SeparateConstOffsetFromGEP can gives more optimizaiton opportunities related to GEPs, which benefits EarlyCSE
and LICM. By enabling these passes we can have better address calculations and generate a better addressing
mode. Some SPEC 2006 benchmarks (astar, gobmk, namd) have obvious improvements on Cortex-A57.
Reviewed in http://reviews.llvm.org/D5864.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222331 91177308-0d34-0410-b5e6-96231b3b80d8
