GCC4 and CFLAGS

Guinpen · Guru Joined: 08 Dec 2004 Posts: 393

I wonder why I didn't find this already asked on the forum, but hey, here it comes: Will the following happily fuctioning (under GCC 3.4.4) CFLAGS work on GCC 4.0.2 which I want to try out? What about 4.1.0 (beta)? Hardware is Pentium-M 1.3 Banias, 512 RAM.

Gnufsh · Guru Joined: 28 Dec 2002 Posts: 400 Location: Portland, OR

Yes., but -momit-leaf-pointer is implied by -fomit-frame-pointer and possibly -O2, so you don't really need it. And people generally advise against -ffast-math. I used -ffast-math for a while, now I don't. I didn't have that many problems with it because most packages that it breaks filter it out. Of course, these are generally the ones that would see the greatest speed-up.

Guinpen · Guru Joined: 08 Dec 2004 Posts: 393

Thank you, I have taken your suggestions in mind and removed the 2 flags.

nbvcxz · Guru Joined: 02 Sep 2005 Posts: 379 Location: Kraków / PL

My suggestion is add -ftree-vectorize -fno-ident -s to CFLAGS and CXXFLAGS="${CFLAGS} -fvisibility-inlines-hidden -fno-enforce-eh-specs". You can also remove some debugging code by adding -DNDEBUG -DG_DISABLE_ASSERT -DNO_DEBUG but be carefull - eg. gimp don't like it. Pls have a look at https://forums.gentoo.org/viewtopic-t-333123.html
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Guinpen · Guru Joined: 08 Dec 2004 Posts: 393

Thanks, although I definitely don't need more crazy optimization over what I have.. it's fast enough, and quite stable like this. I was more worried about GCC4 being broken for my existing flags, rather than adding new ones.

BTW, would -Os instead of -O2 produce substantial decrease in memory requirements for applications, or am I dreaming?

Gnufsh · Guru Joined: 28 Dec 2002 Posts: 400 Location: Portland, OR

I don't think it would be substantial. IMHO, you're better off with -O2, performance-wise.

cheater1034 · Veteran Joined: 09 Sep 2004 Posts: 1558

I am also looking for a stable and optmized setup for GCC 4.x

so far building up, I was considering.

nbvcxz · Guru Joined: 02 Sep 2005 Posts: 379 Location: Kraków / PL

Au contraire Gnufsh. Because of my rather old computer with Gentoo installed and only 124 Mb ram I use (which works great):

cheater1034 · Veteran Joined: 09 Sep 2004 Posts: 1558

nxsty · Veteran Joined: 23 Jun 2004 Posts: 1556 Location: .se

I wouldn't recomend using the vectorizer in gcc 4.0. It's still suboptimal and usually only decreases performance. It'll be much better in 4.1 and 4.2.

nbvcxz · Guru Joined: 02 Sep 2005 Posts: 379 Location: Kraków / PL

enderandrew · l33t Joined: 25 Oct 2005 Posts: 731

luisfelipe · Guru Joined: 09 Apr 2005 Posts: 377

Just a quick note : with gcc 4.1 at least, some packages require -ffriend-injection in order to compile. Also, my system still has something
like 15 packages that don't compile with it yet, but they are mostly small stuff.
I didn't notice any significant speed increase after upgrading from gcc 3.x .

yoshi314 · l33t Joined: 30 Dec 2004 Posts: 850 Location: PL

i believe i had. but it could just be because i installed newer packages since i installed everything from scratch ( accidental mkfs on /home and you feel free to experiment :/ ) but i think that at least gcc4 works faster than gcc3, as big packages take less time to build. (there is some improvement with glibc, for example)

i use 4.0.2 with pentium4-based celeron willamette 1.7ghz (it's said to be dog slow, perhaps it is) and 768mb ram

luisfelipe · Guru Joined: 09 Apr 2005 Posts: 377

transcode compiles here. And you are indeed correct about gcc4 being faster at compiling. When I said that I didn't notice
any performance increase, I meant system-wise.

Tiger683 · Posted: Wed Dec 14, 2005 2:24 pm Post subject:

insane LDFLAGS don't break more packages under gcc-4 than under gcc-3, that's a fact.
Actually, only thing that might mess up something is --as-needed, but mostly stuff that can't take it simply doesn't compile, so you know what's up
before runtime.

The masked version of transcode in portage (1.X.X) builds with gcc-4.1

Kernels built with gcc-4.X are noticeably slower than built with gcc-3.4
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nxsty · Veteran Joined: 23 Jun 2004 Posts: 1556 Location: .se

cheater1034 · Veteran Joined: 09 Sep 2004 Posts: 1558

nxsty · Veteran Joined: 23 Jun 2004 Posts: 1556 Location: .se

Tiger683 · Posted: Wed Dec 14, 2005 7:41 pm Post subject:

cheater1034 · Veteran Joined: 09 Sep 2004 Posts: 1558

mpalencia · n00b Joined: 16 Feb 2005 Posts: 51 Location: Colombia

My current system is compiled from scratch using gcc 4.0.2-20051110 (overlay) and nxstys overlay which adds support for -Bdirect.
these are my LDFLAGS:
LDFLAGS="-Wl,-O1 -Wl,-Bdirect -Wl,-z,now"
Of course, -Bdirect is still experimental, although I have not had any problems with it.
The recommended "stable" that will probably not break anything is -Wl,-O1
I use -z,now because it loads all the libraries used by an application, which incresases load time but improves performance and stabilty (or so I read)
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enderandrew · l33t Joined: 25 Oct 2005 Posts: 731

cheater1034 · Veteran Joined: 09 Sep 2004 Posts: 1558

Well

I dont know what to say.
(1) - The Setup, LDFLAGS="-W1,-O1", did not work (maybe I did it wrong :?:

)
(2) - Attempting stability, Im staying away

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mpalencia · n00b Joined: 16 Feb 2005 Posts: 51 Location: Colombia