ps5: generate_return_statement and fix epilogue

ps5/src/emit.h

@@ -51,6 +51,8 @@
 
 #define CMPQ(op1, op2) EMIT("cmpq %s, %s", (op1), (op2)) // Compare the two operands
 
+#define CLEAR(reg) EMIT("xor %s, %s", (reg), (reg))
+
 // The SETcc-family of instructions assigns either 0 or 1 to a byte register, based on a comparison.
 // The instruction immediately before the SETcc should be a
 //   cmpq op1, op2

ps5/src/generator.c

@@ -154,6 +154,7 @@ static void generate_function(symbol_t* function)
   generate_statement(function->node);
 
   // TODO (Task 3.2): Emit the epilogue, including a label and a default return value (0)
+  CLEAR(RAX);
   LABEL(".%s.epilogue", function->name);
   MOVQ(RBP, RSP);
   POPQ(RBP);
@@ -337,6 +338,10 @@ static void generate_print_statement(node_t* statement)
 static void generate_return_statement(node_t* statement)
 {
   // TODO (Task 4.5): Evaluate the return value, store it in %rax and jump to the function epilogue
+  generate_expression(statement->children[0]);
+  char epilogue[64];
+  snprintf(epilogue, sizeof(epilogue), ".%s.epilogue", current_function->name);
+  JMP(epilogue);
 }
 
 // Recursively generate the given statement node, and all sub-statements.