feat: support constant expression

parse.c

@@ -160,6 +160,7 @@ Node *declaration();
 bool is_typename();
 Node *stmt();
 Node *expr();
+long const_expr();
 Node *assign();
 Node *conditional();
 Node *bitand();
@@ -353,7 +354,7 @@ Type *abstract_declarator(Type *ty) {
   return type_suffix(ty);
 }
 
-// type-suffix = ("[" num? "]" type-suffix)?
+// type-suffix = ("[" const-expr? "]" type-suffix)?
 Type *type_suffix(Type *ty) {
   if (!consume("[")) {
     return ty;
@@ -362,7 +363,7 @@ Type *type_suffix(Type *ty) {
   int sz = 0;
   bool is_incomplete = true;
   if (!consume("]")) {
-    sz = expect_number();
+    sz = const_expr();
     is_incomplete = false;
     expect("]");
   }
@@ -460,7 +461,8 @@ Type *struct_decl() {
 
 // enum-specifier = "enum" ident
 //                | "enum" ident? "{" enum-list? "}"
-// enum-list = ident ("=" num)? ("," ident ("=" num)?)* ","?
+// enum-list = enum-elem ("," enum-elem)* ","?
+// enum-elem = ident ("=" const-expr)?
 Type *enum_specifier() {
   expect("enum");
   Type *ty = enum_type();
@@ -485,7 +487,7 @@ Type *enum_specifier() {
   for (;;) {
     char *name = expect_ident();
     if (consume("=")) {
-      count = expect_number();
+      count = const_expr();
     }
     VarScope *sc = push_scope(name);
     sc->enum_ty = ty;
@@ -669,7 +671,7 @@ bool is_typename() {
 // stmt = "return" expr ";"
 //      | "if" "(" expr ")" stmt ("else" stmt)?
 //      | "switch" "(" expr ")" stmt
-//      | "case" num ":" stmt
+//      | "case" const-expr ":" stmt
 //      | "default" ":" stmt
 //      | "while" "(" expr ")" stmt
 //      | "for" "(" (expr? ";" | declaration) expr? ";" expr? ")" stmt
@@ -776,7 +778,7 @@ Node *stmt() {
     if (!current_switch) {
       error_tok(tok, "stray case");
     }
-    int val = expect_number();
+    int val = const_expr();
     expect(":");
 
     Node *node = new_unary(ND_CASE, stmt(), tok);
@@ -821,6 +823,55 @@ Node *expr() {
   }
   return node;
 }
+
+long eval(Node *node) {
+  switch (node->kind) {
+    case ND_ADD:
+      return eval(node->lhs) + eval(node->rhs);
+    case ND_SUB:
+      return eval(node->lhs) - eval(node->rhs);
+    case ND_MUL:
+      return eval(node->lhs) * eval(node->rhs);
+    case ND_DIV:
+      return eval(node->lhs) / eval(node->rhs);
+    case ND_BITAND:
+      return eval(node->lhs) & eval(node->rhs);
+    case ND_BITOR:
+      return eval(node->lhs) | eval(node->rhs);
+    case ND_BITXOR:
+      return eval(node->lhs) | eval(node->rhs);
+    case ND_SHL:
+      return eval(node->lhs) << eval(node->rhs);
+    case ND_SHR:
+      return eval(node->lhs) >> eval(node->rhs);
+    case ND_EQ:
+      return eval(node->lhs) == eval(node->rhs);
+    case ND_NE:
+      return eval(node->lhs) != eval(node->rhs);
+    case ND_LT:
+      return eval(node->lhs) < eval(node->rhs);
+    case ND_LE:
+      return eval(node->lhs) <= eval(node->rhs);
+    case ND_TERNARY:
+      return eval(node->cond) ? eval(node->then) : eval(node->els);
+    case ND_COMMA:
+      return eval(node->rhs);
+    case ND_NOT:
+      return !eval(node->lhs);
+    case ND_BITNOT:
+      return ~eval(node->lhs);
+    case ND_LOGAND:
+      return eval(node->lhs) && eval(node->rhs);
+    case ND_LOGOR:
+      return eval(node->lhs) || eval(node->rhs);
+    case ND_NUM:
+      return node->val;
+  }
+  error_tok(node->tok, "not a constant expression");
+}
+
+long const_expr() { return eval(conditional()); }
+
 // assign = conditional (assign-op assign)?
 // assign-op = "=" | "+=" | "-=" | "*=" | "/=" | "%=" | "<<=" | ">>="
 Node *assign() {

tests

@@ -828,6 +828,12 @@ int main() {
   assert(2, 0?1:2, "0?1:2");
   assert(1, 1?1:2, "0?1:2");
 
+  assert(10, ({ enum { ten=1+2+3+4, }; ten; }), "enum { ten=1+2+3+4, }; ten;");
+  assert(1, ({ int i=0; switch(3) { case 5-2+0*3: i++; } i; }), "int i=0; switch(3) { case 5-2+0*3: i++; ); i;");
+  assert(8, ({ int x[1+1]; sizeof(x); }), "int x[1+1]; sizeof(x);");
+  assert(2, ({ char x[1?2:3]; sizeof(x); }), "char x[0?2:3]; sizeof(x);");
+  assert(3, ({ char x[0?2:3]; sizeof(x); }), "char x[1?2:3]; sizeof(x);");
+
   printf("OK\n");
   return 0;
 }