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Dominique_71
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Joined: 17 Aug 2005
Posts: 1896
Location: Switzerland (Romandie)
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 Posted: Wed Aug 30, 2006 1:40 pm Post subject: |
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Thank you for the informations on this thread.
I have now the following flags: | Code: | CFLAGS="-O3 -march=pentium4 -pipe -fomit-frame-pointer -fforce-addr -fno-ident -ftracer"
CXXFLAGS="${CFLAGS}"
LDFLAGS="-Wl,-O1 -Wl,--sort-common" |
That's with gcc 3.4.6. The result is a very stable system, the -fforce-addr is doing good with -O3, but the problem I get with it is at the resulting code is not faster as with -O2 alone, and still is bigger and take more time to compile. So I will get back to -O2, because I just don't have the time to test all my program to know when it is safe to use -O3 without -fforce-addr, and when I must add -fforce-addr. I done the test with the nec2 antenna simulation software (not in portage), and -O2 is just better because it will compile faster and load faster as the same program compiled with -O3 -fforce-addr.
The main uses for my box are audio and electronic simulation. I am planing to change my flags at the same time at I will upgrade to gcc4.
It is a few new flags with gcc, but it is hard to find reliable information about what they are doing. As exemple, about -ftree-vectorize, we can read in the gcc4.1 manual: | Quote: | -ftree-vectorize
Perform loop vectorization on trees. |
It is not much. This option is not in any -O flag, and it is no warning of any kind. I thing at it will be safe and at it can be a good thing to have on a system that use audio and scientific program. I am thinking to use something as | Code: | CFLAGS="-O2 -march=pentium4 -pipe -fweb -ftree-vectorize -fomit-frame-pointer -momit-leaf-frame-pointer -fno-ident"
CXXFLAGS="${CFLAGS}"
LDFLAGS="-Wl,-O1 -Wl,--sort-common" |
Will it be safe as main use flags?
I removed -fvisibility-inlines-hidden from my CXXFLAGS (I can confirm at it break things.). Will it be safe to add it with gcc4.1, or will it be the same problems as with gcc3.4? What about -ftracer and gcc4.1?
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Eduard Munteanu
n00b
Joined: 06 Sep 2006
Posts: 20
Location: Bucuresti, Romania
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| Posted: Sun Sep 10, 2006 11:07 pm Post subject: |
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moocha, using -momit-leaf-frame-pointer is useless with -fomit-frame-pointer:
| man gcc (4.1.1-r1) wrote: | -momit-leaf-frame-pointer
Don't keep the frame pointer in a register for leaf functions.
This avoids the instructions to save, set up and restore frame
pointers and makes an extra register available in leaf functions.
The option -fomit-frame-pointer removes the frame pointer for all
functions which might make debugging harder. |
Also, -march implies -mtune, so there is no reason to use both. |
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Dominique_71
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Joined: 17 Aug 2005
Posts: 1896
Location: Switzerland (Romandie)
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| Posted: Mon Sep 11, 2006 1:10 pm Post subject: |
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I try the flag as in my first messages, but the result was an unusable system. Only xdm and fluxbox was starting, but a lot of other program was just crashing: fluxconf, fluxmenu, gdm, xfce and many more. So I went back to safer flags.
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rhill
Retired Dev
Joined: 22 Oct 2004
Posts: 1629
Location: sk.ca
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| Posted: Tue Sep 12, 2006 1:31 am Post subject: |
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-fforce-addr - not a good idea with GCC 4 and x86. x86 already has a horribly limited number of registers, and using more will just increase register pressure, resulting in poorer code. packages that use a lot of hand-made assembly, (eg. ffmpeg, mplayer, transcode) can fail with this flag. same with -frename-registers and -fforce-mem
-ftree-vectorize - still buggy with GCC 4.1 and not improving in 4.2. there's a large number of vectorizer patches that should have gone into 4.2 but were deferred til 4.3 due to lack of proper review. =/ http://tinyurl.com/z79jz
-ftree-loop-linear - ditto, but without the forthcoming patches. don't use this unless you like internal compiler errors. http://tinyurl.com/msfnf
-momit-leaf-frame-pointer - sounds good, but i know there's more than a couple ebuilds that have to filter it to build. (eg. xine-lib, ffmpeg)
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Dr.Dran
l33t
Joined: 08 Oct 2004
Posts: 766
Location: Imola - Italy
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| Posted: Tue Sep 12, 2006 4:49 pm Post subject: |
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Hi at all!!!
@dirtyepic I will show you my CFLAGS configuration and LDFLAG (I have a VIA C7 Easter core):
| Code: | CFLAGS="-O2 -march=i686 -mmmx -msse -msse2 -msse3 -fomit-frame-pointer -momit-leaf-frame-pointer -fno-ident -pipe"
CXXFLAGS="${CFLAGS}"
LDFLAGS="-Wl,-O1 -Wl,--as-needed" |
Does that configuration look good for the system? Fon now I haven't notice any serious problem...
Best regards
Franco Tampieri
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