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On Fri, 2006-07-07 at 16:03 +0200, Diego 'Flameeyes' Pettenò wrote: |
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> On Friday 07 July 2006 15:53, Martin Schlemmer wrote: |
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> > Check Chris Gianelloni's mail just now. For some compilers with some |
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> > -march's on x86 it did not explicitly turn on some features (or maybe |
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> > not to such a high extend). |
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> Uh no, I think he meant that for some borderline processors there's not |
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> a -march value, like for Athlon64 Revision D, that has sse3 support. In those |
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> cases you have to use -msse3 or whatever else to tell the compiler what to |
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> generate. |
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> |
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> > So where say CFLAGS="-march=pentium3" would |
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> > work, CFLAGS="-march=pentium3 -msse" would fail to build, or generate |
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> > bad code (segfaulting binaries). |
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> This might have been true with _older_ GCC, but all the series 3.3, 3.4, 4.0 |
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> and 4.1 behaves correctly: -march=pentium3 implies -msse without doubt. |
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> |
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> What you might incorrectly remember is -mfpmath=sse that is totally another |
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> thing, and dies usually on bad code anyway, and it's enabled by default on |
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> 64-bit CPUs just because on there the 80-bit limit for doubles is not |
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> pertinent anymore. |
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> |
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As I pointed out on irc (to clarify), its still an issue even with |
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gcc-3.4.6. Its just well enough filtered, and as Mike pointed out, they |
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'fixed' it in 3.4.5 via specs, and 3.4.6 by backporting patches from |
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4.0.1 I think. |
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> I might seem an idiot, but I have enough experience to know what I'm talking |
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> about. Seems instead that other people confuse SEGFAULT with SIGILL and -msse |
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> with -mfpmath=sse (or simply remember just what happened with GCC 3.2). |
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> |
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I did not imply this as far I know, and if it seemed that way, I can |
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only say that I assumed that newer guys had the advantage of most |
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ebuilds filtering or -mno-sse/whatever for known broken stuff (I know |
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xorg was one with a few workarounds, also mozilla, etc at at some |
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stage), so would not have noticed if sse/whatever broke something. |
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That, and not being on the toolchain list you might not be familiar with |
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the extend of the issue, with the fact that its different issues with |
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different versions depending besides that on if its a i586, k6, p2, p3 |
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or p4, etc. |
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> A little note here: tools improve. GCC 2.95 was a joke, GCC 3.0, 3.1 were |
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> almost unusable, 3.2 started to be usable but full of problems, 3.3/3.4 |
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> series improved, drastically. |
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> Stuff like visibility is badly broken up to 4.0, but works fine on 4.1. You |
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> cannot think that a flag or a support will always be broken because a release |
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> had it broken, you have to watch what you're doing to do it correctly. |
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> |
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I'd say only 4.0.1 and upwards really solved most of those issues, |
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especially the long comming sse one. |
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-- |
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Martin Schlemmer |
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