Add support for adding an external and a tagged pointer

src/hydrogen-instructions.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_HYDROGEN_INSTRUCTIONS_H_
 #define V8_HYDROGEN_INSTRUCTIONS_H_
 
 #include <cstring>
 #include <iosfwd>
 
@@ skipping 4868 matching lines @@
 
  protected:
   bool DataEquals(HValue* other) override { return true; }
 
   Range* InferRange(Zone* zone) override;
 
  private:
   HAdd(HValue* context, HValue* left, HValue* right, Strength strength)
       : HArithmeticBinaryOperation(context, left, right, strength) {
     SetFlag(kCanOverflow);
+    if (left->representation().IsExternal() &&
+        right->representation().IsTagged()) {

[Jarin, 2015/07/20 08:52:32]

This looks quite brittle, perhaps we should introduce some other flag that
differentiates the special HAdd from ordinary ones.

You could then use the flag to do the right thing in
HAdd::RequiredInputRepresentation.

[Michael Starzinger, 2015/07/20 08:56:38]

+1

+      SetDependsOnFlag(kNewSpacePromotion);
+    }
   }
 };
 
 
 class HSub final : public HArithmeticBinaryOperation {
  public:
   static HInstruction* New(Isolate* isolate, Zone* zone, HValue* context,
                            HValue* left, HValue* right,
                            Strength strength = Strength::WEAK);
 
@@ skipping 3069 matching lines @@
 };
 
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_