[Analysis] bitreverse(undef) returns undef

Summary:
The reverse of an artbitrary bitpattern is also an arbitrary
bitpattern.

Reviewers: trentxintong, arsenm, majnemer

Reviewed By: majnemer

Subscribers: majnemer, wdng, llvm-commits

Differential Revision: https://reviews.llvm.org/D31118

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@298201 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed