On 06/23/2014 09:22 AM, Jeff Law wrote: > On 06/23/14 08:32, Richard Biener wrote: >> Btw, there is now no DCE after peephole2? Is peephole2 expected to >> cleanup after itself? > There were cases where we wanted to change the insns we would output to fit > into the 4:1:1 issue model of the PPro, but to do so we needed to know what > registers were live/dead so that we could rewrite the insns appropriately. It > didn't fit well into what we could do in the splitters and the old peephole > ran > too late. Dead code wasn't ever really considered. At least that's my > recollection. RTH might recall more.
Yes, peep2 was about doing what the old "peep1" rtl->text transformation did, but as an rtl->rtl transformation so we can expose the result to the scheduler. It's expected that all dead code be gone before sched2, so that the scheduler sees exactly what needs to be scheduled, and can bundle insns appropriately. I believe the peep2 pass to also want dead code to be gone, so that it gets an accurate picture of what registers are live or dead at any point. As far as I know, there are no current transformations that create new garbage. r~
