On Jun 5, 2012, at 6:46 AM, Paolo Bonzini wrote: >> Do we always have CTZ if we have FFS? Can't there be a target that >> implements FFS as opcode but not CTZ, so you'd slow down things? >> Thus, should the transform be conditonal on target support for CTZ >> or no target support for FFS? > > Hmm, SH and (some semi-obscure variant of) SPARC. But actually SPARC > should define a clz pattern instead; SH should have a popcount pattern + > a generic trick to expand ctz/ffs in terms of popcount. I'll submit > those before applying this patch.
VAX has both FFS/FFC instructions but only a ffs pattern. It does not have CTZ or CTO patterns but those could be added trivially.
