When I started at Google, I sat next to a guy who used to write compilers for DEC and Intel. I asked him, given the huge amount Google spends on hardware and electricity, if he thought that switching to ICC was worth while. His answer was basically that ICC is tuned to maximally exploit undefined behavior for marketing purposes and he wouldn't want to use it in production, at least without heavily tweaking flags to disable some optimizations. ICC gets most of its speed advantages by enabling optimizations that are present in GCC/Clang, but deemed too dangerous to turn on by default.

clang with "-Ofast"; I really wonder, which other options are there?! And imho this just doesn't explain the 200% difference?

And some other things which are bugging me:

- can you only optimize for A53 on Android with the big.LITTLE-configurations (they do!)?

- so they cross-compiled an AMD64-producing gcc 3.2 with Xcode 10 on MacOS-X for ARM? impressive.