This recent presentation from the 2013 European LLVM Conference outlines the optimization issues LLVM still suffers from, making the produced binaries up to ~10

This recent presentation from the 2013 European LLVM Conference outlines the optimization issues LLVM still suffers from, making the produced binaries up to ~10% slower than with GCC for some use cases: http://llvm.org/devmtg/2013-04/#talk3 http://llvm.org/devmtg/2013-04/#talk3