https://gcc.gnu.org/bugzilla/show_bug.cgi?id=18154
--- Comment #10 from David Edelsohn <dje at gcc dot gnu.org> --- isel is not generally performance win for Power using GCC. It is enabled for LLVM because LLVM has a simplistic basic block scheduler and isel allows LLVM to form larger basic blocks to provide the scheduler with more freedom of movement.
