Basically the pattern to optimize is:
inject_enum_addr %stackloc, #SomeCase
switch_enum_addr %stackloc ...
This works even if the enum is resilient and the case does not have a payload. As long as we don't have opaque values in SIL we need this peephole to optimize the pattern.
This change fixes the code generation for Float.rounded().
rdar://problem/46353885
