[ValueTracking] Teach isKnownNonNullFromDominatingCondition about AND

`isKnownNonNullFromDominatingCondition` is able to prove non-null basing on `br` or `guard`
by `%p != null` condition, but is unable to do so basing on `(%p != null) && %other_cond`.
This patch allows it to do so.

Differential Revision: https://reviews.llvm.org/D50172
Reviewed By: reames


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@338990 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed