Turn block_return into IR instruction

WasmLib/Decompilation/Intermediate/Instructions/BlockReturnInstruction.cs

@@ -0,0 +1,21 @@
+using WasmLib.FileFormat;
+
+namespace WasmLib.Decompilation.Intermediate.Instructions
+{
+    public class BlockReturnInstruction : IntermediateInstruction
+    {
+        private readonly ValueKind type;
+
+        public BlockReturnInstruction(ValueKind type)
+        {
+            this.type = type;
+        }
+
+        public override ValueKind[] PopTypes => new[] {type};
+        public override ValueKind[] PushTypes => new ValueKind[0];
+        public override bool RestOfBlockUnreachable => true;
+        public override bool IsPure => false;
+
+        public override string OperationStringFormat => "block_return {0}";
+    }
+}

WasmLib/Decompilation/Intermediate/IntermediateConverter.cs

@@ -33,15 +33,19 @@ namespace WasmLib.Decompilation.Intermediate
             return block;
         }
 
-        private List<IntermediateInstruction> ConvertBlock(ref int i, bool allowElse = false)
+        private List<IntermediateInstruction> ConvertBlock(ref int i, bool allowElse = false, ValueKind blockReturnType = ValueKind.Empty)
         {
             var list = new List<IntermediateInstruction>();
+            bool reachable = true;
 
             for (; i < function.Instructions.Length; i++) {
                 Instruction instruction = function.Instructions[i];
                 switch (instruction.OpCode) {
                     case OpCode.End:
                     case OpCode.Else when allowElse:
+                        if (blockReturnType != ValueKind.Empty && reachable) {
+                            list.Add(new BlockReturnInstruction(blockReturnType));
+                        }
                         return list;
                     case OpCode.Else:
                         throw new Exception($"Unexpected `{instruction}` instruction, else is not allowed in the current block");
@@ -49,13 +53,13 @@ namespace WasmLib.Decompilation.Intermediate
                     case OpCode.Loop:
                     case OpCode.If:
                         i++;
-                        List<IntermediateInstruction> list1 = ConvertBlock(ref i, instruction.OpCode == OpCode.If);
+                        List<IntermediateInstruction> list1 = ConvertBlock(ref i, instruction.OpCode == OpCode.If, (ValueKind)instruction.UIntOperand);
                         List<IntermediateInstruction>? list2 = null;
 
                         var instr = function.Instructions[i];
                         if (instr.OpCode == OpCode.Else) {
                             i++;
-                            list2 = ConvertBlock(ref i);
+                            list2 = ConvertBlock(ref i, false, (ValueKind)instruction.UIntOperand);
                         }
                         else {
                             Debug.Assert(instr.OpCode == OpCode.End);
@@ -68,6 +72,10 @@ namespace WasmLib.Decompilation.Intermediate
 
                         if (intermediateInstruction != null) {
                             list.Add(intermediateInstruction);
+                            
+                            if (intermediateInstruction.RestOfBlockUnreachable) {
+                                reachable = false;
+                            } 
                         }
 
                         break;

WasmLib/Decompilation/IntermediateRepresentationDecompiler.cs

@@ -102,14 +102,7 @@ namespace WasmLib.Decompilation
                     HandleInstruction(ref context2, instr);
                 }
 
-                // if stack has values left on it, and we expect a return value
-                if (block.HasReturn && !context2.RestOfBlockUnreachable) {
-                    Debug.Assert(context2.StackIndices.Peek() != context2.Stack.Count);
-                    
-                    var popped = context2.Pop();
-                    Debug.Assert(popped.Type == block.ValueKind);
-                    context2.WriteFull($"block_return {popped}");
-                }
+                Debug.Assert(!(block.HasReturn && !context2.RestOfBlockUnreachable));
 
                 context2.ExitBlock();
             }