[ARM] Combine BFIs together

[ARM] Combine BFIs together

If we have a chain of BFIs, we may be able to combine several together into one merged BFI. We can do this if the "from" bits from one BFI OR'd with the "from" bits from the other BFI form a contiguous range, and the same with the "to" bits.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@252740 91177308-0d34-0410-b5e6-96231b3b80d8