Flexible representation for BuildIncrement, but CannotBeTagged.

src/hydrogen-instructions.cc

Index: src/hydrogen-instructions.cc
diff --git a/src/hydrogen-instructions.cc b/src/hydrogen-instructions.cc
index 5ec663c47b29460c823cf8579471fab7e8e37f21..b43c6715f2473bdd634e30bbde3da2574daf9c85 100644
--- a/src/hydrogen-instructions.cc
+++ b/src/hydrogen-instructions.cc
@@ -128,6 +128,7 @@ void HValue::UpdateRepresentation(Representation new_rep,
                                   const char* reason) {
   Representation r = representation();
   if (new_rep.is_more_general_than(r)) {
+    if (CheckFlag(kCannotBeTagged) && r.IsTagged()) return;
     if (FLAG_trace_representation) {
       PrintF("Changing #%d %s representation %s -> %s based on %s\n",
              id(), Mnemonic(), r.Mnemonic(), new_rep.Mnemonic(), reason);