Flexible representation for BuildIncrement, but CannotBeTagged.

src/hydrogen-instructions.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 765 matching lines @@
 
 typedef EnumSet<GVNFlag> GVNFlagSet;
 
 
 class HValue: public ZoneObject {
  public:
   static const int kNoNumber = -1;
 
   enum Flag {
     kFlexibleRepresentation,
+    kCannotBeTagged,
     // Participate in Global Value Numbering, i.e. elimination of
     // unnecessary recomputations. If an instruction sets this flag, it must
     // implement DataEquals(), which will be used to determine if other
     // occurrences of the instruction are indeed the same.
     kUseGVN,
     // Track instructions that are dominating side effects. If an instruction
     // sets this flag, it must implement SetSideEffectDominator() and should
     // indicate which side effects to track by setting GVN flags.
     kTrackSideEffectDominators,
     kCanOverflow,
@@ skipping 87 matching lines @@
   void set_id(int id) { id_ = id; }
 
   HUseIterator uses() const { return HUseIterator(use_list_); }
 
   virtual bool EmitAtUses() { return false; }
   Representation representation() const { return representation_; }
   void ChangeRepresentation(Representation r) {
     ASSERT(CheckFlag(kFlexibleRepresentation));
     RepresentationChanged(r);
     representation_ = r;
-    if (r.IsTagged()) {
+    if (r.IsTagged() ||
+        (r.IsDouble() && CheckFlag(kCannotBeTagged))) {
       // Tagged is the bottom of the lattice, don't go any further.
       ClearFlag(kFlexibleRepresentation);
     }
   }
   virtual void AssumeRepresentation(Representation r);
 
   virtual Representation KnownOptimalRepresentation() {
     Representation r = representation();
     if (r.IsTagged()) {
       HType t = type();
@@ skipping 5704 matching lines @@
   virtual bool IsDeletable() const { return true; }
 };
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_