Try compiling the attached program with the following options (they differ only
in -march specification)
1. gcc -std=c99 -march=i486 -funroll-loops -fprefetch-loop-arrays
-ftree-vectorize -O3 -o gen_weyl_group gen_weyl_group.c
2. gcc -std=c99 -march=i686 -funroll-loops -fprefetch-loop-arrays
-ftree-vectorize -O3 -o gen_weyl_group gen_weyl_group.c
3. gcc -std=c99 -march=pentium-m -funroll-loops -fprefetch-loop-arrays
-ftree-vectorize -O3 -o gen_weyl_group gen_weyl_group.c
With my notebook (CPU core is Dothan) I get the following execution times:
i486 37.510
i686 37.534
p-m 53.959
Results for i486 and i686 are roughly the same, but compiling for pentium-m
results in a seriously degraded performance.
I first noted this behaviour with gcc 4.3.3 that is my system's stock compiler;
the abovementioned times were measured for 4.5.0-svn149207, so, probably, all
versions from 4.3 to 4.5 are affected by this bug.
GCC 4.5.0, used to compile the tests, was configured with the following
options:
--prefix=/home/artem/testing/gcc45 --enable-shared --enable-bootstrap
--enable-languages=c --enable-threads=posix --enable-checking=release
--with-system-zlib --with-gnu-ld --verbose --with-arch=i686
--
Summary: Optimizing for pentium-m gives worse code than
optimizing for i486
Product: gcc
Version: 4.5.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: aanisimov at inbox dot ru
GCC build triplet: i486-slackware-linux
GCC host triplet: i486-slackware-linux
GCC target triplet: i486-slackware-linux
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40644
