Reduce strength of ModI for power-of-2 divisor.

src/hydrogen-instructions.h

 // Copyright 2011 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 2549 matching lines @@
   virtual Range* InferRange();
 };
 
 
 class HMod: public HArithmeticBinaryOperation {
  public:
   HMod(HValue* left, HValue* right) : HArithmeticBinaryOperation(left, right) {
     SetFlag(kCanBeDivByZero);
   }
 
+  bool HasPowerOf2Divisor() {
+    if (right()->IsConstant() &&
+        HConstant::cast(right())->HasInteger32Value()) {
+      int32_t value = HConstant::cast(right())->Integer32Value();
+      return value != 0 && (IsPowerOf2(value) || IsPowerOf2(-value));
+    }
+
+    return false;
+  }
+
   virtual HValue* EnsureAndPropagateNotMinusZero(BitVector* visited);
 
   DECLARE_CONCRETE_INSTRUCTION(Mod, "mod")
 
  protected:
   virtual bool DataEquals(HValue* other) { return true; }
 
   virtual Range* InferRange();
 };
 
@@ skipping 871 matching lines @@
   HValue* object() { return left(); }
   HValue* key() { return right(); }
 };
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_