Better pack fields in Variable

src/globals.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_GLOBALS_H_
 #define V8_GLOBALS_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 860 matching lines @@
 
 const uint64_t kHoleNanInt64 =
     (static_cast<uint64_t>(kHoleNanUpper32) << 32) | kHoleNanLower32;
 
 
 // ES6 section 20.1.2.6 Number.MAX_SAFE_INTEGER
 const double kMaxSafeInteger = 9007199254740991.0;  // 2^53-1
 
 
 // The order of this enum has to be kept in sync with the predicates below.
-enum VariableMode {
+enum VariableMode : uint8_t {
   // User declared variables:
   VAR,  // declared via 'var', and 'function' declarations
 
   CONST_LEGACY,  // declared via legacy 'const' declarations
 
   LET,  // declared via 'let' declarations (first lexical)
 
   CONST,  // declared via 'const' declarations (last lexical)
 
   // Variables introduced by the compiler:
   TEMPORARY,  // temporary variables (not user-visible), stack-allocated
               // unless the scope as a whole has forced context allocation
 
   DYNAMIC,  // always require dynamic lookup (we don't know
             // the declaration)
 
   DYNAMIC_GLOBAL,  // requires dynamic lookup, but we know that the
                    // variable is global unless it has been shadowed
                    // by an eval-introduced variable
 
-  DYNAMIC_LOCAL  // requires dynamic lookup, but we know that the
-                 // variable is local and where it is unless it
-                 // has been shadowed by an eval-introduced
-                 // variable
+  DYNAMIC_LOCAL,  // requires dynamic lookup, but we know that the
+                  // variable is local and where it is unless it
+                  // has been shadowed by an eval-introduced
+                  // variable
+
+  kLastVariableMode = DYNAMIC_LOCAL
 };
 
 inline bool IsDynamicVariableMode(VariableMode mode) {
   return mode >= DYNAMIC && mode <= DYNAMIC_LOCAL;
 }
 
 
 inline bool IsDeclaredVariableMode(VariableMode mode) {
   return mode >= VAR && mode <= CONST;
 }
 
 
 inline bool IsLexicalVariableMode(VariableMode mode) {
   return mode >= LET && mode <= CONST;
 }
 
 
 inline bool IsImmutableVariableMode(VariableMode mode) {
   return mode == CONST || mode == CONST_LEGACY;
 }
 
-enum class VariableLocation {
+enum class VariableLocation : uint8_t {
   // Before and during variable allocation, a variable whose location is
   // not yet determined.  After allocation, a variable looked up as a
   // property on the global object (and possibly absent).  name() is the
   // variable name, index() is invalid.
   UNALLOCATED,
 
   // A slot in the parameter section on the stack.  index() is the
   // parameter index, counting left-to-right.  The receiver is index -1;
   // the first parameter is index 0.
   PARAMETER,
@@ skipping 12 matching lines @@
   // index in the context object on the heap, starting at 0.  scope() is the
   // corresponding script scope.
   GLOBAL,
 
   // A named slot in a heap context.  name() is the variable name in the
   // context object on the heap, with lookup starting at the current
   // context.  index() is invalid.
   LOOKUP,
 
   // A named slot in a module's export table.
-  MODULE
+  MODULE,
+
+  kLastVariableLocation = MODULE
 };
 
 // ES6 Draft Rev3 10.2 specifies declarative environment records with mutable
 // and immutable bindings that can be in two states: initialized and
 // uninitialized. In ES5 only immutable bindings have these two states. When
 // accessing a binding, it needs to be checked for initialization. However in
 // the following cases the binding is initialized immediately after creation
 // so the initialization check can always be skipped:
 // 1. Var declared local variables.
 //      var foo;
@@ skipping 13 matching lines @@
 // properties of some object. In the specification only mutable bindings exist
 // (which may be non-writable) and have no distinct initialization step. However
 // V8 allows const declarations in global code with distinct creation and
 // initialization steps which are represented by non-writable properties in the
 // global object. As a result also these bindings need to be checked for
 // initialization.
 //
 // The following enum specifies a flag that indicates if the binding needs a
 // distinct initialization step (kNeedsInitialization) or if the binding is
 // immediately initialized upon creation (kCreatedInitialized).
-enum InitializationFlag {
-  kNeedsInitialization,
-  kCreatedInitialized
-};
+enum InitializationFlag : uint8_t { kNeedsInitialization, kCreatedInitialized };
 
-
-enum MaybeAssignedFlag { kNotAssigned, kMaybeAssigned };
-
+enum MaybeAssignedFlag : uint8_t { kNotAssigned, kMaybeAssigned };
 
 // Serialized in PreparseData, so numeric values should not be changed.
 enum ParseErrorType { kSyntaxError = 0, kReferenceError = 1 };
 
 
 enum MinusZeroMode {
   TREAT_MINUS_ZERO_AS_ZERO,
   FAIL_ON_MINUS_ZERO
 };
 
@@ skipping 144 matching lines @@
  public:
   enum { kNone = 0x00, kSignedSmall = 0x01, kNumber = 0x3, kAny = 0x7 };
 };
 
 }  // namespace internal
 }  // namespace v8
 
 namespace i = v8::internal;
 
 #endif  // V8_GLOBALS_H_