Рассказы про прогрессивность и высокое качество LLVM вообще сильно преувеличены.

"I think that it is more like some base LLVM main architecture flaw that prevent to catch GCC in code quality. I remember 4+ years ago articles that state LLVM was so good, and we have LLVM based radeon shader that lag behind Catalyst, OpenMP still not implemented, code quality lag behind GCC with exception of few anecdotal special selected cases, etc."
--http://www.phoronix.com/forums/showthread.php?94338-LLVM-Cla...

"o LLVM 3.2 -> 3.3: No progress, even small 64-bit peak degradation (0.6%)
o GCC4.7-> 4.8: Steady progress (1%-4%)"
--http://article.gmane.org/gmane.comp.gcc.devel/134152