[NVPTX] Auto-upgrade some NVPTX intrinsics to LLVM target-generic code.
Summary:
Specifically, we upgrade llvm.nvvm.:
* brev{32,64}
* clz.{i,ll}
* popc.{i,ll}
* abs.{i,ll}
* {min,max}.{i,ll,u,ull}
* h2f
These either map directly to an existing LLVM target-generic
intrinsic or map to a simple LLVM target-generic idiom.
In all cases, we check that the code we generate is lowered to PTX as we
expect.
These builtins don't need to be backfilled in clang: They're not
accessible to user code from nvcc.
Reviewers: tra
Subscribers: majnemer, cfe-commits, llvm-commits, jholewinski
Differential Revision: https://reviews.llvm.org/D28793
llvm-svn: 292694