[ImplicitNullChecks] Support unordered atomic accesses

Update the INC pass to allow folding unordered atomics.  This is the first optimization unblocked by the changes landed from D57601.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@356006 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed