[gentoo-dev] Re: CPU use flag detection

[Ryan Hill]

On Sat, 18 May 2013 12:14:35 -0700
Matt Turner <mattst88@g.o> wrote:

> > MMX2/MMXEXT still confuses me.
>
> SSE1 and /Enhanced/ 3DNow! added some extra MMX instructions. Some
> (pshufw and pmulhuw particularly) turn out to be rather useful in
> software compositing. I use them in the pixman MMX code.
>
> See http://mattst88.com/programming/asmref/ (Sorry about the broken
> search box. It works, you just don't see what you type)

Oh I am going to get a lot of use out of this.

> Set Requires = Enhanced 3DNow!. The instructions that are listed as
> 'Enhanced 3DNow! or SSE1' are what are known as MMX2 or MMXEXT.
>
> The particularly annoying thing about using them is that there's no
> -mmmx2 or -mmmxext, but turning on -msse causes illegal instructions
> to be generated for old AMD or Geode CPUs, while -m3dnow causes the
> same problems for Intel CPUs. And, there's not actually even an
> -m3dnowext flag (anymore?) anyway, so it's kind of a mess.

Ah, that explains why I always thought they were Enh 3DNow options.  Looks like
I have them spread out between MMX and Enh 3DNow in analyze-x86.  Oops.


-- 
Ryan Hill                        psn: dirtyepic_sk
   gcc-porting/toolchain/wxwidgets @ gentoo.org

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