I am trying to move towards much more space-efficient switch statements, using popcnt, as described in PR39013. This is the patch 6 towards that goal, and a continuation of D60673.
There are quite a few cases where the lookup table was smaller and it was still not used. Also, there was no consideration of how large the cases were in the calculation. These numbers will change in a later patch, (when sparse maps make switch much more compact) so we shouldn't argue too much about this cut-off.
When only an i8 is being switched over, a complete table is not large, and avoiding the branch of a regular lookup table is a significant speed win (as can be seen in the tests).