I'm not entirely sure whether this is worth an RFC, but, just in case.
On bugzilla Eli pointed out we currently match a specific sequence of
instructions to cls (
rGb9a0551862fb), and given how fragile this is, it
could be better to just introduce an intrinsic for it (and presumably,
teach peephole optimizations to lower a sequence to that intrinsic).
I wonder what folks are OK with the new intrinsic.
If there are no strong objections, I'll proceed with a patch.