inariant.group handling in GVN

inariant.group handling in GVN

The most important part required to make clang
devirtualization works ( ͡°͜ʖ ͡°).
The code is able to find non local dependencies, but unfortunatelly
because the caller can only handle local dependencies, I had to add
some restrictions to look for dependencies only in the same BB.

http://reviews.llvm.org/D12992

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@249196 91177308-0d34-0410-b5e6-96231b3b80d8