replacing the overly conservative checks that I had introduced recently to
deal with correctness issues. This makes a pretty noticable difference
in our testcases where reg_sequences are used. I've updated one test to
check that we no longer emit the unnecessary subreg moves.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@105991 91177308-0d34-0410-b5e6-96231b3b80d8
