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From: Bozhan Boiadzhiev <[EMAIL PROTECTED]>
To: Debian Bug Tracking System <[EMAIL PROTECTED]>
Subject: gcc-3.3: optimization -O2 is worst than -O1
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Date: Sat, 22 Jan 2005 16:26:49 +0200
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Package: gcc-3.3
Version: 1:3.3.5-5
Severity: normal
I found this page
http://www.network-theory.co.uk/docs/gccintro/gccintro_43.html
and i diceide to try it becouse i was curios of
optimizations.
And the results are little strange.
I have two more configuration on woody and one redhat9
with default packages installed and updated.
Here are results:
Debian Testing:
Linux version 2.6.8-2-686 ([EMAIL PROTECTED]) (gcc version
3.3.5 (Debian 1:3.3.5-5)) #1 Sat Jan 8 16:50:08 EST 200
5
carredas:/home/edmon# cat /proc/cpuinfo
processor : 0
vendor_id : GenuineIntel
cpu family : 15
model : 2
model name : Intel(R) Celeron(R) CPU 2.00GHz
stepping : 9
cpu MHz : 1991.977
cache size : 128 KB
fdiv_bug : no
hlt_bug : no
f00f_bug : no
coma_bug : no
fpu : yes
fpu_exception : yes
cpuid level : 2
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge
mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe cid
bogomips : 3948.54
carredas:/home/edmon# gcc -Wall -O0 test.c -lm
carredas:/home/edmon# time ./a.out
sum = 4e+38
real 0m8.381s
user 0m8.374s
sys 0m0.004s
carredas:/home/edmon# time ./a.out
sum = 4e+38
real 0m8.409s
user 0m8.360s
sys 0m0.007s
carredas:/home/edmon# time ./a.out
sum = 4e+38
real 0m8.381s
user 0m8.378s
sys 0m0.004s
carredas:/home/edmon# time ./a.out
sum = 4e+38
real 0m8.339s
user 0m8.333s
sys 0m0.001s
carredas:/home/edmon# gcc -Wall -O1 test.c -lm
carredas:/home/edmon# time ./a.out
sum = 4e+38
real 0m5.644s
user 0m5.641s
sys 0m0.002s
carredas:/home/edmon# time ./a.out
sum = 4e+38
real 0m5.640s
user 0m5.638s
sys 0m0.002s
carredas:/home/edmon# time ./a.out
sum = 4e+38
real 0m5.647s
user 0m5.646s
sys 0m0.001s
carredas:/home/edmon# time ./a.out
sum = 4e+38
real 0m5.651s
user 0m5.649s
sys 0m0.000s
carredas:/home/edmon# gcc -Wall -O2 test.c -lm
carredas:/home/edmon# time ./a.out
sum = 4e+38
real 0m5.726s
user 0m5.722s
sys 0m0.002s
carredas:/home/edmon# time ./a.out
sum = 4e+38
real 0m5.731s
user 0m5.723s
sys 0m0.003s
carredas:/home/edmon# time ./a.out
sum = 4e+38
real 0m5.792s
user 0m5.731s
sys 0m0.008s
carredas:/home/edmon# gcc -Wall -O3 test.c -lm
carredas:/home/edmon# time ./a.out
sum = 4e+38
real 0m4.218s
user 0m4.215s
sys 0m0.003s
carredas:/home/edmon# time ./a.out
sum = 4e+38
real 0m4.186s
user 0m4.182s
sys 0m0.003s
carredas:/home/edmon# time ./a.out
sum = 4e+38
real 0m4.189s
user 0m4.187s
sys 0m0.001s
Debian Woody:
Linux version 2.2.19 ([EMAIL PROTECTED]) (gcc version 2.7.2.3) #1 Sat
Jun 9 13:04:06 EST 2001
mail:~# cat /proc/cpuinfo
processor : 0
vendor_id : GenuineIntel
cpu family : 5
model : 4
model name : Pentium MMX
stepping : 3
cpu MHz : 171.309
fdiv_bug : no
hlt_bug : no
sep_bug : no
f00f_bug : yes
coma_bug : no
fpu : yes
fpu_exception : yes
cpuid level : 1
wp : yes
flags : fpu vme de pse tsc msr mce cx8 mmx
bogomips : 341.60
mail:~# gcc -Wall -O0 test.c -lm
mail:~# time ./a.out
sum = 4e+38
real 1m18.922s
user 1m13.630s
sys 0m0.010s
mail:~# gcc -Wall -O1 test.c -lm
mail:~# time ./a.out
sum = 4e+38
real 0m46.862s
user 0m45.240s
sys 0m0.030s
mail:~# gcc -Wall -O2 test.c -lm
mail:~# time ./a.out
sum = 4e+38
real 0m45.667s
user 0m44.320s
sys 0m0.010s
mail:~# gcc -Wall -O3 test.c -lm
mail:~# time ./a.out
sum = 4e+38
real 0m22.718s
user 0m21.730s
sys 0m0.010s
And REd Hat 9:
Linux version 2.4.20-8smp ([EMAIL PROTECTED]) (gcc
version 3.2.2 20030222 (Red Hat Linux 3.2.2-5)) #1 SMP Thu M
ar 13 17:45:54 EST 2003
[EMAIL PROTECTED] root]# cat /proc/cpuinfo
processor : 0
vendor_id : GenuineIntel
cpu family : 15
model : 2
model name : Intel(R) Pentium(R) 4 CPU 2.40GHz
stepping : 9
cpu MHz : 2411.645
cache size : 512 KB
physical id : 0
siblings : 2
fdiv_bug : no
hlt_bug : no
f00f_bug : no
coma_bug : no
fpu : yes
fpu_exception : yes
cpuid level : 2
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge
mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm
bogomips : 4810.34
processor : 1
vendor_id : GenuineIntel
cpu family : 15
model : 2
model name : Intel(R) Pentium(R) 4 CPU 2.40GHz
stepping : 9
cpu MHz : 2411.645
cache size : 512 KB
physical id : 0
siblings : 2
fdiv_bug : no
hlt_bug : no
f00f_bug : no
coma_bug : no
fpu : yes
fpu_exception : yes
cpuid level : 2
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge
mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm
bogomips : 4810.34
[EMAIL PROTECTED] root]# gcc -Wall -O0 test.c -lm
[EMAIL PROTECTED] root]# time ./a.out
sum = 4e+38
real 0m10.779s
user 0m10.780s
sys 0m0.000s
[EMAIL PROTECTED] root]# gcc -Wall -O1 test.c -lm
[EMAIL PROTECTED] root]# time ./a.out
sum = 4e+38
real 0m5.161s
user 0m5.140s
sys 0m0.000s
[EMAIL PROTECTED] root]# gcc -Wall -O2 test.c -lm
[EMAIL PROTECTED] root]# time ./a.out
sum = 4e+38
real 0m5.123s
user 0m5.110s
sys 0m0.000s
[EMAIL PROTECTED] root]# gcc -Wall -O3 test.c -lm
[EMAIL PROTECTED] root]# time ./a.out
sum = 4e+38
real 0m3.245s
user 0m3.240s
sys 0m0.000s
As you see result for testing for -O2 are worst than -O1 :(
I am not very in compiling and so on .
Maybe i am missing something.
It will be good if bigger optimization gives better results:)))
:)
-- System Information:
Debian Release: 3.1
APT prefers testing
APT policy: (500, 'testing')
Architecture: i386 (i686)
Kernel: Linux 2.6.8-2-686
Locale: LANG=C, LC_CTYPE=C (charmap=ANSI_X3.4-1968)
Versions of packages gcc-3.3 depends on:
ii binutils 2.15-5 The GNU assembler, linker and bina
ii cpp-3.3 1:3.3.5-5 The GNU C preprocessor
ii gcc-3.3-base 1:3.3.5-5 The GNU Compiler Collection (base
ii libc6 2.3.2.ds1-20 GNU C Library: Shared libraries an
ii libgcc1 1:3.4.3-6 GCC support library
-- no debconf information
---------------------------------------
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To: [EMAIL PROTECTED]
Subject: Re: Bug#291693: gcc-3.3: optimization -O2 is worst than -O1
References: <[EMAIL PROTECTED]>
From: Falk Hueffner <[EMAIL PROTECTED]>
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Date: Sat, 22 Jan 2005 16:51:43 +0100
In-Reply-To: <[EMAIL PROTECTED]> (Bozhan
Boiadzhiev's message of "Sat, 22 Jan 2005 16:26:49 +0200")
Message-ID: <[EMAIL PROTECTED]>
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Bozhan Boiadzhiev <[EMAIL PROTECTED]> writes:
> carredas:/home/edmon# gcc -Wall -O1 test.c -lm
> carredas:/home/edmon# time ./a.out
> sum = 4e+38
>
> real 0m5.644s
> user 0m5.641s
> sys 0m0.002s
> carredas:/home/edmon# gcc -Wall -O2 test.c -lm
> carredas:/home/edmon# time ./a.out
> sum = 4e+38
>
> real 0m5.726s
> user 0m5.722s
> sys 0m0.002s
>
> As you see result for testing for -O2 are worst than -O1 :(
But only marginally, and on a completely artificial test case, and I
can't reproduce it on a different CPU (Athlon64). So I don't think
this is worth examining.
--
Falk
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