Make HJSArrayLength more likely to have identical GVNs.

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index 47a9da3b45deb917e7b4a5c213b4db57a3625d1d..d07c1d5135a60222b53a4c46339149c7ae24a696 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -1929,19 +1929,10 @@ class HCallRuntime: public HCall<1> {
 
 class HJSArrayLength: public HTemplateInstruction<2> {
  public:
-  HJSArrayLength(HValue* value, HValue* typecheck,
-                 HType type = HType::Tagged()) {
-    set_type(type);
-    // The length of an array is stored as a tagged value in the array
-    // object. It is guaranteed to be 32 bit integer, but it can be
-    // represented as either a smi or heap number.
-    SetOperandAt(0, value);
-    SetOperandAt(1, typecheck);
-    set_representation(Representation::Tagged());
-    SetFlag(kUseGVN);
-    SetGVNFlag(kDependsOnArrayLengths);
-    SetGVNFlag(kDependsOnMaps);
-  }
+  static HJSArrayLength* Create(HGraph* graph,
+                                HValue* value,
+                                HValue* typecheck,
+                                HType type = HType::Tagged());
 
   virtual Representation RequiredInputRepresentation(int index) {
     return Representation::Tagged();
@@ -1949,6 +1940,7 @@ class HJSArrayLength: public HTemplateInstruction<2> {
 
   virtual void PrintDataTo(StringStream* stream);
 
+  const HValue* value() const { return OperandAt(0); }
   HValue* value() { return OperandAt(0); }
   HValue* typecheck() { return OperandAt(1); }
 
@@ -1959,6 +1951,20 @@ class HJSArrayLength: public HTemplateInstruction<2> {
 
  private:
   virtual bool IsDeletable() const { return true; }
+
+  HJSArrayLength(HValue* value, HValue* typecheck,
+                 HType type = HType::Tagged()) {
+    set_type(type);
+    // The length of an array is stored as a tagged value in the array
+    // object. It is guaranteed to be 32 bit integer, but it can be
+    // represented as either a smi or heap number.
+    SetOperandAt(0, value);
+    SetOperandAt(1, typecheck);
+    set_representation(Representation::Tagged());
+    SetFlag(kUseGVN);
+    SetGVNFlag(kDependsOnArrayLengths);
+    SetGVNFlag(kDependsOnMaps);
+  }
 };
 
 
@@ -2261,6 +2267,7 @@ class HCheckMaps: public HTemplateInstruction<2> {
 
   HValue* value() { return OperandAt(0); }
   SmallMapList* map_set() { return &map_set_; }
+  bool has_dependency() { return OperandAt(1) != OperandAt(0); }
 
   DECLARE_CONCRETE_INSTRUCTION(CheckMaps)