R600: Implement computeMaskedBitsForTargetNode for BFE

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209459 91177308-0d34-0410-b5e6-96231b3b80d8
R600: Implement ComputeNumSignBitsForTargetNode for BFE

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209460 91177308-0d34-0410-b5e6-96231b3b80d8
R600: Add dag combine for BFE

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209461 91177308-0d34-0410-b5e6-96231b3b80d8
R600: Try to convert BFE back to standard bit ops when possible.

This allows existing DAG combines to work on them, and then
we can re-match to BFE if necessary during instruction selection.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209462 91177308-0d34-0410-b5e6-96231b3b80d8