Don't use one-bit bit fields for enums -- they misbehave and are inefficient in VC++

src/hydrogen-instructions.h

 // 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.
 
 #ifndef V8_HYDROGEN_INSTRUCTIONS_H_
 #define V8_HYDROGEN_INSTRUCTIONS_H_
 
 #include <iosfwd>
 
 #include "src/v8.h"
@@ skipping 6788 matching lines @@
     SetOperandAt(2, context);
     SetAllSideEffects();
   }
 
   Handle<TypeFeedbackVector> feedback_vector_;
   FeedbackVectorICSlot slot_;
 };
 
 
 // Indicates whether the store is a store to an entry that was previously
-// initialized or not.
-enum StoreFieldOrKeyedMode {
+// initialized or not. Force this enum into an unsigned char to make it
+// take less space.
+enum StoreFieldOrKeyedMode : unsigned char {
   // The entry could be either previously initialized or not.
   INITIALIZING_STORE,
   // At the time of this store it is guaranteed that the entry is already
   // initialized.
   STORE_TO_INITIALIZED_ENTRY
 };
 
 
 class HStoreNamedField FINAL : public HTemplateInstruction<3> {
  public:
@@ skipping 128 matching lines @@
     DCHECK(!access.IsInobject() || access.existing_inobject_property() ||
            obj->IsAllocate() || obj->IsInnerAllocatedObject());
     SetOperandAt(0, obj);
     SetOperandAt(1, val);
     SetOperandAt(2, obj);
     access.SetGVNFlags(this, STORE);
   }
 
   HObjectAccess access_;
   HValue* dominator_;
-  bool has_transition_ : 1;
-  StoreFieldOrKeyedMode store_mode_ : 1;
+  bool has_transition_;
+  StoreFieldOrKeyedMode store_mode_;
 };
 
 
 class HStoreNamedGeneric FINAL : public HTemplateInstruction<3> {
  public:
   DECLARE_INSTRUCTION_WITH_CONTEXT_FACTORY_P4(HStoreNamedGeneric, HValue*,
                                               Handle<String>, HValue*,
                                               StrictMode);
   HValue* object() const { return OperandAt(0); }
   HValue* value() const { return OperandAt(1); }
@@ skipping 192 matching lines @@
     if ((elements_kind >= EXTERNAL_INT8_ELEMENTS &&
         elements_kind <= EXTERNAL_UINT32_ELEMENTS) ||
         (elements_kind >= UINT8_ELEMENTS &&
         elements_kind <= INT32_ELEMENTS)) {
       SetFlag(kTruncatingToInt32);
     }
   }
 
   ElementsKind elements_kind_;
   uint32_t base_offset_;
-  bool is_dehoisted_ : 1;
-  bool is_uninitialized_ : 1;
-  StoreFieldOrKeyedMode store_mode_: 1;
+  bool is_dehoisted_;
+  bool is_uninitialized_;
+  StoreFieldOrKeyedMode store_mode_;
   HValue* dominator_;
 };
 
 
 class HStoreKeyedGeneric FINAL : public HTemplateInstruction<4> {
  public:
   DECLARE_INSTRUCTION_WITH_CONTEXT_FACTORY_P4(HStoreKeyedGeneric, HValue*,
                                               HValue*, HValue*, StrictMode);
 
   HValue* object() const { return OperandAt(0); }
@@ skipping 725 matching lines @@
 };
 
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_