Add +=, -=, *= and /=

parse.c

@@ -80,6 +80,8 @@ static Node *assign(Token **rest, Token *tok);
 static Node *equality(Token **rest, Token *tok);
 static Node *relational(Token **rest, Token *tok);
 static Node *add(Token **rest, Token *tok);
+static Node *new_add(Node *lhs, Node *rhs, Token *tok);
+static Node *new_sub(Node *lhs, Node *rhs, Token *tok);
 static Node *mul(Token **rest, Token *tok);
 static Node *cast(Token **rest, Token *tok);
 static Type *struct_decl(Token **rest, Token *tok);
@@ -670,13 +672,50 @@ static Node *expr(Token **rest, Token *tok) {
   return node;
 }
 
-// assign = equality ("=" assign)?
+// Convert `A op= B` to `tmp = &A, *tmp = *tmp op B`
+// where tmp is a fresh pointer variable.
+static Node *to_assign(Node *binary) {
+  add_type(binary->lhs);
+  add_type(binary->rhs);
+  Token *tok = binary->tok;
+
+  Obj *var = new_lvar("", pointer_to(binary->lhs->ty));
+
+  Node *expr1 = new_binary(ND_ASSIGN, new_var_node(var, tok),
+                           new_unary(ND_ADDR, binary->lhs, tok), tok);
+
+  Node *expr2 =
+    new_binary(ND_ASSIGN,
+               new_unary(ND_DEREF, new_var_node(var, tok), tok),
+               new_binary(binary->kind,
+                          new_unary(ND_DEREF, new_var_node(var, tok), tok),
+                          binary->rhs,
+                          tok),
+               tok);
+
+  return new_binary(ND_COMMA, expr1, expr2, tok);
+}
+
+// assign    = equality (assign-op assign)?
+// assign-op = "=" | "+=" | "-=" | "*=" | "/="
 static Node *assign(Token **rest, Token *tok) {
   Node *node = equality(&tok, tok);
 
   if (equal(tok, "="))
     return new_binary(ND_ASSIGN, node, assign(rest, tok->next), tok);
 
+  if (equal(tok, "+="))
+    return to_assign(new_add(node, assign(rest, tok->next), tok));
+
+  if (equal(tok, "-="))
+    return to_assign(new_sub(node, assign(rest, tok->next), tok));
+
+  if (equal(tok, "*="))
+    return to_assign(new_binary(ND_MUL, node, assign(rest, tok->next), tok));
+
+  if (equal(tok, "/="))
+    return to_assign(new_binary(ND_DIV, node, assign(rest, tok->next), tok));
+
   *rest = tok;
   return node;
 }

test/arith.c

@@ -33,6 +33,15 @@ int main() {
 
   ASSERT(0, 1073741824 * 100 / 100);
 
+  ASSERT(7, ({ int i=2; i+=5; i; }));
+  ASSERT(7, ({ int i=2; i+=5; }));
+  ASSERT(3, ({ int i=5; i-=2; i; }));
+  ASSERT(3, ({ int i=5; i-=2; }));
+  ASSERT(6, ({ int i=3; i*=2; i; }));
+  ASSERT(6, ({ int i=3; i*=2; }));
+  ASSERT(3, ({ int i=6; i/=2; i; }));
+  ASSERT(3, ({ int i=6; i/=2; }));
+
   printf("OK\n");
   return 0;
 }

tokenize.c

@@ -115,7 +115,9 @@ static int from_hex(char c) {
 
 // Read a punctuator token from p and returns its length.
 static int read_punct(char *p) {
-  static char *kw[] = {"==", "!=", "<=", ">=", "->"};
+  static char *kw[] = {
+    "==", "!=", "<=", ">=", "->", "+=", "-=", "*=", "/=",
+  };
 
   for (int i = 0; i < sizeof(kw) / sizeof(*kw); i++)
     if (startswith(p, kw[i]))