> -----Original Message----- > From: Richard Earnshaw > Sent: Thursday, April 18, 2013 5:25 PM > To: Steven Bosscher > Cc: Bin Cheng; gcc-patches@gcc.gnu.org > Subject: Re: [PATCH ARM]Extend thumb1_reorg to save more comparison > instructions > > On 18/04/13 09:20, Steven Bosscher wrote: > > On Thu, Apr 18, 2013 at 7:34 AM, Bin Cheng wrote: > >> Hi, > >> Before thumb1_reorg, ARM backend uses peephole to save comparison > >> instructions when a flag setting move is found before branch instruction. > >> Since we are using thumb1_reog now, it can be extended to catch more > >> opportunities by searching flag setting move instruction before > >> branch, rather than only the exact one before branch. > >> For example: > >> > >> mov r0, r1 > >> //other insns does not kill r0 > >> branch if (r0 == 0) > >> //other insns > >> > >> Tested on thumb1, is it OK? > > > > Isn't this something you could use compare-elim.c for instead of a > > target specific pass? > > > > Ciao! > > Steven > > > > I haven't looked at compare-elim, but probably not. Thumb1 doesn't use > cc1 and doesn't expose flag setting instructions in a MI manner (since add > instructions clobber the flags). As such it needs private back-end data to > work out what's safe.
Yes, so far the pass is disabled on ARM. I have another question, would it be better for this pass be postponed to late rtl phase, since it and scheduler (other passes) may meddle with each other? Thanks.
