Output pseudo-code in generic decompiler using generic IR names

WasmLib/Decompilation/GenericDecompiler.cs

@@ -5,9 +5,9 @@ using System.IO;
 using System.Linq;
 using Rivers;
 using Rivers.Analysis;
-using Rivers.Serialization.Dot;
 using WasmLib.Decompilation.Intermediate;
 using WasmLib.Decompilation.Intermediate.Graph;
+using WasmLib.Decompilation.SourceCode;
 using WasmLib.FileFormat;
 
 namespace WasmLib.Decompilation
@@ -27,9 +27,19 @@ namespace WasmLib.Decompilation
             FunctionSignature signature = WasmModule.FunctionTypes[WasmModule.Functions[functionIndex]];
             
             List<IntermediateInstruction> instructions = new IntermediateConverter(WasmModule, body, signature).Convert();
-            // TODO: add return instruction to intermediate
-            // TODO: add graph node for global state, locals or parameters?
 
+            Graph graph = CreateGraph(instructions);
+            
+            // TODO: remove subtrees with no side effects?
+
+            OutputAsCode(graph, output);
+            
+            // var writer = new DotWriter(output);
+            // writer.Write(graph);
+        }
+
+        private static Graph CreateGraph(IEnumerable<IntermediateInstruction> instructions)
+        {
             var graph = new Graph();
             var stack = new Stack<(InstructionNode, ValueKind)>();
 
@@ -42,32 +52,81 @@ namespace WasmLib.Decompilation
                 InstructionNode node = new InstructionNode(instruction, instructionNum++);
                 graph.Nodes.Add(node);
 
+                Debug.Assert(instruction.PushCount <= 1, "Instruction pushed multiple variables to stack, which shouldn't happen.");
                 for (int i = 0; i < instruction.PopCount; i++) {
                     (InstructionNode sourceInstruction, ValueKind type) = stack.Pop();
                     Debug.Assert(type == instruction.PopTypes[i]);
                     sourceInstruction.OutgoingEdges.Add(new StackVariableEdge(sourceInstruction, node, type));
                 }
+
                 for (int i = 0; i < instruction.PushCount; i++) {
                     stack.Push((node, instruction.PushTypes[i]));
                 }
 
                 // if this instruction is not pure, add a dependency on the last impure instruction, if any
                 // NOTE: this could possibly be optimized by having different kinds of impurity
-                if (!instruction.IsPure) {
-                    InstructionNode? dependentInstruction = graph.Nodes.Cast<InstructionNode>().Reverse().Skip(1).FirstOrDefault(x => !x.Instruction.IsPure);
+                // TODO: edges not required anymore for decompiled code output?
+                if (!node.IsPure) {
+                    InstructionNode? dependentInstruction = graph.Nodes.Cast<InstructionNode>().Reverse().Skip(1).FirstOrDefault(x => !x.IsPure);
                     dependentInstruction?.OutgoingEdges.Add(new ImpurityDependencyEdge(dependentInstruction, node));
                 }
             }
 
-            // this assert seems to fail, perhaps write own version in the future
+            // BUG: see Washi1337/Rivers#6
             // Debug.Assert(!graph.IsCyclic(), "Got cyclic dependency in function!");
-            Console.WriteLine(graph.IsCyclic());
+            if (!graph.IsConnected()) {
+                throw new NotImplementedException();
+            }
 
-            // TODO: get all nodes with no outgoing edges, write them out (taking into account side effects?)
-            // TODO: remove trees with no side effects
+            return graph;
+        }
 
-            var writer = new DotWriter(output, new DefaultUserDataSerializer());
-            writer.Write(graph);
+        private static void OutputAsCode(Graph graph, TextWriter output)
+        {
+            var varCounts = new Dictionary<ValueKind, int> {
+                {ValueKind.I32, 0},
+                {ValueKind.I64, 0},
+                {ValueKind.F32, 0},
+                {ValueKind.F64, 0},
+            };
+            
+            var statements = new Dictionary<int, Expression>();
+            foreach (var currentNode in graph.Nodes.OfType<InstructionNode>()) {
+                var parameterEdges = currentNode.IncomingVariableEdges.ToArray();
+
+                // only handle if node consumes variables
+                if (parameterEdges.Any()) {
+                    // for each dependency, check if it can be reached in a pure way
+                    // if so, inline it
+                    // if not, create intermediary statements
+                    var parameters = new Expression[parameterEdges.Length];
+                    for (int i = 0; i < parameterEdges.Length; i++) {
+                        var edge = parameterEdges[i];
+                        var variableNode = edge.Source;
+                        var isPure = !graph.Nodes.OfType<InstructionNode>().Any(x => !x.IsPure & x.Index > variableNode.Index && x.Index < currentNode.Index);
+
+                        if (isPure) { // TODO: and instruction can be inlined
+                            parameters[i] = statements[variableNode.Index];
+                            statements.Remove(variableNode.Index);
+                        }
+                        else {
+                            var assignment = new AssignmentExpression(statements[variableNode.Index], edge.Type, varCounts[edge.Type]++);
+                            statements[variableNode.Index] = assignment;
+                            parameters[i] = assignment.Reference;
+                        }
+                    }
+
+                    statements[currentNode.Index] = new GenericExpression(currentNode.Instruction, parameters);
+                }
+                else {
+                    statements[currentNode.Index] = new GenericExpression(currentNode.Instruction);
+                }
+
+            }
+
+            foreach (Expression expression in statements.Values) {
+                output.WriteLine(expression.GetStringRepresentation());
+            }
         }
     }
 }

WasmLib/Decompilation/Intermediate/Graph/InstructionNode.cs

@@ -1,4 +1,6 @@
+using System.Collections.Generic;
 using System.Diagnostics;
+using System.Linq;
 using Rivers;
 
 namespace WasmLib.Decompilation.Intermediate.Graph
@@ -6,10 +8,18 @@ namespace WasmLib.Decompilation.Intermediate.Graph
     public class InstructionNode : Node
     {
         public IntermediateInstruction Instruction { get; }
+        public int Index { get; }
+        public bool IsPure => Instruction.IsPure;
+
+        public IEnumerable<ImpurityDependencyEdge> OutgoingImpurityEdges => OutgoingEdges.OfType<ImpurityDependencyEdge>();
+        public IEnumerable<ImpurityDependencyEdge> IncomingImpurityEdges => IncomingEdges.OfType<ImpurityDependencyEdge>();
+        public IEnumerable<StackVariableEdge> OutgoingVariableEdges => OutgoingEdges.OfType<StackVariableEdge>();
+        public IEnumerable<StackVariableEdge> IncomingVariableEdges => IncomingEdges.OfType<StackVariableEdge>();
 
         public InstructionNode(IntermediateInstruction instruction, int idx) : base($"_{idx:X4}")
         {
             Instruction = instruction;
+            Index = idx;
             AddUserData();
         }
 
@@ -23,5 +33,7 @@ namespace WasmLib.Decompilation.Intermediate.Graph
                 ? $" {instructionString} "
                 : instructionString;
         }
+
+        public override string ToString() => Instruction.ToString();
     }
 }

WasmLib/Decompilation/SourceCode/AssignmentExpression.cs

@@ -0,0 +1,21 @@
+using WasmLib.FileFormat;
+using WasmLib.Utils;
+
+namespace WasmLib.Decompilation.SourceCode
+{
+    public class AssignmentExpression : Expression
+    {
+        public Expression BaseExpression { get; }
+        public VariableReferenceExpression Reference { get; }
+        public string Name { get; }
+
+        public AssignmentExpression(Expression baseExpression, ValueKind type, int index)
+        {
+            BaseExpression = baseExpression;
+            Name = $"{EnumUtils.GetDescription(type)}_{index}";
+            Reference = new VariableReferenceExpression(Name);
+        }
+
+        public override string GetStringRepresentation() => $"{Reference.GetStringRepresentation()} = {BaseExpression}";
+    }
+}

WasmLib/Decompilation/SourceCode/Expression.cs

@@ -0,0 +1,9 @@
+namespace WasmLib.Decompilation.SourceCode
+{
+    public abstract class Expression
+    {
+        public abstract string GetStringRepresentation();
+
+        public override string ToString() => GetStringRepresentation();
+    }
+}

WasmLib/Decompilation/SourceCode/GenericExpression.cs

@@ -0,0 +1,21 @@
+using System.Linq;
+using WasmLib.Decompilation.Intermediate;
+
+namespace WasmLib.Decompilation.SourceCode
+{
+    public class GenericExpression : Expression
+    {
+        public IntermediateInstruction BaseInstruction { get; }
+        public Expression[]? Parameters { get; }
+
+        public GenericExpression(IntermediateInstruction baseInstruction, Expression[]? parameters = null)
+        {
+            BaseInstruction = baseInstruction;
+            Parameters = parameters;
+        }
+
+        public override string GetStringRepresentation() => Parameters is null
+            ? BaseInstruction.ToString()
+            : $"{BaseInstruction}({string.Join(", ", Parameters.Reverse().Select(x => x.GetStringRepresentation()))})";
+    }
+}

WasmLib/Decompilation/SourceCode/VariableReferenceExpression.cs

@@ -0,0 +1,14 @@
+namespace WasmLib.Decompilation.SourceCode
+{
+    public class VariableReferenceExpression : Expression
+    {
+        public string Name { get; }
+
+        public VariableReferenceExpression(string name)
+        {
+            Name = name;
+        }
+
+        public override string GetStringRepresentation() => Name;
+    }
+}