On Sun, Jan 18, 2015 at 04:26:27PM -0500, Hans-Peter Nilsson wrote: > For targets where most insns set condition-codes (and that don't > use the deprecated CC0-machinery), those insns will always be > expressed using a parallel with (most often) two members, one > being the "main" part of the insn and the other either a > (clobber (reg:CC ...)) or a (set (reg:CC ...) ...). > > There, it doesn't make sense to have a different canonical > order. For example: people have already brought up error-prone > operand renumbering as a problem, from the perspective of > changing *from* the compare-elim (aka. swapped) order.
You don't need to renumber operands, operand numbers can be in any order. A big nuisance though is having to move all your match_dups and match_operands around (the latter should be first always). Although that can be fixed in gen* as well of course. > Conversely, if it was declared canonical, you'd have to more > often perform otherwise needless operand renumbering in bodies > of define_expand's and define_insns (where you hopefully use > e.g. define_subst to avoid pattern explosion), when you need to > refer to the operands of the "main", non-cc part, for both the > set and the clobber substitution. I wish I could use define_subst, but it a) is not generic enough for most uses, and b) does not handle splitters at all :-( That is something for a different discussion though. Segher
