[NVPTX] Adds a new address space inference pass.
The old address space inference pass (NVPTXFavorNonGenericAddrSpaces) is unable
to convert the address space of a pointer induction variable. This patch adds a
new pass called NVPTXInferAddressSpaces that overcomes that limitation using a
fixed-point data-flow analysis (see the file header comments for details).
The new pass is experimental and not enabled by default. Users can turn
it on by setting the -nvptx-use-infer-addrspace flag of llc.
Reviewers: jholewinski, tra, jlebar
Subscribers: jholewinski, llvm-commits
Differential Revision: http://reviews.llvm.org/D17965