstructionStack(stack, output);
 				}
 				if (inst.ResultType == StackType.Void) {
@@ -132,14 +141,13 @@ namespace ICSharpCode.Decompiler.IL
 					stack.Push(inst);
 				}
 			}
+			// Allow inlining into the final instruction
+			block.FinalInstruction = DoInline(stack, block.FinalInstruction);
 			FlushInstructionStack(stack, output);
+			block.Instructions.ReplaceList(output);
 			if (!(block.Parent is BlockContainer)) {
-				// We can't unpack an instruction from a block if there's the potential that this changes
-				// the pop-order in the phase 1 evaluation of the parent block.
-				if (output.Count == 1 && !output[0].HasFlag(InstructionFlags.MayPeek | InstructionFlags.MayPop))
-					return output[0];
+				return TrySimplifyBlock(block);
 			}
-			block.Instructions.ReplaceList(output);
 			return block;
 		}
 
@@ -160,14 +168,26 @@ namespace ICSharpCode.Decompiler.IL
 			// If the container only contains a single block, and the block contents do not jump back to the block start,
 			// we can remove the container.
 			if (container.Blocks.Count == 1 && container.EntryPoint.IncomingEdgeCount == 1) {
-				// If the block has only one instruction, we can remove the block too
-				// (but only if this doesn't change the pop-order in the phase 1 evaluation of the parent block)
-				var instructions = container.EntryPoint.Instructions;
-				if (instructions.Count == 1 && !instructions[0].HasFlag(InstructionFlags.MayPeek | InstructionFlags.MayPop))
-					return instructions[0];
-				return container.EntryPoint;
+				return TrySimplifyBlock(container.EntryPoint);
 			}
 			return container;
 		}
+		
+		/// <summary>
+		/// If a block has only one instruction, replace it with that instruction.
+		/// </summary>
+		ILInstruction TrySimplifyBlock(Block block)
+		{
+			// If the block has only one instruction, we can remove the block too
+			// (but only if this doesn't change the pop-order in the phase 1 evaluation of the parent block)
+			if (block.Instructions.Count == 0) {
+				if (!block.FinalInstruction.HasFlag(InstructionFlags.MayPeek | InstructionFlags.MayPop))
+					return block.FinalInstruction;
+			} else if (block.Instructions.Count == 1 && block.FinalInstruction.OpCode == OpCode.Nop) {
+				if (block.Instructions[0].ResultType == StackType.Void && !block.Instructions[0].HasFlag(InstructionFlags.MayPeek | InstructionFlags.MayPop))
+					return block.Instructions[0];
+			}
+			return block;
+		}
 	}
 }

ICSharpCode.Decompiler/Tests/ILTransforms/Inlining.cs

@@ -39,13 +39,19 @@ namespace ICSharpCode.Decompiler.Tests.ILTransforms
 		{
 			var f = MakeFunction(
 				new Block {
-					new LdcI4(1),
-					new LdcI4(2),
-					new Add(new Pop(StackType.I4), new Pop(StackType.I4), false, Sign.Signed)
+					Instructions = {
+						new LdcI4(1),
+						new LdcI4(2),
+						new Add(new Pop(StackType.I4), new Pop(StackType.I4), false, Sign.Signed)
+					}
 				});
 			f.AcceptVisitor(new TransformingVisitor());
 			Assert.AreEqual(
-				new Add(new LdcI4(1), new LdcI4(2), false, Sign.Signed).ToString(),
+				new Block {
+					Instructions = {
+						new Add(new LdcI4(1), new LdcI4(2), false, Sign.Signed)
+					}
+				}.ToString(),
 				f.Body.ToString()
 			);
 		}
@@ -55,26 +61,30 @@ namespace ICSharpCode.Decompiler.Tests.ILTransforms
 		{
 			var f = MakeFunction(
 				new Block {
-					new LdcI4(1),
-					new LdcI4(2),
-					new LdcI4(3),
-					new Call(TypeSystem.Action<int, int, int>()) {
-						Arguments = {
-							new Pop(StackType.I4),
-							new Block { new Pop(StackType.I4) },
-							new Pop(StackType.I4),
+					Instructions = {
+						new LdcI4(1),
+						new LdcI4(2),
+						new LdcI4(3),
+						new Call(TypeSystem.Action<int, int, int>()) {
+							Arguments = {
+								new Pop(StackType.I4),
+								new Block { FinalInstruction = new Pop(StackType.I4) },
+								new Pop(StackType.I4),
+							}
 						}
 					}
 				});
 			f.AcceptVisitor(new TransformingVisitor());
 			Assert.AreEqual(
 				new Block {
-					new LdcI4(1),
-					new Call(TypeSystem.Action<int, int, int>()) {
-						Arguments = {
-							new LdcI4(2),
-							new Block { new Pop(StackType.I4) },
-							new LdcI4(3)
+					Instructions = {
+						new LdcI4(1),
+						new Call(TypeSystem.Action<int, int, int>()) {
+							Arguments = {
+								new LdcI4(2),
+								new Block { FinalInstruction = new Pop(StackType.I4) },
+								new LdcI4(3)
+							}
 						}
 					}
 				}.ToString(),