Make HJSArrayLength more likely to have identical GVNs.

src/hydrogen.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 352 matching lines @@
     return is_recursive_;
   }
 
   void RecordUint32Instruction(HInstruction* instr) {
     if (uint32_instructions_ == NULL) {
       uint32_instructions_ = new(zone()) ZoneList<HInstruction*>(4, zone());
     }
     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);
   HConstant* GetConstantInt32(SetOncePointer<HConstant>* pointer,
                               int32_t integer_value);
 
   void MarkAsDeoptimizingRecursively(HBasicBlock* block);
   void InsertTypeConversions(HInstruction* instr);
   void PropagateMinusZeroChecks(HValue* value, BitVector* visited);
   void RecursivelyMarkPhiDeoptimizeOnUndefined(HPhi* phi);
   void InsertRepresentationChangeForUse(HValue* value,
                                         HValue* use_value,
                                         int use_index,
                                         Representation to);
   void InsertRepresentationChangesForValue(HValue* value);
   void InferTypes(ZoneList<HValue*>* worklist);
   void InitializeInferredTypes(int from_inclusive, int to_inclusive);
   void CheckForBackEdge(HBasicBlock* block, HBasicBlock* successor);
   void EliminateRedundantBoundsChecks(HBasicBlock* bb, BoundsCheckTable* table);
 
   Isolate* isolate_;
   int next_block_id_;
   HBasicBlock* entry_block_;
   HEnvironment* start_environment_;
   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_;
   SetOncePointer<HConstant> constant_minus1_;
   SetOncePointer<HConstant> constant_true_;
   SetOncePointer<HConstant> constant_false_;
   SetOncePointer<HConstant> constant_hole_;
   SetOncePointer<HArgumentsObject> arguments_object_;
 
   SetOncePointer<HBasicBlock> osr_loop_entry_;
@@ skipping 1117 matching lines @@
   const char* filename_;
   HeapStringAllocator string_allocator_;
   StringStream trace_;
   int indent_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_H_