Heap::gc_count_, last_gc_count, and kGCsBetweenCleanup should be unsigned

in order to not be vulnerable to overflow issues.

Patch by Mark Lam of Hewlett-Packard Development Company, LP

Review URL: http://codereview.chromium.org/5966001

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6870 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/heap.cc

@@ -134,7 +134,7 @@ Heap::HeapState Heap::gc_state_ = NOT_IN_GC;
 
 int Heap::mc_count_ = 0;
 int Heap::ms_count_ = 0;
-int Heap::gc_count_ = 0;
+unsigned int Heap::gc_count_ = 0;
 
 GCTracer* Heap::tracer_ = NULL;
 
@@ -3796,9 +3796,9 @@ bool Heap::IdleNotification() {
   static const int kIdlesBeforeMarkSweep = 7;
   static const int kIdlesBeforeMarkCompact = 8;
   static const int kMaxIdleCount = kIdlesBeforeMarkCompact + 1;
-  static const int kGCsBetweenCleanup = 4;
+  static const unsigned int kGCsBetweenCleanup = 4;
   static int number_idle_notifications = 0;
-  static int last_gc_count = gc_count_;
+  static unsigned int last_gc_count = gc_count_;
 
   bool uncommit = true;
   bool finished = false;
@@ -3807,7 +3807,7 @@ bool Heap::IdleNotification() {
   // GCs have taken place. This allows another round of cleanup based
   // on idle notifications if enough work has been carried out to
   // provoke a number of garbage collections.
-  if (gc_count_ < last_gc_count + kGCsBetweenCleanup) {
+  if (gc_count_ - last_gc_count < kGCsBetweenCleanup) {
     number_idle_notifications =
         Min(number_idle_notifications + 1, kMaxIdleCount);
   } else {

src/heap.h

@@ -1180,7 +1180,7 @@ class Heap : public AllStatic {
 
   static int mc_count_;  // how many mark-compact collections happened
   static int ms_count_;  // how many mark-sweep collections happened
-  static int gc_count_;  // how many gc happened
+  static unsigned int gc_count_;  // how many gc happened
 
   // Total length of the strings we failed to flatten since the last GC.
   static int unflattened_strings_length_;
@@ -1907,7 +1907,7 @@ class GCTracer BASE_EMBEDDED {
   void set_collector(GarbageCollector collector) { collector_ = collector; }
 
   // Sets the GC count.
-  void set_gc_count(int count) { gc_count_ = count; }
+  void set_gc_count(unsigned int count) { gc_count_ = count; }
 
   // Sets the full GC count.
   void set_full_gc_count(int count) { full_gc_count_ = count; }
@@ -1950,7 +1950,7 @@ class GCTracer BASE_EMBEDDED {
 
   // A count (including this one, eg, the first collection is 1) of the
   // number of garbage collections.
-  int gc_count_;
+  unsigned int gc_count_;
 
   // A count (including this one) of the number of full garbage collections.
   int full_gc_count_;