Merge 6168:6800 from bleeding_edge to experimental/gc branch.

include/v8.h

Index: include/v8.h
===================================================================
--- include/v8.h	(revision 6800)
+++ include/v8.h	(working copy)
@@ -462,7 +462,6 @@
 
   void Leave();
 
-
   internal::Object** prev_next_;
   internal::Object** prev_limit_;
 
@@ -2515,6 +2514,7 @@
   size_t total_heap_size() { return total_heap_size_; }
   size_t total_heap_size_executable() { return total_heap_size_executable_; }
   size_t used_heap_size() { return used_heap_size_; }
+  size_t heap_size_limit() { return heap_size_limit_; }
 
  private:
   void set_total_heap_size(size_t size) { total_heap_size_ = size; }
@@ -2522,10 +2522,12 @@
     total_heap_size_executable_ = size;
   }
   void set_used_heap_size(size_t size) { used_heap_size_ = size; }
+  void set_heap_size_limit(size_t size) { heap_size_limit_ = size; }
 
   size_t total_heap_size_;
   size_t total_heap_size_executable_;
   size_t used_heap_size_;
+  size_t heap_size_limit_;
 
   friend class V8;
 };
@@ -3050,7 +3052,22 @@
  */
 class V8EXPORT Context {
  public:
-  /** Returns the global object of the context. */
+  /**
+   * Returns the global proxy object or global object itself for
+   * detached contexts.
+   *
+   * Global proxy object is a thin wrapper whose prototype points to
+   * actual context's global object with the properties like Object, etc.
+   * This is done that way for security reasons (for more details see
+   * https://wiki.mozilla.org/Gecko:SplitWindow).
+   *
+   * Please note that changes to global proxy object prototype most probably
+   * would break VM---v8 expects only global object as a prototype of
+   * global proxy object.
+   *
+   * If DetachGlobal() has been invoked, Global() would return actual global
+   * object until global is reattached with ReattachGlobal().
+   */
   Local<Object> Global();
 
   /**
@@ -3350,10 +3367,10 @@
 const int kSmiTagSize = 1;
 const intptr_t kSmiTagMask = (1 << kSmiTagSize) - 1;
 
-template <size_t ptr_size> struct SmiConstants;
+template <size_t ptr_size> struct SmiTagging;
 
 // Smi constants for 32-bit systems.
-template <> struct SmiConstants<4> {
+template <> struct SmiTagging<4> {
   static const int kSmiShiftSize = 0;
   static const int kSmiValueSize = 31;
   static inline int SmiToInt(internal::Object* value) {
@@ -3361,10 +3378,15 @@
     // Throw away top 32 bits and shift down (requires >> to be sign extending).
     return static_cast<int>(reinterpret_cast<intptr_t>(value)) >> shift_bits;
   }
+
+  // For 32-bit systems any 2 bytes aligned pointer can be encoded as smi
+  // with a plain reinterpret_cast.
+  static const uintptr_t kEncodablePointerMask = 0x1;
+  static const int kPointerToSmiShift = 0;
 };
 
 // Smi constants for 64-bit systems.
-template <> struct SmiConstants<8> {
+template <> struct SmiTagging<8> {
   static const int kSmiShiftSize = 31;
   static const int kSmiValueSize = 32;
   static inline int SmiToInt(internal::Object* value) {
@@ -3372,10 +3394,26 @@
     // Shift down and throw away top 32 bits.
     return static_cast<int>(reinterpret_cast<intptr_t>(value) >> shift_bits);
   }
+
+  // To maximize the range of pointers that can be encoded
+  // in the available 32 bits, we require them to be 8 bytes aligned.
+  // This gives 2 ^ (32 + 3) = 32G address space covered.
+  // It might be not enough to cover stack allocated objects on some platforms.
+  static const int kPointerAlignment = 3;
+
+  static const uintptr_t kEncodablePointerMask =
+      ~(uintptr_t(0xffffffff) << kPointerAlignment);
+
+  static const int kPointerToSmiShift =
+      kSmiTagSize + kSmiShiftSize - kPointerAlignment;
 };
 
-const int kSmiShiftSize = SmiConstants<kApiPointerSize>::kSmiShiftSize;
-const int kSmiValueSize = SmiConstants<kApiPointerSize>::kSmiValueSize;
+typedef SmiTagging<kApiPointerSize> PlatformSmiTagging;
+const int kSmiShiftSize = PlatformSmiTagging::kSmiShiftSize;
+const int kSmiValueSize = PlatformSmiTagging::kSmiValueSize;
+const uintptr_t kEncodablePointerMask =
+    PlatformSmiTagging::kEncodablePointerMask;
+const int kPointerToSmiShift = PlatformSmiTagging::kPointerToSmiShift;
 
 template <size_t ptr_size> struct InternalConstants;
 
@@ -3409,7 +3447,7 @@
   static const int kFullStringRepresentationMask = 0x07;
   static const int kExternalTwoByteRepresentationTag = 0x02;
 
-  static const int kJSObjectType = 0x9f;
+  static const int kJSObjectType = 0xa0;
   static const int kFirstNonstringType = 0x80;
   static const int kProxyType = 0x85;
 
@@ -3423,7 +3461,7 @@
   }
 
   static inline int SmiValue(internal::Object* value) {
-    return SmiConstants<kApiPointerSize>::SmiToInt(value);
+    return PlatformSmiTagging::SmiToInt(value);
   }
 
   static inline int GetInstanceType(internal::Object* obj) {
@@ -3432,9 +3470,14 @@
     return ReadField<uint8_t>(map, kMapInstanceTypeOffset);
   }
 
+  static inline void* GetExternalPointerFromSmi(internal::Object* value) {
+    const uintptr_t address = reinterpret_cast<uintptr_t>(value);
+    return reinterpret_cast<void*>(address >> kPointerToSmiShift);
+  }
+
   static inline void* GetExternalPointer(internal::Object* obj) {
     if (HasSmiTag(obj)) {
-      return obj;
+      return GetExternalPointerFromSmi(obj);
     } else if (GetInstanceType(obj) == kProxyType) {
       return ReadField<void*>(obj, kProxyProxyOffset);
     } else {