[ast] Mark removed scopes as such.

src/ast/scopes.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/ast/scopes.h"
 
 #include <set>
 
 #include "src/accessors.h"
 #include "src/ast/ast.h"
@@ skipping 618 matching lines @@
       new (zone()) Variable(this, name, CONST, kind, kCreatedInitialized);
   if (calls_sloppy_eval()) {
     NonLocal(name, DYNAMIC);
   } else {
     variables_.Add(zone(), function_);
   }
   return function_;
 }
 
 bool Scope::HasBeenRemoved() const {
-  // TODO(neis): Store this information somewhere instead of calculating it.
-
-  if (!is_block_scope()) return false;  // Shortcut.
-
-  Scope* parent = outer_scope();
-  if (parent == nullptr) {
-    DCHECK(is_script_scope());
-    return false;
+  if (sibling() == this) {
+    DCHECK_NULL(inner_scope_);
+    DCHECK(is_block_scope());
+    return true;
   }
-
-  Scope* sibling = parent->inner_scope();
-  for (; sibling != nullptr; sibling = sibling->sibling()) {
-    if (sibling == this) return false;
-  }
-
-  DCHECK_NULL(inner_scope_);
-  return true;
+  return false;
 }
 
 Scope* Scope::GetUnremovedScope() {
   Scope* scope = this;
   while (scope != nullptr && scope->HasBeenRemoved()) {
     scope = scope->outer_scope();
   }
   DCHECK_NOT_NULL(scope);
   return scope;
 }
 
 Scope* Scope::FinalizeBlockScope() {
   DCHECK(is_block_scope());
+  DCHECK(!HasBeenRemoved());
 
   if (variables_.occupancy() > 0 ||
       (is_declaration_scope() && calls_sloppy_eval())) {
     return this;
   }
 
   // Remove this scope from outer scope.
   outer_scope()->RemoveInnerScope(this);
 
   // Reparent inner scopes.
@@ skipping 18 matching lines @@
       }
       unresolved->set_next_unresolved(outer_scope()->unresolved_);
     }
     outer_scope()->unresolved_ = unresolved_;
     unresolved_ = nullptr;
   }
 
   PropagateUsageFlagsToScope(outer_scope_);
   // This block does not need a context.
   num_heap_slots_ = 0;
-  return NULL;
+
+  // Mark scope as removed by making it its own sibling.
+  sibling_ = this;
+  DCHECK(HasBeenRemoved());
+
+  return nullptr;
 }
 
 void DeclarationScope::AddLocal(Variable* var) {
   DCHECK(!already_resolved_);
   // Temporaries are only placed in ClosureScopes.
   DCHECK_EQ(GetClosureScope(), this);
   locals_.Add(var);
 }
 
 Variable* Scope::Declare(Zone* zone, const AstRawString* name,
@@ skipping 1353 matching lines @@
   Variable* function =
       is_function_scope() ? AsDeclarationScope()->function_var() : nullptr;
   bool is_function_var_in_context =
       function != nullptr && function->IsContextSlot();
   return num_heap_slots() - Context::MIN_CONTEXT_SLOTS -
          (is_function_var_in_context ? 1 : 0);
 }
 
 }  // namespace internal
 }  // namespace v8