[SystemZ] Add a mapping from "select register" to "load on condition" (2-addr).
The SELR(Mux) instructions can be converted to two-address form as LOCR(Mux)
instructions whenever one of the sources are the same reg as dest. By adding
this mapping in getTwoOperandOpcode(), we get:
- Two-address hints in getRegAllocationHints() for select register instructions.
- No need anymore for special handling in SystemZShortenInst.cpp - shortenSelect() removed.
The two-address hints are now added before the GRX32 hints, which should be
Review: Ulrich Weigand