isDereferenceablePointer: look through gc.relocate calls

While a theoretical GC might change dereferenceability on collection,
there is no such known collector and no need to account for the case
with a flag yet.

Differential Revision: http://reviews.llvm.org/D7454

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@228606 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed