Don't use AddSubstring for external natives

src/natives-external.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/natives.h"
 
 #include "src/base/logging.h"
 #include "src/list.h"
 #include "src/list-inl.h"
 #include "src/snapshot-source-sink.h"
@@ skipping 64 matching lines @@
       store->ReadNameAndContentPair(source);
 
     store->debugger_count_ = debugger_count;
     return store;
   }
 
  private:
   NativesStore() : debugger_count_(0) {}
 
   Vector<const char> NameFromId(const byte* id, int id_length) {
-    Vector<char> name(Vector<char>::New(id_length + 11));
-    SimpleStringBuilder builder(name.start(), name.length());
-    builder.AddString("native ");
-    builder.AddSubstring(reinterpret_cast<const char*>(id), id_length);
-    builder.AddString(".js");
-    builder.Finalize();
-    // SimpleStringBuilder wants zero-byte; the caller does not.
-    DCHECK(name[name.length() - 1] == '\0');
-    name.Truncate(name.length() - 1);
+    const char native[] = "native ";

[Sven Panne, 2014/12/18 10:32:32]

Probably not a big deal here, but note that GCC actually copies characters here.
Clang is smarter here. :-/

+    const char extension[] = ".js";
+    Vector<char> name(Vector<char>::New(id_length + sizeof(native) - 1 +
+                                        sizeof(extension) - 1));
+    memcpy(name.start(), native, sizeof(native) - 1);
+    memcpy(name.start() + sizeof(native) - 1, id, id_length);
+    memcpy(name.start() + sizeof(native) - 1 + id_length, extension,
+           sizeof(extension) - 1);
     return Vector<const char>::cast(name);
   }
 
   bool ReadNameAndContentPair(SnapshotByteSource* bytes) {
     const byte* id;
     int id_length;
     const byte* source;
     int source_length;
     bool success = bytes->GetBlob(&id, &id_length) &&
                    bytes->GetBlob(&source, &source_length);
@@ skipping 91 matching lines @@
 }
 
 
 // The compiler can't 'see' all uses of the static methods and hence
 // my choice to elide them. This we'll explicitly instantiate these.
 template class NativesCollection<CORE>;
 template class NativesCollection<EXPERIMENTAL>;
 
 }  // namespace v8::internal
 }  // namespace v8