Add "if" statement

chibicc.h

@@ -72,6 +72,7 @@ typedef enum {
   ND_LE,        // <=
   ND_ASSIGN,    // =
   ND_RETURN,    // "return"
+  ND_IF,        // "if"
   ND_BLOCK,     // { ... }
   ND_EXPR_STMT, // Expression statement
   ND_VAR,       // Variable
@@ -82,9 +83,15 @@ typedef enum {
 struct Node {
   NodeKind kind; // Node kind
   Node *next;    // Next node
+
   Node *lhs;     // Left-hand side
   Node *rhs;     // Right-hand side
 
+  // "if" statement
+  Node *cond;
+  Node *then;
+  Node *els;
+
   // Block
   Node *body;
 

codegen.c

@@ -2,6 +2,11 @@
 
 static int depth;
 
+static int count(void) {
+  static int i = 1;
+  return i++;
+}
+
 static void push(void) {
   printf("  push %%rax\n");
   depth++;
@@ -95,6 +100,19 @@ static void gen_expr(Node *node) {
 
 static void gen_stmt(Node *node) {
   switch (node->kind) {
+  case ND_IF: {
+    int c = count();
+    gen_expr(node->cond);
+    printf("  cmp $0, %%rax\n");
+    printf("  je  .L.else.%d\n", c);
+    gen_stmt(node->then);
+    printf("  jmp .L.end.%d\n", c);
+    printf(".L.else.%d:\n", c);
+    if (node->els)
+      gen_stmt(node->els);
+    printf(".L.end.%d:\n", c);
+    return;
+  }
   case ND_BLOCK:
     for (Node *n = node->body; n; n = n->next)
       gen_stmt(n);

parse.c

@@ -63,6 +63,7 @@ static Obj *new_lvar(char *name) {
 }
 
 // stmt = "return" expr ";"
+//      | "if" "(" expr ")" stmt ("else" stmt)?
 //      | "{" compound-stmt
 //      | expr-stmt
 static Node *stmt(Token **rest, Token *tok) {
@@ -72,6 +73,18 @@ static Node *stmt(Token **rest, Token *tok) {
     return node;
   }
 
+  if (equal(tok, "if")) {
+    Node *node = new_node(ND_IF);
+    tok = skip(tok->next, "(");
+    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, "{"))
     return compound_stmt(rest, tok->next);
 

test.sh

@@ -62,4 +62,11 @@ assert 3 '{ 1; 2; return 3; }'
 assert 3 '{ {1; {2;} return 3;} }'
 assert 5 '{ ;;; return 5; }'
 
+assert 3 '{ if (0) return 2; return 3; }'
+assert 3 '{ if (1-1) return 2; return 3; }'
+assert 2 '{ if (1) return 2; return 3; }'
+assert 2 '{ if (2-1) return 2; return 3; }'
+assert 4 '{ if (0) { 1; 2; return 3; } else { return 4; } }'
+assert 3 '{ if (1) { 1; 2; return 3; } else { return 4; } }'
+
 echo OK

tokenize.c

@@ -79,9 +79,18 @@ static int read_punct(char *p) {
   return ispunct(*p) ? 1 : 0;
 }
 
+static bool is_keyword(Token *tok) {
+  static char *kw[] = {"return", "if", "else"};
+
+  for (int i = 0; i < sizeof(kw) / sizeof(*kw); i++)
+    if (equal(tok, kw[i]))
+      return true;
+  return false;
+}
+
 static void convert_keywords(Token *tok) {
   for (Token *t = tok; t->kind != TK_EOF; t = t->next)
-    if (equal(t, "return"))
+    if (is_keyword(t))
       t->kind = TK_KEYWORD;
 }