Box values of LoadCodeUnits that fall outside of smi range on 32bit platforms.

runtime/vm/intermediate_language_x64.cc

Index: runtime/vm/intermediate_language_x64.cc
diff --git a/runtime/vm/intermediate_language_x64.cc b/runtime/vm/intermediate_language_x64.cc
index 8aacfccf6c6fe2cba4f4094da2f8ac4ee6fb5958..261c38a224e25b43b2fff9d3bbf583c061f9d506 100644
--- a/runtime/vm/intermediate_language_x64.cc
+++ b/runtime/vm/intermediate_language_x64.cc
@@ -1131,20 +1131,6 @@ void LoadIndexedInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
 }
 
 
-Representation LoadCodeUnitsInstr::representation() const {
-  switch (class_id()) {
-    case kOneByteStringCid:
-    case kTwoByteStringCid:
-    case kExternalOneByteStringCid:
-    case kExternalTwoByteStringCid:
-      return kTagged;
-    default:
-      UNIMPLEMENTED();
-      return kTagged;
-  }
-}
-
-
 LocationSummary* LoadCodeUnitsInstr::MakeLocationSummary(Isolate* isolate,
                                                          bool opt) const {
   const intptr_t kNumInputs = 2;