Ok but if people do not set each status bit individually, how do they set several not related bits in one CC mode and in one set rtx? --- Исходное сообщение --- От кого: "Ian Lance Taylor" <iant@xxxxxxxxxx> Кому: "Dmitry" <mittie@xxxxxxx> Дата: 4 мая 2011, 22:40:20 Тема: Re: Back end question. > "Dmitry" <mittie@xxxxxxx> writes: > > > Maybe it is better to use the separate CC modes for individual status bits, to reflect all status changes? For example > > I could define a CCZ mode for "zero" status bit, CCM mode for a "minus" status bit, and CCV mode for an "overflow" status bit. And then use a parallel of CC setters, like: > > (parallel [ > > (set (reg:CCZ ST0_REGNO) (eq:HI (match_operand:HI 0 "register_operand" "") (const_int 0))) > > (set (reg:CCM ST0_REGNO) (lt:HI (match_dup 0) (const_int 0))) > > (set (reg:CCV ST0_REGNO) (gt:HI (match_dup 0) (const_int 65535))) > > ] > > ) > > And then the compiler could test CC reg for branch or conditional insns in any of defined above modes to check whether a corresponding bit is set or not? > > You could do that, yes, but not like this. Instead, you would give a > different register number to each status bit, and you would use them all > in CCmode. The main reason people don't use this approach is that many > instructions set several of the status bits. > > Ian > >
