Reapply [FastISel][AArch64] Make use of the zero register when possible (r215591).
Note: This was originally reverted to track down a buildbot error. Reapply
without any modifications.
Original commit message:
This change materializes now the value "0" from the zero register.
The zero register can be folded by several instruction, so no
materialization is need at all.
Fixes <rdar://problem/
17924413>.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216009
91177308-0d34-0410-b5e6-
96231b3b80d8