On 29 Sep 2003, at 12:10 pm, Ulrich Rhein wrote:
4. What's the deal with the sse2 on the P4? I vaguely remember on the
mailing lists there was something bad going on with either sse2 or
-march=pentium4 and some version of gcc... Question: Will it be safe for me
to specify -march=pentium4 in my CFLAGS?
gcc doesn't use SIMD instructions (except in very rare cases), because it is hard for a compiler to use them. Additionally, gcc doesn't generate much faster (just bigger) code when compiling with -march=..., if it does generate different code at all. There is usually no significiant performance gain with it.
Why is Gentoo's ability to set CFLAGS optimisations in make.conf so widely touted, then..?
Surely if what you say is true, then this is a redundant feature of portage.
I was thinking of installing Portage on my Mac; if what you say is true, then I guess I'm as well off with Fink..?
I was under the impression that it depended on what the application actually does. Any programs that do any kind of video or multimedia can typically be greatly speeded up by a -mmmx or -m3dnow which would be included by default for any -march=xxx where the processor supports it.
-- Andrew Gaffney
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