In his work for https://reviews.llvm.org/D131960, @dongjunduo found that
the names for loops generated by getIRName could grow to be extremely
large because they are based on a serialization of the loop. Replace this with
the name of the loop (which is based on the header) and patch up the
affected lit tests.
It was suggested (in separate conversations) that an analogous
fix be made in https://reviews.llvm.org/D131960 with a FIXME
comment to resolve the 2 pieces of code so https://reviews.llvm.org/D131960
can be delivered as it is part of a GSoC project that is finishing.