Better pack fields in Variable

src/ast/variables.h

 // Copyright 2011 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.
 
 #ifndef V8_AST_VARIABLES_H_
 #define V8_AST_VARIABLES_H_
 
 #include "src/ast/ast-value-factory.h"
 #include "src/zone.h"
 
@@ skipping 31 matching lines @@
   // parameter initializers.
   void set_scope(Scope* scope) { scope_ = scope; }
 
   Handle<String> name() const { return name_->string(); }
   const AstRawString* raw_name() const { return name_; }
   VariableMode mode() const { return VariableModeField::decode(bit_field_); }
   bool has_forced_context_allocation() const {
     return ForceContextAllocationField::decode(bit_field_);
   }
   void ForceContextAllocation() {
+    DCHECK(IsUnallocated() || IsContextSlot());
     bit_field_ = ForceContextAllocationField::update(bit_field_, true);
   }
   bool is_used() { return IsUsedField::decode(bit_field_); }
   void set_is_used() { bit_field_ = IsUsedField::update(bit_field_, true); }
   MaybeAssignedFlag maybe_assigned() const {
     return MaybeAssignedFlagField::decode(bit_field_);
   }
   void set_maybe_assigned() {
     bit_field_ = MaybeAssignedFlagField::update(bit_field_, kMaybeAssigned);
   }
@@ skipping 79 matching lines @@
   class InitializationFlagField
       : public BitField16<InitializationFlag, IsUsedField::kNext, 2> {};
   class MaybeAssignedFlagField
       : public BitField16<MaybeAssignedFlag, InitializationFlagField::kNext,
                           2> {};
 };
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_AST_VARIABLES_H_