Exploit dereferenceable_or_null attribute in LICM pass
Allow hoisting of loads from values marked with dereferenceable_or_null
attribute. For values marked with the attribute perform
context-sensitive analysis to determine whether it's known-non-null or
Patch by Artur Pilipenko!
Reviewers: hfinkel, sanjoy, reames
Reviewed By: reames
Differential Revision: http://reviews.llvm.org/D9253