Re: [gentoo-dev] Re: [RFC] CFLAGS paragraph for the GWN
Duncan wrote: Could you point me at some info on this one (-ftree-vectorize)? It came up on the amd64 list a week or so ago, when someone asked what I thought of it and why I didn't have it in my cflags (which I had just explained). I said I didn't know enough about it to make a case either way, and as such, didn't choose to use it. However, after a bit of discussion, I decided to add it to my cflags on a very experimental basis. I haven't experienced any issues with it, but then I haven't done any major compiling since then either, only the routine updates. If I had rather more info on it, therefore, particularly on why it might break stuff, I'd be able to pass it on, telling the list and in particular the guy that asked, why it's NOT a good thing to use. Thus, point me at it, if you got it. Even something as simple as a list of bugs traced to it would be useful as something I could point at, if that's what you are basing your remark on. I can't give you reasons, but I can tell you it totally broke my x86 system a while back. Thanks, Donnie -- gentoo-dev@gentoo.org mailing list
Re: [gentoo-dev] Re: [RFC] CFLAGS paragraph for the GWN
On Sunday 01 October 2006 18:49, Donnie Berkholz wrote: I can't give you reasons, but I can tell you it totally broke my x86 system a while back. -ftree-vectorize on x86 and PowerPC is known to create broken executables (when it comes to actually create the executable). I'm using it on AMD64 fine since 4.0 pre-releases though (suggested for the daredevils by Halcy0n iirc), and never had problems with it. Most likely this is due either to the usual limitations of x86 (registers, PIC, 387 fpmath), or to not be able to ensure the availability of extra instructions on x86. -- Diego Flameeyes Pettenò - http://farragut.flameeyes.is-a-geek.org/ Gentoo/Alt lead, Gentoo/FreeBSD, Video, AMD64, Sound, PAM, KDE pgpnzY9hTxsVG.pgp Description: PGP signature
Re: [gentoo-dev] Re: [RFC] CFLAGS paragraph for the GWN
On Sun, 1 Oct 2006 11:23:37 + (UTC) Duncan [EMAIL PROTECTED] wrote: Ryan Hill [EMAIL PROTECTED] posted [EMAIL PROTECTED], excerpted below, on Sat, 30 Sep 2006 16:37:05 -0600: If you want flags that just break stuff with 4.1 you can include -ftree-vectorize. Could you point me at some info on this one (-ftree-vectorize)? SNIP1one -ftree-vectorize replaces the already deprecated -fentmoot, which is of course a Really Old option for GCC where all code is blown up in memory and then parsed and spit out in as many different ways as possible to ultimately come to the best most very optimised way to say the simplest things. It is wise to also use -Woverly-longwinded in this case, so all the optimisation steps are written verbosely to stderr interspersed with funny anecdotal evidence of extraneously confablucious witticisms (to stdout, naturally).[1] Kind regards, JeR [1] -fentmoot got the chop from one of the Wizards of Yore who is known by many as Saruman the Black and White Water-Loving Bird, and the rest is History. -- gentoo-dev@gentoo.org mailing list
Re: [gentoo-dev] Re: [RFC] CFLAGS paragraph for the GWN
On Sat, Sep 30, 2006 at 03:48:53PM -0600, Ryan Hill wrote: Lionel Bouton wrote: There are already good resources (http://gentoo-wiki.com/CFLAGS_matrix was mentioned to me by robbat2) but they may not be advertised enough. Most of the info on that page is wrong. The items on there that note breakages are reasonably correct. -fvisibility=hidden and -ffast-math DO cause breakages. -ftree-loop-linear likewise is broken on GCC4.1 last I checked. I'd like to propose a paragraph to the GWN editor which presents some gotchas and good references on the subject. Honestly, the only good reference is the Safe CFLAGS page. The objective here was mainly to point out some things that users are doing that are causing breakages, leading to bugs that are ultimately marked INVALID after much tracing. -- Robin Hugh Johnson E-Mail : [EMAIL PROTECTED] GnuPG FP : 11AC BA4F 4778 E3F6 E4ED F38E B27B 944E 3488 4E85 pgpQ5caJCq57I.pgp Description: PGP signature
Re: [gentoo-dev] Re: [RFC] CFLAGS paragraph for the GWN
On Sat, Sep 30, 2006 at 04:37:05PM -0600, Ryan Hill wrote: I thought he wanted flags that broke upgrading between GCC 3.4 and 4.1. tree-loop-linear wasn't in 3.4. If you want flags that just break stuff with 4.1 you can include -ftree-vectorize. Thanks. The objective here was mainly to point out some things that users are doing that are causing breakages, leading to bugs that are ultimately marked INVALID after much tracing. Like using CFLAGS not on the Safe CFLAGS page? ;) Not really. One needs to use some common sense as a developer in evaluating user CFLAGS - because there are plenty of flags that are safe, but aren't listed on that page. Several years ago, I wrote a package that was the forerunner of the 'Safe CFLAGS' page - genflags. It was close to unmaintable at the time however, so it's suffered a lot of bit-rot. With the advent of libcpuinfo, and x86info being written, it stands a much better chance of giving useful output, but that still does not supersede the common sense statement above. -- Robin Hugh Johnson E-Mail : [EMAIL PROTECTED] GnuPG FP : 11AC BA4F 4778 E3F6 E4ED F38E B27B 944E 3488 4E85 pgpbjtxaOcfz0.pgp Description: PGP signature
