On Fri, 23 Sep 2011 09:30:48 -0400, amylaar wrote: > Hiding the flags register would mean it is not represented in the rtl at > all. You can have combined compare-branch instructions. Of course, > going that route would mean that the model you present to GCC is even > further from the hardware than one that uses cc0. >
Got it! That seems that it would go against the whole point of replacing cc0 for CC_REGNUM in my specific case. Oh well... >> What I currently have in mind is to have a backend macro listing all >> the move for which a move clobber CC_REG, then whenever GCC generates a >> move, it queries the macro to know if the move requires clobbering and >> emits the clobber if required. However, I am unsure how deep the rabbit >> hole goes. > > Oh, so you do have variants that can do without the clobber. Actually I don't... My explanation was supposed to be referring to a general solution. In my case, the macro would list all moves since all moves clobber CC. > If you can > make all the reloads without introducing explicit flag clobbers, that it > should work. Unfortunately I can't. > But you can't just pull a flag clobber out of thin air. Understood. > You should have > some way to generate valid code when the flags register is unavailable / > must be saved. Then you can use peephole2 to add flag clobbers where > the flags register is available. > > Or you can use machine_dependent_reorg or another machine-specific pass > inserted with the pass manager to rewrite clobber-free instructions into > ones that have a hardware equivalent; but you must make sure that your > data flow remains sound in the process. I think your last suggestion of having a pass to rewrite the clobber free instructions into one with a hardware equivalent seems the one to go for me. Thanks for the suggestions, -- PMatos
