http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45810
Summary: 40% slowdown when using LTO for a single-file program
Product: gcc
Version: 4.6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: lto
AssignedTo: [email protected]
ReportedBy: [email protected]
That's on a Intel Core(TM)2 Duo CPU E8400 @ 3.00GHz and using CentOS Linux 5.5
(x86-64) with glibc-2.5-49.el5_5.2, binutils-2.17.50.0.6-14.el5 and
gcc version 4.6.0 20100921 (experimental) [trunk revision 164472] (GCC)
The performance for fatigue of the Polyhedron test case drops by 40% if one
enables LTO (using -fwhole=program):
gfortran -march=native -ffast-math -funroll-loops -fwhole-program
-fno-protect-parens -O3
real 0m5.115s / user 0m5.071s / sys 0m0.015s
gfortran -march=native -ffast-math -funroll-loops -flto -fwhole-program
-fno-protect-parens -O3
real 0m7.225s / user 0m7.129s / sys 0m0.017s
For the other test cases, the results are mostly similar w/ and w/o LTO though
in tendency, the non-LTO version seems to be slightly slower (but also other
programs are running now thus the results are not 100% comparable with my
previous ones at
https://users.physik.fu-berlin.de/~tburnus/gcc-trunk/benchmark/iff/ )
