507d823392
This avoids a downstream regression where LSR prefers {-1,+1}.
When constant zero typically doesn't require preheader initialization
(queried via TTI::getIntImmCost), consider it as free in getSetupCost.
Three test changes are improvements: amx-across-func.ll,
2011-11-29-postincphi.ll and pr62660-normalization-failure.ll.
Other test changes are neutral.