SynthesisOS (http://valerieaurora.org/synthesis/SynthesisOS/ http://valerieaurora.org/synthesis/SynthesisOS/) used an optimizing assembler to recompile the oper

SynthesisOS (http://valerieaurora.org/synthesis/SynthesisOS/ http://valerieaurora.org/synthesis/SynthesisOS/) used an optimizing assembler to recompile the operating system on the fly (think of it as the OS being JITed). The reason it had to use an optimizing assembler is because the operating system itself was written in assembler (MC68030). It could run SunOS binaries faster than SunOS on the same hardware. And this was done back in 1992, when the major debate was Assembler vs. C (back when C was considered "high level").