Change heuristics for deciding phi-representation types to use int32 more frequently.

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
===================================================================
--- src/hydrogen-instructions.h	(revision 7737)
+++ src/hydrogen-instructions.h	(working copy)
@@ -554,6 +554,8 @@
     representation_ = r;
   }
 
+  virtual bool IsConvertibleToInteger() const { return true; }
+
   HType type() const { return type_; }
   void set_type(HType type) {
     ASSERT(HasNoUses());
@@ -1922,7 +1924,8 @@
       : inputs_(2),
         merged_index_(merged_index),
         phi_id_(-1),
-        is_live_(false) {
+        is_live_(false),
+        is_convertible_to_integer_(true) {
     for (int i = 0; i < Representation::kNumRepresentations; i++) {
       non_phi_uses_[i] = 0;
       indirect_uses_[i] = 0;
@@ -2000,6 +2003,14 @@
   }
   virtual Opcode opcode() const { return HValue::kPhi; }
 
+  virtual bool IsConvertibleToInteger() const {
+    return is_convertible_to_integer_;
+  }
+
+  void set_is_convertible_to_integer(bool b) {
+    is_convertible_to_integer_ = b;
+  }
+
  protected:
   virtual void DeleteFromGraph();
   virtual void InternalSetOperandAt(int index, HValue* value) {
@@ -2014,6 +2025,7 @@
   int indirect_uses_[Representation::kNumRepresentations];
   int phi_id_;
   bool is_live_;
+  bool is_convertible_to_integer_;
 };
 
 
@@ -2044,6 +2056,14 @@
     return Representation::None();
   }
 
+  virtual bool IsConvertibleToInteger() const {
+    if (handle_->IsSmi()) return true;
+    if (handle_->IsHeapNumber() &&
+        (HeapNumber::cast(*handle_)->value() ==
+         static_cast<double>(NumberToInt32(*handle_)))) return true;
+    return false;
+  }
+
   virtual bool EmitAtUses() { return !representation().IsDouble(); }
   virtual void PrintDataTo(StringStream* stream);
   virtual HType CalculateInferredType();