chibicc - Simple c compiler for statement

What is changed to introduce for loop ?

No big changes on top of if statement feature.

For parser, add another grammar/production rule for for statement.

// stmt = "return" expr ";" 
//        | "{" compound_stmt
//        | expr_stmt
//        | "if" "(" expr ")" stmt ("else" stmt)?
//        | "for" "(" expr_stmt expr? ";" expr? ")" stmt 
static Node* stmt(Token**rest, Token* tok) {
  if(equal(tok, "return")) {
    Node* node = new_unary(ND_RETURN, expr(&tok, tok->next));
    *rest = skip(tok, ";");
    return node;
  }

  if(equal(tok, "{")) {
    return compound_stmt(rest, tok->next);
  }

  if(equal(tok, "if")) {
    tok = skip(tok->next, "(");
    Node* node = new_node(ND_IF);
    node->cond = expr(&tok, tok);
    tok = skip(tok, ")");
    node->then = stmt(&tok, tok);
    if(equal(tok, "else")) {
      node->els = stmt(&tok, tok->next);
    }
    *rest = tok;
    return node;
  }

  if(equal(tok, "for")) {
    tok = skip(tok->next, "(");
    Node* node = new_node(ND_FOR);
    node->init = expr_stmt(&tok, tok);
    if(!equal(tok, ";")) {
      node->cond = expr(&tok, tok);
    }
    tok = skip(tok, ";");

    if(!equal(tok, ")")) {
    node->inc = expr(&tok, tok);
    }
    tok = skip(tok, ")");
    node->then = stmt(&tok, tok);
    *rest = tok;
    return node;
  }

  return expr_stmt(rest, tok);
}

Introduce init and inc node inside of Node type to represent initialization and increment operation in for statement. for(init;cond; inc){}

typedef struct Node Node;
struct Node {
  NodeKind kind;
  Node* lhs; //left hand side
  Node* rhs; // right hand side
  Node* next; // next node
  Node* body; // {} body node

  // "if" or "for" statement
  Node* cond; 
  Node* then; 
  Node* els; 
  Node* init;
  Node* inc;


  // char name;
  Obj* obj; // used if kind == ND_VAR
  int val;  // used if kind == ND_NUM
};

For code generator, generate .L.begin.%d: to indicate the start of the for block. Use cmp $0, %%rax and jmp .L.end.%d after cond to go out of for block. Use jmp .L.begin.%d to jmp back to the begining of the for block at the end. And then comparison at the begining will decide whether to jump out of the for block or not.

  case ND_FOR: {
      int c = count_depth();
      gen_stmt(node->init);
      printf(".L.begin.%d:\n", c);
      if(node->cond) {
        gen_expr(node->cond);
        printf("  cmp $0, %%rax\n");
        printf("  je .L.end.%d\n",c);
      }

      gen_stmt(node->then);
      if(node->inc) {
        gen_expr(node->inc);
      }
      printf("  jmp .L.begin.%d\n",c);
      printf(".L.end.%d:\n",c);
      return;
    }

What is changed to introduce for loop ?

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