[LCG] Add some pedantry to the use of ptrdiff_t to appease build bots.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207337 91177308-0d34-0410-b5e6-96231b3b80d8
DAGCombiner: Simplify code a bit, make more transforms work with vectors.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207338 91177308-0d34-0410-b5e6-96231b3b80d8