In a micro benchmark, using the clang version appears to be a bit faster. However, note that code size can also become a relevant concern in larger code bases:

In a micro benchmark, using the clang version appears to be a bit faster. However, note that code size can also become a relevant concern in larger code bases: Apple, for example, is said to generally build its OS code with -Os rather than -O2 or -O3 (and had -Oz as an even more aggressive custom code size optimization added to gcc back when they still were using it instead of clang).