Merge isKnownNonNull into isKnownNonZero
It now knows the tricks of both functions.
Also, fix a bug that considered allocas of non-zero address space to be always non null

Differential Revision: https://reviews.llvm.org/D37628

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@312869 91177308-0d34-0410-b5e6-96231b3b80d8
17 files changed