Remove redundant ids from AST

src/ast.cc

Index: src/ast.cc
diff --git a/src/ast.cc b/src/ast.cc
index ab9050daa0eee24e0e78d021e7e46c9b6b062b7f..327497c2d0b5c4e1d85fd7867a09eecd01ad096d 100644
--- a/src/ast.cc
+++ b/src/ast.cc
@@ -105,9 +105,14 @@ Assignment::Assignment(Zone* zone, Token::Value op, Expression* target,
       target_(target),
       value_(value),
       binary_operation_(NULL),
-      assignment_id_(id_gen->GetNextId()),
       is_uninitialized_(false),
-      store_mode_(STANDARD_STORE) {}
+      store_mode_(STANDARD_STORE) {
+#ifdef DEBUG
+    int assignment_id =
+#endif
+    id_gen->GetNextId();  // reserve assignment id
+    DCHECK(assignment_id == id().ToInt() + 2);
+  }
 
 
 Token::Value Assignment::binary_op() const {
@@ -992,10 +997,13 @@ CaseClause::CaseClause(Zone* zone, Expression* label,
     : Expression(zone, pos, id_gen),
       label_(label),
       statements_(statements),
-      compare_type_(Type::None(zone)),
-      compare_id_(id_gen->GetNextId()),
-      entry_id_(id_gen->GetNextId()) {}
-
+      compare_type_(Type::None(zone)) {
+#ifdef DEBUG
+    int compare_id =
+#endif
+    id_gen->ReserveIdRange(2);  // Reserve compare and entry ids
+    DCHECK(compare_id == id().ToInt() + 2);
+  }
 
 #define REGULAR_NODE(NodeType) \
   void AstConstructionVisitor::Visit##NodeType(NodeType* node) { \