Support use of external strings as inputs to LoadCodeUnitsInstr.

runtime/vm/intermediate_language.h

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_INTERMEDIATE_LANGUAGE_H_
 #define VM_INTERMEDIATE_LANGUAGE_H_
 
 #include "vm/allocation.h"
 #include "vm/ast.h"
 #include "vm/growable_array.h"
@@ skipping 3677 matching lines @@
   LoadCodeUnitsInstr(Value* str,
                      Value* index,
                      intptr_t element_count,
                      intptr_t class_id,
                      intptr_t token_pos)
       : class_id_(class_id),
         token_pos_(token_pos),
         element_count_(element_count),
         representation_(kTagged) {
     ASSERT(element_count == 1 || element_count == 2 || element_count == 4);
-    ASSERT(class_id == kOneByteStringCid || class_id == kTwoByteStringCid);
+    ASSERT(RawObject::IsStringClassId(class_id));
     SetInputAt(0, str);
     SetInputAt(1, index);
   }
 
   intptr_t token_pos() const { return token_pos_; }
 
   DECLARE_INSTRUCTION(LoadCodeUnits)
   virtual CompileType ComputeType() const;
 
   bool IsExternal() const {
@@ skipping 497 matching lines @@
   LoadUntaggedInstr(Value* object, intptr_t offset) : offset_(offset) {
     SetInputAt(0, object);
   }
 
   virtual Representation representation() const {
     return kUntagged;
   }
   DECLARE_INSTRUCTION(LoadUntagged)
   virtual CompileType ComputeType() const;
 
+  virtual Representation RequiredInputRepresentation(intptr_t idx) const {
+    ASSERT(idx == 0);
+    // The object may be tagged or untagged (for external objects).
+    return kNoRepresentation;
+  }
+
   Value* object() const { return inputs_[0]; }
   intptr_t offset() const { return offset_; }
 
   virtual bool CanDeoptimize() const { return false; }
 
   virtual EffectSet Effects() const { return EffectSet::None(); }
   virtual bool AttributesEqual(Instruction* other) const { return true; }
 
  private:
   intptr_t offset_;
@@ skipping 3744 matching lines @@
       Isolate* isolate, bool opt) const {                                     \
     UNIMPLEMENTED();                                                          \
     return NULL;                                                              \
   }                                                                           \
   void Name::EmitNativeCode(FlowGraphCompiler* compiler) { UNIMPLEMENTED(); }
 
 
 }  // namespace dart
 
 #endif  // VM_INTERMEDIATE_LANGUAGE_H_