The main use for this patch is LTO. It is not (yet?) possible to set the
size level (-Os, -Oz) in the linker, which means loops are still rotated
even if -Oz is specified on the command line. Therefore, look at the
function attribute instead of only at the size level to determine
whether to rotate loops for a given function.
For discussion, see: https://reviews.llvm.org/D119342
An older version of this patch was already approved at
https://reviews.llvm.org/D119342 but I never got around to committing
it. The code changed so I had to make some minor updates to this patch
and in the meantime I also lost commit access because I wasn't really
using it. So here is an updated patch.
91722a4a13