[witty_username]

The LLVM docs say that clang uses mem2reg for mutable local variables, so it can't be very slow.

From the end of

http://llvm.org/docs/tutorial/LangImpl7.html#memory-in-llvm

> Proven and well tested: clang uses this technique for local mutable variables. As such, the most common clients of LLVM are using this to handle a bulk of their variables. You can be sure that bugs are found fast and fixed early.