Make the performance of the VM more predictable by not letting the hash seed

src/scopes.cc

Index: src/scopes.cc
===================================================================
--- src/scopes.cc	(revision 12363)
+++ src/scopes.cc	(working copy)
@@ -594,6 +594,21 @@
 }
 
 
+class VarAndOrder {
+ public:
+  VarAndOrder(Variable* var, int order) : var_(var), order_(order) { }
+  Variable* var() const { return var_; }
+  int order() const { return order_; }
+  static int Compare(const VarAndOrder* a, const VarAndOrder* b) {
+    return a->order_ - b->order_;
+  }
+
+ private:
+  Variable* var_;
+  int order_;
+};
+
+
 void Scope::CollectStackAndContextLocals(ZoneList<Variable*>* stack_locals,
                                          ZoneList<Variable*>* context_locals) {
   ASSERT(stack_locals != NULL);
@@ -608,19 +623,27 @@
     }
   }
 
+  ZoneList<VarAndOrder> vars(variables_.occupancy(), zone());
+
   // Collect declared local variables.
   for (VariableMap::Entry* p = variables_.Start();
        p != NULL;
        p = variables_.Next(p)) {
     Variable* var = reinterpret_cast<Variable*>(p->value);
     if (var->is_used()) {
-      if (var->IsStackLocal()) {
-        stack_locals->Add(var, zone());
-      } else if (var->IsContextSlot()) {
-        context_locals->Add(var, zone());
-      }
+      vars.Add(VarAndOrder(var, p->order), zone());
     }
   }
+  vars.Sort(VarAndOrder::Compare);
+  int var_count = vars.length();
+  for (int i = 0; i < var_count; i++) {
+    Variable* var = vars[i].var();
+    if (var->IsStackLocal()) {
+      stack_locals->Add(var, zone());
+    } else if (var->IsContextSlot()) {
+      context_locals->Add(var, zone());
+    }
+  }
 }
 
 
@@ -1256,13 +1279,21 @@
     AllocateNonParameterLocal(temps_[i]);
   }
 
+  ZoneList<VarAndOrder> vars(variables_.occupancy(), zone());
+
   for (VariableMap::Entry* p = variables_.Start();
        p != NULL;
        p = variables_.Next(p)) {
     Variable* var = reinterpret_cast<Variable*>(p->value);
-    AllocateNonParameterLocal(var);
+    vars.Add(VarAndOrder(var, p->order), zone());
   }
 
+  vars.Sort(VarAndOrder::Compare);
+  int var_count = vars.length();
+  for (int i = 0; i < var_count; i++) {
+    AllocateNonParameterLocal(vars[i].var());
+  }
+
   // For now, function_ must be allocated at the very end.  If it gets
   // allocated in the context, it must be the last slot in the context,
   // because of the current ScopeInfo implementation (see