strides for now, because it doesn't handle them correctly. This fixes a
miscompile of SingleSource/Benchmarks/Misc-C++/ray.
This problem was usually hidden because indvars transforms such induction
variables into negations of canonical induction variables.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@85118 91177308-0d34-0410-b5e6-96231b3b80d8
