Hopefully this is the non-problematic part from https://reviews.llvm.org/rL342148, which later got reverted in r342336 (b09a8c9bd9b819741b38071a7ccd95042ef2643a) due to problems with the llvm-exegesis part of the change. That part would also still be desirable, but currently appears not to be possible (https://reviews.llvm.org/D81922).
I think this should replace https://reviews.llvm.org/D44650, per Keno's comment there.