Reapply r186316 with a fix for one bug where the code could walk off the
end of a vector. This was found with ASan. I've had one other report of
a crasher, but thus far been unable to reproduce the crash. It may well
be fixed with this version, and if not I'd like to get more information
from the build bots about what is happening.

See r186316 for the full commit log for the new implementation of the
SROA algorithm.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186565 91177308-0d34-0410-b5e6-96231b3b80d8
Fix copy and paste bug from r186491 to make v2f64 use MOVAPD/MOVUPD as it should.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186566 91177308-0d34-0410-b5e6-96231b3b80d8