Merging r167718 into 3.2 release branch

Fix PR14314

- Fix operand order for atomic sub, where the minuend is the value
  loaded from memory and the subtrahend is the parameter specified.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_32@168336 91177308-0d34-0410-b5e6-96231b3b80d8