[GNU] Support labels-as-values

chibicc.h

@@ -209,7 +209,9 @@ typedef enum {
   ND_CASE,      // "case"
   ND_BLOCK,     // { ... }
   ND_GOTO,      // "goto"
+  ND_GOTO_EXPR, // "goto" labels-as-values
   ND_LABEL,     // Labeled statement
+  ND_LABEL_VAL, // [GNU] Labels-as-values
   ND_FUNCALL,   // Function call
   ND_EXPR_STMT, // Expression statement
   ND_STMT_EXPR, // Statement expression
@@ -254,7 +256,7 @@ struct Node {
   bool pass_by_stack;
   Obj *ret_buffer;
 
-  // Goto or labeled statement
+  // Goto or labeled statement, or labels-as-values
   char *label;
   char *unique_label;
   Node *goto_next;

codegen.c

@@ -925,6 +925,9 @@ static void gen_expr(Node *node) {
 
     return;
   }
+  case ND_LABEL_VAL:
+    println("  lea %s(%%rip), %%rax", node->unique_label);
+    return;
   }
 
   switch (node->lhs->ty->kind) {
@@ -1194,6 +1197,10 @@ static void gen_stmt(Node *node) {
   case ND_GOTO:
     println("  jmp %s", node->unique_label);
     return;
+  case ND_GOTO_EXPR:
+    gen_expr(node->lhs);
+    println("  jmp *%%rax");
+    return;
   case ND_LABEL:
     println("%s:", node->unique_label);
     gen_stmt(node->lhs);

parse.c

@@ -1533,7 +1533,7 @@ static Node *asm_stmt(Token **rest, Token *tok) {
 //      | "while" "(" expr ")" stmt
 //      | "do" stmt "while" "(" expr ")" ";"
 //      | "asm" asm-stmt
-//      | "goto" ident ";"
+//      | "goto" (ident | "*" expr) ";"
 //      | "break" ";"
 //      | "continue" ";"
 //      | ident ":" stmt
@@ -1704,6 +1704,14 @@ static Node *stmt(Token **rest, Token *tok) {
     return asm_stmt(rest, tok);
 
   if (equal(tok, "goto")) {
+    if (equal(tok->next, "*")) {
+      // [GNU] `goto *ptr` jumps to the address specified by `ptr`.
+      Node *node = new_node(ND_GOTO_EXPR, tok);
+      node->lhs = expr(&tok, tok->next->next);
+      *rest = skip(tok, ";");
+      return node;
+    }
+
     Node *node = new_node(ND_GOTO, tok);
     node->label = get_ident(tok->next);
     node->goto_next = gotos;
@@ -2406,6 +2414,7 @@ static Node *cast(Token **rest, Token *tok) {
 
 // unary = ("+" | "-" | "*" | "&" | "!" | "~") cast
 //       | ("++" | "--") unary
+//       | "&&" ident
 //       | postfix
 static Node *unary(Token **rest, Token *tok) {
   if (equal(tok, "+"))
@@ -2448,6 +2457,16 @@ static Node *unary(Token **rest, Token *tok) {
   if (equal(tok, "--"))
     return to_assign(new_sub(unary(rest, tok->next), new_num(1, tok), tok));
 
+  // [GNU] labels-as-values
+  if (equal(tok, "&&")) {
+    Node *node = new_node(ND_LABEL_VAL, tok);
+    node->label = get_ident(tok->next);
+    node->goto_next = gotos;
+    gotos = node;
+    *rest = tok->next->next;
+    return node;
+  }
+
   return postfix(rest, tok);
 }
 
@@ -3005,7 +3024,7 @@ static void create_param_lvars(Type *param) {
   }
 }
 
-// This function matches gotos with labels.
+// This function matches gotos or labels-as-values with labels.
 //
 // We cannot resolve gotos as we parse a function because gotos
 // can refer a label that appears later in the function.

test/control.c

@@ -87,6 +87,10 @@ int main() {
   ASSERT(1, ({ int i=0; switch(7) { case 0 ... 7: i=1; break; case 8 ... 10: i=2; break; } i; }));
   ASSERT(1, ({ int i=0; switch(7) { case 0: i=1; break; case 7 ... 7: i=1; break; } i; }));
 
+  ASSERT(3, ({ void *p = &&v11; int i=0; goto *p; v11:i++; v12:i++; v13:i++; i; }));
+  ASSERT(2, ({ void *p = &&v22; int i=0; goto *p; v21:i++; v22:i++; v23:i++; i; }));
+  ASSERT(1, ({ void *p = &&v33; int i=0; goto *p; v31:i++; v32:i++; v33:i++; i; }));
+
   printf("OK\n");
   return 0;
 }

type.c

@@ -284,5 +284,8 @@ void add_type(Node *node) {
     }
     error_tok(node->tok, "statement expression returning void is not supported");
     return;
+  case ND_LABEL_VAL:
+    node->ty = pointer_to(ty_void);
+    return;
   }
 }