Merge pull request #10 from CompilerProgramming/refactor

Revise the return instruction

Author: dibyendumajumdar

optvm/src/main/java/com/compilerprogramming/ezlang/compiler/CompiledFunction.java

@@ -39,7 +39,7 @@ public class CompiledFunction {
     public CompiledFunction(Symbol.FunctionTypeSymbol functionSymbol) {
         AST.FuncDecl funcDecl = (AST.FuncDecl) functionSymbol.functionDecl;
         this.functionType = (Type.TypeFunction) functionSymbol.type;
-        this.registerPool = new RegisterPool("%ret", functionType == null?null:functionType.returnType);
+        this.registerPool = new RegisterPool();
         setVirtualRegisters(funcDecl.scope);
         this.bid = 0;
         this.entry = this.currentBlock = createBlock();
@@ -54,7 +54,7 @@ public CompiledFunction(Symbol.FunctionTypeSymbol functionSymbol) {
 
     public CompiledFunction(Type.TypeFunction functionType) {
         this.functionType = (Type.TypeFunction) functionType;
-        this.registerPool = new RegisterPool("%ret", functionType == null?null:functionType.returnType);
+        this.registerPool = new RegisterPool();
         this.bid = 0;
         this.entry = this.currentBlock = createBlock();
         this.exit = createBlock();
@@ -115,7 +115,7 @@ private void compileReturn(AST.ReturnStmt returnStmt) {
             if (isIndexed)
                 codeIndexedLoad();
             if (virtualStack.size() == 1)
-                code(new Instruction.Return(pop(), registerPool.returnRegister));
+                code(new Instruction.Ret(pop()));
             else if (virtualStack.size() > 1)
                 throw new CompilerException("Virtual stack has more than one item at return");
         }

optvm/src/main/java/com/compilerprogramming/ezlang/compiler/Instruction.java

@@ -347,9 +347,32 @@ public StringBuilder toStr(StringBuilder sb) {
                     .append(sourceOperand);
         }
     }
-    public static class Return extends Move {
-        public Return(Operand from, Register reg) {
-            super(from, new Operand.ReturnRegisterOperand(reg));
+    public static class Ret extends Instruction {
+        public final Operand value;
+        public Ret(Operand value) {
+            this.value = value;
+        }
+        @Override
+        public boolean usesVars() {
+            return value != null && value instanceof Operand.RegisterOperand registerOperand;
+        }
+        @Override
+        public List<Register> uses() {
+            if (value != null && value instanceof Operand.RegisterOperand registerOperand)
+                return List.of(registerOperand.reg);
+            return Collections.emptyList();
+        }
+        @Override
+        public void replaceUses(Register[] newUses) {
+            if (newUses.length > 0)
+                value.replaceRegister(newUses[0]);
+        }
+        @Override
+        public StringBuilder toStr(StringBuilder sb) {
+            sb.append("ret");
+            if (value != null)
+                sb.append(" ").append(value);
+            return sb;
         }
     }
     public static class Unary extends Instruction {

optvm/src/main/java/com/compilerprogramming/ezlang/compiler/RegisterPool.java

@@ -14,14 +14,7 @@
  */
 public class RegisterPool {
     private final ArrayList<Register> registers = new ArrayList<>();
-    public final Register returnRegister;
 
-    public RegisterPool(String returnVarName, Type type) {
-        if (type != null)
-            returnRegister = newReg(returnVarName, type);
-        else
-            returnRegister = null;
-    }
     public Register getReg(int regNumber) {
         return registers.get(regNumber);
     }

optvm/src/main/java/com/compilerprogramming/ezlang/interpreter/Interpreter.java

@@ -44,16 +44,17 @@ public Value interpret(ExecutionStack execStack, Frame frame) {
             ip++;
             instruction = currentBlock.instructions.get(ip);
             switch (instruction) {
-                case Instruction.Return returnInst -> {
-                    if (returnInst.from instanceof Operand.ConstantOperand constantOperand) {
+                case Instruction.Ret retInst -> {
+                    if (retInst.value instanceof Operand.ConstantOperand constantOperand) {
                         execStack.stack[base] = new Value.IntegerValue(constantOperand.value);
                     }
-                    else if (returnInst.from instanceof Operand.RegisterOperand registerOperand) {
+                    else if (retInst.value instanceof Operand.RegisterOperand registerOperand) {
                         execStack.stack[base] = execStack.stack[base+registerOperand.slot()];
                     }
                     else throw new IllegalStateException();
                     returnValue = execStack.stack[base];
                 }
+
                 case Instruction.Move moveInst -> {
                     if (moveInst.to instanceof Operand.RegisterOperand toReg) {
                         if (moveInst.from instanceof Operand.RegisterOperand fromReg) {
@@ -98,11 +99,7 @@ else if (cbrInst.condition instanceof Operand.ConstantOperand constantOperand) {
                 case Instruction.Call callInst -> {
                     // Copy args to new frame
                     int baseReg = base+currentFunction.frameSize();
-                    int offset = 0;
-                    // In this version return reg
-                    if (!(callInst.callee.returnType instanceof Type.TypeVoid))
-                        offset = 1;
-                    int reg = baseReg + offset;
+                    int reg = baseReg;
                     for (Operand.RegisterOperand arg: callInst.args) {
                         execStack.stack[base + reg] = execStack.stack[base + arg.slot()];
                         reg += 1;