Hello Ian. I have one more question. If I have, for example, a define_insn rtx which matches a pattern generated by previous define_expand rtx. define_expand and define_split combination produces either a simple "set" rtx or "set" plus clobber of CC reg. And if in define_insn I specify a constraint that requires such an operand type which should generate a CC clobber, but initially there could be a combination of operands that does not clobber a CC and also does not satisfy constraints, so compiler must reload one or two operands in appropriate registers which satisfies constraints. In the case those appropriate registers should clobber a CC does a compiler add a suitable clobber rtx as written in define_split, or it just changes the registers names without any knowledge of a necessary clobber? Thanks Dmitry. --- Исходное сообщение --- От кого: "Ian Lance Taylor" <iant@xxxxxxxxxx> Кому: "Dmitry" <mittie@xxxxxxx> Дата: 28 апреля 2011, 17:58:17 Тема: Re: Back end question. > "Dmitry" <mittie@xxxxxxx> writes: > > > But is there a chance that between a rtl generation and splitting an insn, a compiler could use that clobbered CC reg in some of intermediate phases, but after a register allocation it turns out that there shouldn't be any clobber at all? > > Yes, there is a chance that that could happen. If you are lucky you > will be able to clean it up after the splitting and reload, by observing > the redundant set. > > Ian > >
