For large YAML input, opt-viewer can take a long time. We need to provide feedback to the user about the progress.
https://reviews.llvm.org/D34735 by Brian Gesiak.
I landed https://reviews.llvm.org/D34735, which I think resolves this. There's still some room for improvement, though, in case anyone would like to write a fancier progress bar! :)
Thanks for your work!