Software fault isolation (SFI) is an important technique for the construction of secure operating systems, web browsers, and other extensible software. We demonstrate that superoptimization can dramatically improve the performance of Google Native Client, a SFI system that ships inside the Google Chrome Browser. Key to our results are new techniques for superoptimization of loops: we propose a new architecture for superoptimization tools that incorporates both a fully sound verification technique to ensure correctness and a bounded verification technique to guide the search to optimized code. In our evaluation we optimize 13 libc string functions, formally verify the correctness of the optimizations and report a median and average speedup of 25% over the libraries shipped by Google.

The maturation of the Web platform has given rise to sophisticated and demanding Web applications such as interactive 3D visualization, audio and video software, and games. With that, efficiency and security of code on the Web has become more important than ever. Yet JavaScript as the only built-in language of the Web is not well-equipped to meet these requirements, especially as a compilation target.