[geeks] AMD64 compiler flags

[Francisco Javier Mesa-Martinez]

On Sat, 6 Nov 2004 10:56:19 -0500
  Charles Shannon Hendrix <shannon at widomaker.com> wrote:
> Tue, 26 Oct 2004 @ 15:53 -0700, Francisco Javier 
>Mesa-Martinez said:
> 
>> the math flags for mmx and sse are useless, as is 
>>-march=k8 depending 
>> on which gcc version you are using. 
>>                                  
> 
> Why do you say mmx and sse are useless? 

In the AMD64 target at this point they're useless... If 
you are targetting a 32bit x86 like P4 et al, I believe 
that yes indeed you can get some nice code out of those 
flags. Sorry if I wasn't specific about that.

> 
>> If your gcc is pure 64bit, then you also don't need the 
>>-m64 flag, if
>> you have a "generic" or are crosscrompile then use the 
>>-m64 to force
>> 64bit execs. Also do not use -mtune it gave us a few 
>>headaches
> 
> I thought -mtune was implied by -march...

I believe it is being deprecated in 3.4.x, as far as my 
experience is concerned we have had indeed some troubles 
with that flag.

> 
> What I'm curious about is how the system managed to run 
>64-bit execs on
> a 32-bit OS.

Huh? Never claimed to have done such thing, you can 
however crosscompile from a 32bit machine and generate 
64bit targets that can be run in a 64bit machine.


> No, I'm running a 32-bit kernel and C library.
> 
> I thought about playing with a 64-bit BSD or Linux 
>distribution, but
> haven't really researched it much yet.

Then you need to get a 64bit distro and kernel ASAP, the 
speed difference is SIGNIFICANT at least in our 
experience. :) At least most of the machines I am using 
for simulation are Xeons with the 64bit extensions and we 
are getting some very nice performance out them with 64bit 
2.4 kernels.