[pmarin]

Not answering your question but in my experience reading assembly output of the two compilers the unoptimized output of Clang is atrocious while GCC is closer of what a human could have wrote. Clang seems to have to do better in optimization passes to archive similar results. Usually Clang was a faster compiler in O1 but I don’t think it’s true anymore.

[PeCaN]

that's just because gcc has certain optimization passes that can't be disabled

(that said gcc -O0 is still absolutely nothing like what a human would write)