On Fri, Jun 28, 2013 at 6:39 PM, Eric Botcazou <ebotca...@adacore.com> wrote: >> The problem is auto-inc-dec is weak and can only capture >> post-increment in first part of code, generating even worse code for >> RA: >> .L1: >> r197 <- r162 >> [r197++] <- x >> ... >> [r162+4] <- y >> r162 <- r197+0x4 >> ... >> b .L1 >> Now we have two live registers and it seems hard to eliminate. >> >> So could the unrolled codes be like below? > > I'd try the opposite first, i.e to do more renaming so as to get smaller live > ranges for the pseudo-registers and thus help the auto-inc-dec and RA passes.
Hi Eric, Thanks for your explanation. It seems the unroller tends to replace: use(i) i = i + 1; ... use(i) i = i + 1; ... use(i) i = i + 1; ... type of codes by: use(i) i0 = i + 1 ... use(i) i = i0 + 1 ... use(i) i = i0 + 2 ... I understand this splits long live range of "i" into short ones, but since we have -fweb pass which does below transformation: use(i) i = i + 1; ... use(i) i = i + 1; ... use(i) i = i + 1; ... into: use(i) i0 = i + 1 ... use(i0) i1 = i0 + 1 ... use(i1) i = i0 + 2 ... Why would we want "-fsplit-ivs-in-unroller" in the first place? As far as live range is concerned, it seems "-fweb" works as good as "-fsplit-ivs-in-unroller". Thanks in advance. -- Best Regards.
