BBVectorize: Better use of TTI->getShuffleCost

When flipping the pair of subvectors that form a vector, if the
vector length is 2, we can use the SK_Reverse shuffle kind to get
more-accurate cost information. Also we can use the SK_ExtractSubvector
shuffle kind to get accurate subvector extraction costs.

The current cost model implementations don't yet seem complex enough
for this to make a difference (thus, there are no test cases with this
commit), but it should help in future.

Depending on how the various targets optimize and combine shuffles in
practice, we might be able to get more-accurate costs by combining the
costs of multiple shuffle kinds. For example, the cost of flipping the
subvector pairs could be modeled as two extractions and two subvector
insertions. These changes, however, should probably be motivated
by specific test cases.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173621 91177308-0d34-0410-b5e6-96231b3b80d8
[XCore] Add missing 0r instructions.

These instructions are not targeted by the compiler but they are
needed for the MC layer.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173623 91177308-0d34-0410-b5e6-96231b3b80d8
[XCore] Add missing 1r instructions.

These instructions are not targeted by the compiler but they are
needed for the MC layer.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173624 91177308-0d34-0410-b5e6-96231b3b80d8