Bug 1246061.

js/public/HashTable.h

@@ -13,6 +13,7 @@
 #include "mozilla/Casting.h"
 #include "mozilla/MemoryReporting.h"
 #include "mozilla/Move.h"
+#include "mozilla/Opaque.h"
 #include "mozilla/PodOperations.h"
 #include "mozilla/ReentrancyGuard.h"
 #include "mozilla/TemplateLib.h"
@@ -32,6 +33,8 @@ namespace detail {
 
 /*****************************************************************************/
 
+using Generation = mozilla::Opaque<uint64_t>;
+
 // A JS-friendly, STL-like container providing a hash-based map from keys to
 // values. In particular, HashMap calls constructors and destructors of all
 // objects added so non-PODs may be used safely.
@@ -205,7 +208,9 @@ class HashMap
 
     // If |generation()| is the same before and after a HashMap operation,
     // pointers into the table remain valid.
-    uint32_t generation() const                       { return impl.generation(); }
+    Generation generation() const {
+        return impl.generation();
+    }
 
     /************************************************** Shorthand operations */
 
@@ -436,7 +441,9 @@ class HashSet
 
     // If |generation()| is the same before and after a HashSet operation,
     // pointers into the table remain valid.
-    uint32_t generation() const                       { return impl.generation(); }
+    Generation generation() const {
+        return impl.generation();
+    }
 
     /************************************************** Shorthand operations */
 
@@ -771,7 +778,7 @@ class HashTable : private AllocPolicy
         Entry* entry_;
 #ifdef JS_DEBUG
         const HashTable* table_;
-        uint32_t generation;
+        Generation generation;
 #endif
 
       protected:
@@ -878,7 +885,7 @@ class HashTable : private AllocPolicy
 #ifdef JS_DEBUG
         const HashTable* table_;
         uint64_t mutationCount;
-        uint32_t generation;
+        Generation generation;
         bool validEntry;
 #endif
 
@@ -1017,8 +1024,8 @@ class HashTable : private AllocPolicy
     static const size_t CAP_BITS = 24;
 
   public:
-    Entry*      table;                 // entry storage
-    uint32_t    gen;                    // entry storage generation number
+    uint64_t    gen;                    // entry storage generation number
+    Entry*      table;                  // entry storage
     uint32_t    entryCount;             // number of entries in table
     uint32_t    removedCount:CAP_BITS;  // removed entry sentinels in table
     uint32_t    hashShift:8;            // multiplicative hash shift
@@ -1102,8 +1109,8 @@ class HashTable : private AllocPolicy
   public:
     explicit HashTable(AllocPolicy ap)
       : AllocPolicy(ap)
-      , table(nullptr)
       , gen(0)
+      , table(nullptr)
       , entryCount(0)
       , removedCount(0)
       , hashShift(sHashBits)
@@ -1529,10 +1536,10 @@ class HashTable : private AllocPolicy
         return JS_BIT(sHashBits - hashShift);
     }
 
-    uint32_t generation() const
+    Generation generation() const
     {
         MOZ_ASSERT(table);
-        return gen;
+        return Generation(gen);
     }
 
     size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const

js/src/jsapi.h

@@ -275,10 +275,6 @@ class AutoHashMapRooter : protected AutoGCRooter
         return map.sizeOfIncludingThis(mallocSizeOf);
     }
 
-    uint32_t generation() const {
-        return map.generation();
-    }
-
     /************************************************** Shorthand operations */
 
     bool has(const Lookup& l) const {
@@ -390,10 +386,6 @@ class AutoHashSetRooter : protected AutoGCRooter
         return set.sizeOfIncludingThis(mallocSizeOf);
     }
 
-    uint32_t generation() const {
-        return set.generation();
-    }
-
     /************************************************** Shorthand operations */
 
     bool has(const Lookup& l) const {

js/src/jscntxt.h

@@ -35,11 +35,11 @@ typedef HashSet<Shape*> ShapeSet;
 /* Detects cycles when traversing an object graph. */
 class AutoCycleDetector
 {
+    Generation hashsetGenerationAtInit;
     JSContext* cx;
     RootedObject obj;
-    bool cyclic;
-    uint32_t hashsetGenerationAtInit;
     ObjectSet::AddPtr hashsetAddPointer;
+    bool cyclic;
     MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
 
   public:

js/src/jswatchpoint.cpp

@@ -27,15 +27,15 @@ namespace {
 
 class AutoEntryHolder {
     typedef WatchpointMap::Map Map;
+    Generation gen;
     Map& map;
     Map::Ptr p;
-    uint32_t gen;
     RootedObject obj;
     RootedId id;
 
   public:
     AutoEntryHolder(JSContext* cx, Map& map, Map::Ptr p)
-      : map(map), p(p), gen(map.generation()), obj(cx, p->key().object), id(cx, p->key().id)
+      : gen(map.generation()), map(map), p(p), obj(cx, p->key().object), id(cx, p->key().id)
     {
         MOZ_ASSERT(!p->value().held);
         p->value().held = true;

js/src/shell/jsheaptools.cpp

@@ -272,7 +272,7 @@ HeapReverser::traverseEdge(void* cell, JSGCTraceKind kind)
          * visited from the main loop.
          */
         Node n(kind);
-        uint32_t generation = map.generation();
+        Generation generation = map.generation();
         if (!map.add(a, cell, Move(n)) ||
             !work.append(Child(cell, kind)))
             return false;

mfbt/Opaque.h

@@ -0,0 +1,44 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* An opaque integral type supporting only comparison operators. */
+
+#ifndef mozilla_Opaque_h
+#define mozilla_Opaque_h
+
+#include "mozilla/TypeTraits.h"
+
+namespace mozilla {
+
+/**
+ * Opaque<T> is a replacement for integral T in cases where only comparisons
+ * must be supported, and it's desirable to prevent accidental dependency on
+ * exact values.
+ */
+template<typename T>
+class Opaque final
+{
+  static_assert(mozilla::IsIntegral<T>::value,
+                "mozilla::Opaque only supports integral types");
+
+  T mValue;
+
+public:
+  Opaque() {}
+  explicit Opaque(T aValue) : mValue(aValue) {}
+
+  bool operator==(const Opaque& aOther) const {
+    return mValue == aOther.mValue;
+  }
+
+  bool operator!=(const Opaque& aOther) const {
+    return !(*this == aOther);
+  }
+};
+
+} // namespace mozilla
+
+#endif /* mozilla_Opaque_h */

mfbt/moz.build

@@ -53,6 +53,7 @@ EXPORTS.mozilla = [
     'Move.h',
     'NullPtr.h',
     'NumericLimits.h',
+    'Opaque.h',
     'Pair.h',
     'PodOperations.h',
     'Poison.h',