Make HJSArrayLength more likely to have identical GVNs.

src/hydrogen.h

Index: src/hydrogen.h
diff --git a/src/hydrogen.h b/src/hydrogen.h
index 98b05d147a290d67e10cbe57daae8bc2f73b02ea..b2e3fa7f8c64457eb1d2a9c677ddf236e6f85996 100644
--- a/src/hydrogen.h
+++ b/src/hydrogen.h
@@ -370,6 +370,17 @@ class HGraph: public ZoneObject {
     uint32_instructions_->Add(instr, zone());
   }
 
+  // We record all HJSArrayLength instructions to process them later.
+  void RecordJSArrayLength(HJSArrayLength* inst) {
+    array_lengths_.Add(inst, zone());
+  }
+  // To make it likely that GVN will match two HJSArrayLength instructions
+  // we need to make sure that they depend on the same map check and that
+  // they have the same type (hopefully Smi and not Tagged).
+  // In this method we group all HJSArrayLength insts by the array they
+  // operate on and try to make the checks uniform in each group.
+  void ProcessJSArrayLengths();
+
  private:
   HConstant* GetConstant(SetOncePointer<HConstant>* pointer,
                          Handle<Object> value);
@@ -397,6 +408,7 @@ class HGraph: public ZoneObject {
   ZoneList<HBasicBlock*> blocks_;
   ZoneList<HValue*> values_;
   ZoneList<HPhi*>* phi_list_;
+  ZoneList<HJSArrayLength*> array_lengths_;
   ZoneList<HInstruction*>* uint32_instructions_;
   SetOncePointer<HConstant> undefined_constant_;
   SetOncePointer<HConstant> constant_1_;