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From: "burnus at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug fortran/46900] New: 50% slowdown when linking with LTO in a single step Date: Sun, 12 Dec 2010 10:31:00 -0000 [thread overview] Message-ID: <bug-46900-4@http.gcc.gnu.org/bugzilla/> (raw) http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46900 Summary: 50% slowdown when linking with LTO in a single step Product: gcc Version: 4.6.0 Status: UNCONFIRMED Keywords: missed-optimization Severity: normal Priority: P3 Component: fortran AssignedTo: unassigned@gcc.gnu.org ReportedBy: burnus@gcc.gnu.org Cf. PR 44334 for another LTO slowdown. Cf. http://gcc.gnu.org/ml/fortran/2010-12/msg00067.html I had expected that doing the LTO linkage in one or in two steps is identical, but seemingly it is not: $ gfortran -fexternal-blas -flto -Ofast -march=native \ test.f90 dgemm.f lsame.f xerbla.f $ ./a.out Time, MATMUL: 1.4680910 53.480084765505403 dgemm: 1.4720919 56.452265589399069 But if one first compiles and then links (w/ or w/o LTO), the programm is 47% faster: $ gfortran -fexternal-blas -Ofast -march=native \ test.f90 dgemm.f lsame.f xerbla.f Time, MATMUL: 1.0080630 53.480084765505403 dgemm: 1.0200630 56.452265589399069 $ gfortran -c -fexternal-blas -flto -Ofast -march=native \ test.f90 dgemm.f lsame.f xerbla.f $ gfortran -flto -Ofast -march=native test.o dgemm.o lsame.o xerbla.o $ ./a.out Time, MATMUL: 1.0080630 53.480084765505403 dgemm: 1.0080630 56.452265589399069 (If one
next reply other threads:[~2010-12-12 10:31 UTC|newest] Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top 2010-12-12 10:31 burnus at gcc dot gnu.org [this message] 2010-12-12 10:33 ` [Bug middle-end/46900] " burnus at gcc dot gnu.org 2010-12-12 10:34 ` burnus at gcc dot gnu.org 2010-12-12 10:39 ` [Bug middle-end/46900] [4.6 Regression] " burnus at gcc dot gnu.org 2010-12-12 10:50 ` burnus at gcc dot gnu.org 2010-12-16 14:40 ` rguenth at gcc dot gnu.org 2010-12-16 15:24 ` burnus at gcc dot gnu.org 2010-12-17 12:14 ` d.g.gorbachev at gmail dot com 2011-01-19 17:10 ` rguenth at gcc dot gnu.org 2011-01-19 22:11 ` burnus at gcc dot gnu.org
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