http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53346
Bug #: 53346 Summary: [4.6/4.7/4.8 Regression] Bad vectorization in the proc cptrf2 of rnflow.f90 Classification: Unclassified Product: gcc Version: 4.8.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization AssignedTo: unassig...@gcc.gnu.org ReportedBy: domi...@lps.ens.fr CC: rgue...@gcc.gnu.org, ubiz...@gmail.com At revision 187457 (i.e., with pr53340 fixed) on x86_64-apple-darwin10, after [macbook] test/dbg_rnflow% gfc -c -O3 -ffast-math -funroll-loops timctr.f90 cmpcpt.f90 cptrf2.f90 dger.f90 dgetri.f90 dswap.f90 dtrsm.f90 evlrnf.f90 idamax.f90 main.f90 mattrs.f90 cmpmat.f90 dgemm.f90 dgetf2.f90 dlaswp.f90 dtrmm.f90 dtrti2.f90 extpic.f90 ilaenv.f90 matcnt.f90 reaseq.f90 xerbla.f90 cptrf1.f90 dgemv.f90 dgetrf.f90 dscal.f90 dtrmv.f90 dtrtri.f90 gentrs.f90 lsame.f90 matsim.f90 [macbook] test/dbg_rnflow% makeo ; time a.out > /dev/null 23.872u 0.349s 0:24.22 99.9% 0+0k 0+0io 0pf+0w[macbook] test/dbg_rnflow% /opt/gcc/gcc4.8p-187339/bin/gfortran -c -O3 -ffast-math -funroll-loops evlrnf.f90 [macbook] test/dbg_rnflow% makeo ; time a.out > /dev/null 22.259u 0.346s 0:22.61 99.9% 0+0k 0+0io 0pf+0w [macbook] test/dbg_rnflow% /opt/gcc/gcc4.8p-187291/bin/gfortran -c -O3 -ffast-math -funroll-loops idamax.f90 [macbook] test/dbg_rnflow% makeo ; time a.out > /dev/null 22.252u 0.345s 0:22.60 99.9% 0+0k 0+0io 0pf+0w [macbook] test/dbg_rnflow% /opt/gcc/gcc4.8p-187102/bin/gfortran -c -O3 -ffast-math -funroll-loops idamax.f90 [macbook] test/dbg_rnflow% makeo ; time a.out > /dev/null 22.121u 0.346s 0:22.47 99.9% 0+0k 0+0io 0pf+0w (i.e., working around prpr53342 and a regression for idamax.f90, see below), the compilation of cptrf2.f90 (source attached to pr53340) with the following flags yiels optimization level 4.4.6 4.5.3 4.6.3 4.7.0 r187457 -O2 27.8 28.2 28.2 21.8 21.8 -O2 -ftree-vectorize 27.8 28.2 28.2 27.9 27.9 -O3 22.0 21.3 25.1 25.3 25.3 -O3 -fno-tree-vectorize 22.1 21.3 21.4 21.4 21.4 Note that 4.5/4.6/4.7 vectorize two loops (lines 21 and 29), while 4.8 vectorizes only the loop at line 21 (29: not vectorized: iteration count too small.). Looking at my archives I have found that a first regression appeared between revisions 162456 and 164728 optimization level 4.6-162456 4.6p-164728 -O2 28.2 28.3 -O2 -ftree-vectorize 28.1 28.3 -O3 21.4 29.4 -O3 -fno-tree-vectorize 21.3 21.4 -O3 -ffast-math 21.4 22.3 -O3 -ffast-math -funroll-loops 21.9 22.4 For the record, as said above the compilation of idamax regressed between revisions 187102 and 187291 [macbook] test/dbg_rnflow% /opt/gcc/gcc4.8p-187291/bin/gfortran -c -O3 -ffast-math -funroll-loops idamax.f90 [macbook] test/dbg_rnflow% makeo ; time a.out > /dev/null 22.252u 0.345s 0:22.60 99.9% 0+0k 0+0io 0pf+0w [macbook] test/dbg_rnflow% /opt/gcc/gcc4.8p-187102/bin/gfortran -c -O3 -ffast-math -funroll-loops idamax.f90 [macbook] test/dbg_rnflow% makeo ; time a.out > /dev/null 22.121u 0.346s 0:22.47 99.9% 0+0k 0+0io 0pf+0w Although the regression is slightly above the noise margin at the level of rnflow.f90, it could be worth to investigate it because: (1) it is a LAPACK routine (may be slightly modified), (2) there equivalent intrinsics in F90, (3) the slowdown may be quite significant at the level of the proc itself.