Add return that doesn't take any value

codegen.c

@@ -506,8 +506,10 @@ static void gen(Node *node) {
     return;
   }
   case ND_RETURN:
-    gen(node->lhs);
-    printf("  pop rax\n");
+    if (node->lhs) {
+      gen(node->lhs);
+      printf("  pop rax\n");
+    }
     printf("  jmp .L.return.%s\n", funcname);
     return;
   case ND_CAST:

parse.c

@@ -1121,7 +1121,7 @@ static Node *stmt(void) {
   return node;
 }
 
-// stmt2 = "return" expr ";"
+// stmt2 = "return" expr? ";"
 //       | "if" "(" expr ")" stmt ("else" stmt)?
 //       | "switch" "(" expr ")" stmt
 //       | "case" const-expr ":" stmt
@@ -1139,6 +1139,9 @@ static Node *stmt(void) {
 static Node *stmt2(void) {
   Token *tok;
   if (tok = consume("return")) {
+    if (consume(";"))
+      return new_node(ND_RETURN, tok);
+
     Node *node = new_unary(ND_RETURN, expr(), tok);
     expect(";");
     return node;

tests

@@ -117,6 +117,10 @@ int fib(int x) {
   return fib(x-1) + fib(x-2);
 }
 
+void ret_none() {
+  return;
+}
+
 static int static_fn() { return 3; }
 
 int param_decay(int x[]) { return x[0]; }
@@ -678,6 +682,8 @@ int main() {
   assert(3, tree->lhs->lhs->val, "tree->lhs->lhs->val");
   assert(4, tree->lhs->rhs->val, "tree->lhs->rhs->val");
 
+  ret_none();
+
   printf("OK\n");
   return 0;
 }