Re: [gentoo-dev] make.conf optimization flags for k6, athlon

[Thomas Beaudry <k8la@arrl.net>]

> > A few comments I've been meaning to make.
> >
> > 1.  According to the GCC documentation you shouldn't be using 
-m<processor>
> > any more. It's been depreciated in favor of -mcpu<processor>.
> I know that. The mpentium etc. flags wre in the originl make.conf, the 
things
> I added were -march=x -mcpu=x. I'll change mpentium for march=pentium if 
I
> haven't already.

Just making an observation of what I've seen to date.  Haven't seen your 
additions yet.  In fact, I just downloaded them.

> >
> > 2.  You don't need to use -mcpu usually with -march as -march sets -mcpu
> > for you.  I say usually 'cause there's an AMD processor (can't remember
> > which) that uses a different instruction set than the default set by the
> > -march it uses.
> I think you're wrong. If I say march=i486 mcpu=i586 this means the binary
> will run on any 486 or better, but is optimized for the 586.

You're correct.  I had the nagging feeling there was a second exception 
but decided I was crazy after thinking about it for a few seconds.  
Didn't have the time then to look it up.


> >
> > 3.  The usage of processor names has been depreciated as well.  Should
> > use i586, etc. instead.
> For intel processors maybe. However AMD's k6, though a 586, is better 
than a
> Pentium, and the Athlon, though a 686, is better than a Pentium3.

> Although it really would be better if gcc allowed for flags of 
instruction
> sets etc. so that you could define your 'custom processor' by saying, use
> MMX+3DNow!2+sse. Than we'd know exactly what optimization it was doing.

Now arguments there.  It really peaves me that it won't use the MMX 
extensions on my Pentium 167 +MMX machine.