> -----Original Message----- > From: Jeff Law [mailto:l...@redhat.com] > Sent: Friday, September 05, 2014 12:45 PM > To: Zhenqiang Chen > Cc: gcc-patches@gcc.gnu.org > Subject: Re: [PATCH, ira] Miss checks in split_live_ranges_for_shrink_wrap > > On 09/01/14 02:13, Zhenqiang Chen wrote: > > > > To split live-range of register, split_live_ranges_for_shrink_wrap > > will introduce additional register copies. If such copies can not be > > optimized by later optimizations, it will lead to code size and performance > regression. > > My tests on ARM THUMB1 code size show lots of regressions due to > > additional register copies. Shrink-wrap is not enabled for ARM THUMB1, > > so I think split_live_ranges_for_shrink_wrap should not be called. > So has anyone looked at why IRA ends up selecting different registers > for the source/dest of these copies? Odds are it's just an artifact of > the heuristics in use, but I'd like to make sure there isn't something > inherently wrong happening in IRA that's causing it to not tie the source/dest > of those copies. > > > > > ChangeLog: > > 2014-09-01 Zhenqiang Chen <zhenqiang.c...@arm.com> > > > > * shrink-wrap.h: #define SHRINK_WRAPPING_ENABLED. > > * ira.c: #include "shrink-wrap.h" > > (split_live_ranges_for_shrink_wrap): Use > SHRINK_WRAPPING_ENABLED. > > * ifcvt.c: #include "shrink-wrap.h" > > (dead_or_predicable): Use SHRINK_WRAPPING_ENABLED. > > > > testsuite/ChangeLog: > > 2014-09-01 Zhenqiang Chen <zhenqiang.c...@arm.com> > > > > * gcc.target/arm/split-live-ranges-for-shrink-wrap.c: New test. > Thanks. OK for the trunk.
Thanks. The patch is installed @r215041. > As noted above, it'd may be worth spending a little time looking at the > regressions without this patch installed to see why IRA isn't doing a good job > of tying the source/dest of these copies together -- perhaps there's > something that's been overlooked and fixing it may be beneficial. I had investigated it. Compared with 4.8, the allocation order and conflict cost might be the root cause. A bug is submitted: PR63210. Thanks! -Zhenqiang > jeff >
