As I understand it, one thing LLVM can do that GCC can't is run-time compilation and optimization: generating code on the fly and compiling it to run at native

As I understand it, one thing LLVM can do that GCC can't is run-time compilation and optimization: generating code on the fly and compiling it to run at native speeds, maybe also profiling several different versions and picking the best. This is only possible if you have significant chunks of a compiler built into your application. If you were to attempt the same with GCC, your application would need to be GPLed.