Summary:
This is especially important for targets that use multiple address spaces,
and commonly place global variables in address spaces other than zero.
Fixes PR22383
Test Plan: New test case added: llvm-used.cu
Reviewers: jingyue
Subscribers: llvm-commits
Differential Revision: http://reviews.llvm.org/D7345
llvm-svn: 227861
Justin Holewinski