Similar in spirit to D20497 :
If all elements of a constant vector are known non-zero, then we can say that the
whole vector is known non-zero.
It seems like we could extend this to FP scalar/vector too, but isKnownNonZero()
says it only works for integers and pointers for now.
Differential Revision: http://reviews.llvm.org/D20544
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@270562 91177308-0d34-0410-b5e6-96231b3b80d8
