Support zero-arity function calls

chibicc.h

@@ -80,6 +80,7 @@ typedef enum {
   ND_IF,        // "if"
   ND_FOR,       // "for" or "while"
   ND_BLOCK,     // { ... }
+  ND_FUNCALL,   // Function call
   ND_EXPR_STMT, // Expression statement
   ND_VAR,       // Variable
   ND_NUM,       // Integer
@@ -105,6 +106,9 @@ struct Node {
   // Block
   Node *body;
 
+  // Function call
+  char *funcname;
+
   Obj *var;      // Used if kind == ND_VAR
   int val;       // Used if kind == ND_NUM
 };

codegen.c

@@ -68,6 +68,10 @@ static void gen_expr(Node *node) {
     pop("%rdi");
     printf("  mov %%rax, (%%rdi)\n");
     return;
+  case ND_FUNCALL:
+    printf("  mov $0, %%rax\n");
+    printf("  call %s\n", node->funcname);
+    return;
   }
 
   gen_expr(node->rhs);

parse.c

@@ -418,7 +418,8 @@ static Node *unary(Token **rest, Token *tok) {
   return primary(rest, tok);
 }
 
-// primary = "(" expr ")" | ident | num
+// primary = "(" expr ")" | ident args? | num
+// args = "(" ")"
 static Node *primary(Token **rest, Token *tok) {
   if (equal(tok, "(")) {
     Node *node = expr(&tok, tok->next);
@@ -427,6 +428,15 @@ static Node *primary(Token **rest, Token *tok) {
   }
 
   if (tok->kind == TK_IDENT) {
+    // Function call
+    if (equal(tok->next, "(")) {
+      Node *node = new_node(ND_FUNCALL, tok);
+      node->funcname = strndup(tok->loc, tok->len);
+      *rest = skip(tok->next->next, ")");
+      return node;
+    }
+
+    // Variable
     Obj *var = find_var(tok);
     if (!var)
       error_tok(tok, "undefined variable");

test.sh

@@ -1,10 +1,15 @@
 #!/bin/bash
+cat <<EOF | gcc -xc -c -o tmp2.o -
+int ret3() { return 3; }
+int ret5() { return 5; }
+EOF
+
 assert() {
   expected="$1"
   input="$2"
 
   ./chibicc "$input" > tmp.s || exit
-  gcc -static -o tmp tmp.s
+  gcc -static -o tmp tmp.s tmp2.o
   ./tmp
   actual="$?"
 
@@ -92,4 +97,7 @@ assert 5 '{ int x=3; return (&x+2)-&x+3; }'
 assert 8 '{ int x, y; x=3; y=5; return x+y; }'
 assert 8 '{ int x=3, y=5; return x+y; }'
 
+assert 3 '{ return ret3(); }'
+assert 5 '{ return ret5(); }'
+
 echo OK

type.c

@@ -42,6 +42,7 @@ void add_type(Node *node) {
   case ND_LT:
   case ND_LE:
   case ND_NUM:
+  case ND_FUNCALL:
     node->ty = ty_int;
     return;
   case ND_VAR: