[crankshaft] only compile string index access with element key.

src/crankshaft/hydrogen.cc

 // Copyright 2013 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.
 
 #include "src/crankshaft/hydrogen.h"
 
 #include <sstream>
 
 #include "src/allocation-site-scopes.h"
 #include "src/ast-numbering.h"
@@ skipping 7858 matching lines @@
   ValueContext for_value(this, ARGUMENTS_NOT_ALLOWED);
   Push(object);
   if (key != NULL) Push(key);
   BuildLoad(expr, expr->LoadId());
 }
 
 
 void HOptimizedGraphBuilder::BuildLoad(Property* expr,
                                        BailoutId ast_id) {
   HInstruction* instr = NULL;
-  if (expr->IsStringAccess()) {
+  if (expr->IsStringAccess() && expr->GetKeyType() == ELEMENT) {
     HValue* index = Pop();
     HValue* string = Pop();
     HInstruction* char_code = BuildStringCharCodeAt(string, index);
     AddInstruction(char_code);
     instr = NewUncasted<HStringCharFromCode>(char_code);
 
   } else if (expr->key()->IsPropertyName()) {
     Handle<String> name = expr->key()->AsLiteral()->AsPropertyName();
     HValue* object = Pop();
 
@@ skipping 5740 matching lines @@
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 }  // namespace internal
 }  // namespace v8