Use of register 17 on x86

[Richard Kenner]

There is a choice of using a SCRATCH with that register class or the
explicit register 17.  If the former, gcse can move such computation, but
we may try to move things using that class out of loops and have to do
expensive moves in and out of CC.

Has any thought been given to this tradeoff?

Also, why isn't x86 using CC0 anymore?  That would seem to be the most
efficient, both in terms of generated code and compilation speed.