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* [Bug c/19133] New: march=athlon can produce slower code than march=i686
@ 2004-12-22 21:01 ornati at fastwebnet dot it
2004-12-22 21:05 ` [Bug target/19133] " pinskia at gcc dot gnu dot org
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: ornati at fastwebnet dot it @ 2004-12-22 21:01 UTC (permalink / raw)
To: gcc-bugs
"gcc -v"
Reading specs from /usr/lib/gcc-lib/i686-pc-linux-gnu/3.3.4/specs
Configured with: /var/tmp/portage/gcc-3.3.4-r1/work/gcc-3.3.4/configure
--prefix=/usr --bindir=/usr/i686-pc-linux-gnu/gcc-bin/3.3
--includedir=/usr/lib/gcc-lib/i686-pc-linux-gnu/3.3.4/include
--datadir=/usr/share/gcc-data/i686-pc-linux-gnu/3.3
--mandir=/usr/share/gcc-data/i686-pc-linux-gnu/3.3/man
--infodir=/usr/share/gcc-data/i686-pc-linux-gnu/3.3/info --enable-shared
--host=i686-pc-linux-gnu --target=i686-pc-linux-gnu --with-system-zlib
--enable-languages=c,c++ --enable-threads=posix --enable-long-long
--disable-checking --disable-libunwind-exceptions --enable-cstdio=stdio
--enable-version-specific-runtime-libs
--with-gxx-include-dir=/usr/lib/gcc-lib/i686-pc-linux-gnu/3.3.4/include/g++-v3
--with-local-prefix=/usr/local --enable-shared --enable-nls
--without-included-gettext --disable-multilib --enable-__cxa_atexit
--enable-clocale=generic
Thread model: posix
gcc version 3.3.4 20040623 (Gentoo Linux 3.3.4-r1, ssp-3.3.2-2, pie-8.7.6)
"cat /proc/cpu"
processor : 0
vendor_id : AuthenticAMD
cpu family : 6
model : 3
model name : AMD Duron(tm) Processor
stepping : 1
cpu MHz : 756.798
cache size : 64 KB
fdiv_bug : no
hlt_bug : no
f00f_bug : no
coma_bug : no
fpu : yes
fpu_exception : yes
cpuid level : 1
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 sep mtrr pge mca cmov pat pse36 mmx
fxsr syscall mmxext 3dnowext 3dnow
bogomips : 1490.94
Playing with compiler optimizations I've found a "test-case" where
"-march=athlon" produces an executable that is ~18% slower than that produced
with "-march=i686".
"Commands used for compilation"
gcc -Wall -O2 -march=i686 -o test-i686 test.c
gcc -Wall -O2 -march=athlon -o test-athlon test.c
"test.c"
#define N 30000
static int A[N];
static int B[N];
int main(void)
{
int i, j, x;
for (i = 0; i < N; ++i) {
x = 0;
for (j=0; j < N; ++j)
if (A[j] < A[i] && B[j] > x)
x = A[j];
A[i] = x + 1;
}
return 0;
}
Execution time:
paolo@tux gcc_test $ time ./test-i686
real 0m6.149s
user 0m6.015s
sys 0m0.004s
paolo@tux gcc_test $ time ./test-athlon
real 0m7.270s
user 0m7.120s
sys 0m0.004s
Anoter interesting thing is that if I only do this change:
--- test.c.orig 2004-12-22 21:52:46.208140096 +0100
+++ test.c 2004-12-22 21:55:01.069638032 +0100
@@ -10,7 +10,7 @@
for (i = 0; i < N; ++i) {
x = 0;
for (j=0; j < N; ++j)
- if (A[j] < A[i] && B[j] > x)
+ if (A[j] < A[i] && A[j] > x)
x = A[j];
A[i] = x + 1;
}
The "test-athlon" version returns fast as "test-i686" one:
paolo@tux gcc_test $ time ./test-i686
real 0m6.134s
user 0m6.015s
sys 0m0.003s
paolo@tux gcc_test $ time ./test-athlon
real 0m6.128s
user 0m6.010s
sys 0m0.006s
I've tried also gcc 3.4.3 and it shows the same behaviour.
Shouldn't "-march=athlon" optimize for AMD K7 processors? ;-)
--
Summary: march=athlon can produce slower code than march=i686
Product: gcc
Version: 3.3.4
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: ornati at fastwebnet dot it
CC: gcc-bugs at gcc dot gnu dot org
GCC build triplet: i686-pc-linux-gnu
GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19133
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug target/19133] march=athlon can produce slower code than march=i686
2004-12-22 21:01 [Bug c/19133] New: march=athlon can produce slower code than march=i686 ornati at fastwebnet dot it
@ 2004-12-22 21:05 ` pinskia at gcc dot gnu dot org
2005-02-08 16:37 ` steven at gcc dot gnu dot org
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2004-12-22 21:05 UTC (permalink / raw)
To: gcc-bugs
--
What |Removed |Added
----------------------------------------------------------------------------
Component|c |target
Keywords| |missed-optimization
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19133
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug target/19133] march=athlon can produce slower code than march=i686
2004-12-22 21:01 [Bug c/19133] New: march=athlon can produce slower code than march=i686 ornati at fastwebnet dot it
2004-12-22 21:05 ` [Bug target/19133] " pinskia at gcc dot gnu dot org
@ 2005-02-08 16:37 ` steven at gcc dot gnu dot org
2005-02-08 23:18 ` ornati at fastwebnet dot it
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: steven at gcc dot gnu dot org @ 2005-02-08 16:37 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From steven at gcc dot gnu dot org 2005-02-08 10:09 -------
-march=athlon should optimize for the K7 yes. What you probably run into
is a simple backend problem where the code generated for the K7 can, for
whatever reason, not be optimized as well as the i686 code.
Can you try mainline and see what happens there? I think very few people
think this is important enough to fix for already-released compilers. But
if the problem exists on mainline as well, we can look into it.
--
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Ever Confirmed| |1
Last reconfirmed|0000-00-00 00:00:00 |2005-02-08 10:09:23
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19133
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug target/19133] march=athlon can produce slower code than march=i686
2004-12-22 21:01 [Bug c/19133] New: march=athlon can produce slower code than march=i686 ornati at fastwebnet dot it
2004-12-22 21:05 ` [Bug target/19133] " pinskia at gcc dot gnu dot org
2005-02-08 16:37 ` steven at gcc dot gnu dot org
@ 2005-02-08 23:18 ` ornati at fastwebnet dot it
2005-05-07 13:54 ` steven at gcc dot gnu dot org
2005-05-07 14:04 ` ornati at fastwebnet dot it
4 siblings, 0 replies; 6+ messages in thread
From: ornati at fastwebnet dot it @ 2005-02-08 23:18 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From ornati at fastwebnet dot it 2005-02-08 16:13 -------
gcc -v
Using built-in specs.
Configured with:
/var/tmp/portage/gcc-4.0.0_alpha20050130/work/gcc-4.0-20050130/configure
--enable-version-specific-runtime-libs --prefix=/usr
--bindir=/usr/i686-pc-linux-gnu/gcc-bin/4.0.0
--includedir=/usr/lib/gcc/i686-pc-linux-gnu/4.0.0/include
--datadir=/usr/share/gcc-data/i686-pc-linux-gnu/4.0.0
--mandir=/usr/share/gcc-data/i686-pc-linux-gnu/4.0.0/man
--infodir=/usr/share/gcc-data/i686-pc-linux-gnu/4.0.0/info
--with-gxx-include-dir=/usr/lib/gcc/i686-pc-linux-gnu/4.0.0/include/g++-v4
--host=i686-pc-linux-gnu --disable-altivec --enable-nls
--without-included-gettext --enable-__cxa_atexit --enable-clocale=gnu
--with-system-zlib --disable-checking --disable-werror
--disable-libunwind-exceptions --enable-shared --enable-threads=posix
--disable-multilib --disable-libgcj --enable-languages=c,c++
Thread model: posix
gcc version 4.0.0 alpha20050130 (Gentoo Linux 4.0.0_alpha20050130)
paolo@tux gcc_test $ time ./test-i686
real 0m8.539s
user 0m8.376s
sys 0m0.001s
paolo@tux gcc_test $ time ./test-athlon
real 0m6.168s
user 0m6.031s
sys 0m0.005s
As the numbers show, the problem go away for "-march=athlon"... but now
"-march=i686" version is MUCH slower than before (with GCC 3.3.x).
Seems like I've found a very strange test-case...
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19133
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug target/19133] march=athlon can produce slower code than march=i686
2004-12-22 21:01 [Bug c/19133] New: march=athlon can produce slower code than march=i686 ornati at fastwebnet dot it
` (2 preceding siblings ...)
2005-02-08 23:18 ` ornati at fastwebnet dot it
@ 2005-05-07 13:54 ` steven at gcc dot gnu dot org
2005-05-07 14:04 ` ornati at fastwebnet dot it
4 siblings, 0 replies; 6+ messages in thread
From: steven at gcc dot gnu dot org @ 2005-05-07 13:54 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From steven at gcc dot gnu dot org 2005-05-07 13:54 -------
Looks like random instruction selection weirdness.
Not much can be done about this.
--
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution| |WONTFIX
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19133
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug target/19133] march=athlon can produce slower code than march=i686
2004-12-22 21:01 [Bug c/19133] New: march=athlon can produce slower code than march=i686 ornati at fastwebnet dot it
` (3 preceding siblings ...)
2005-05-07 13:54 ` steven at gcc dot gnu dot org
@ 2005-05-07 14:04 ` ornati at fastwebnet dot it
4 siblings, 0 replies; 6+ messages in thread
From: ornati at fastwebnet dot it @ 2005-05-07 14:04 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From ornati at fastwebnet dot it 2005-05-07 14:04 -------
ok
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19133
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2005-05-07 14:04 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2004-12-22 21:01 [Bug c/19133] New: march=athlon can produce slower code than march=i686 ornati at fastwebnet dot it
2004-12-22 21:05 ` [Bug target/19133] " pinskia at gcc dot gnu dot org
2005-02-08 16:37 ` steven at gcc dot gnu dot org
2005-02-08 23:18 ` ornati at fastwebnet dot it
2005-05-07 13:54 ` steven at gcc dot gnu dot org
2005-05-07 14:04 ` ornati at fastwebnet dot it
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