Internalize strings in-place

src/runtime/runtime-strings.cc

 // Copyright 2014 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/runtime/runtime-utils.h"
 
 #include "src/arguments.h"
 #include "src/regexp/jsregexp-inl.h"
 #include "src/string-builder.h"
 #include "src/string-search.h"
@@ skipping 244 matching lines @@
       Object* first = fixed_array->get(0);
       if (first->IsString()) return first;
     }
     length = StringBuilderConcatLength(special_length, fixed_array,
                                        array_length, &one_byte);
   }
 
   if (length == -1) {
     return isolate->Throw(isolate->heap()->illegal_argument_string());
   }
+  if (length == 0) {
+    return isolate->heap()->empty_string();
+  }
 
   if (one_byte) {
     Handle<SeqOneByteString> answer;
     ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
         isolate, answer, isolate->factory()->NewRawOneByteString(length));
     StringBuilderConcatHelper(*special, answer->GetChars(),
                               FixedArray::cast(array->elements()),
                               array_length);
     return *answer;
   } else {
@@ skipping 724 matching lines @@
   SealHandleScope shs(isolate);
   DCHECK(args.length() == 2);
   if (!args[0]->IsString()) return isolate->heap()->undefined_value();
   if (!args[1]->IsNumber()) return isolate->heap()->undefined_value();
   if (std::isinf(args.number_at(1))) return isolate->heap()->nan_value();
   return __RT_impl_Runtime_StringCharCodeAtRT(args, isolate);
 }
 
 }  // namespace internal
 }  // namespace v8