Re: gcc -mxxx=???

[Peter Cordes <peter@llama.nslug.ns.ca>]

On Fri, Jun 15, 2001 at 01:56:45PM +0200, Michel D?nzer wrote:
> 
> 
> My $CFLAGS looks like this: -pipe -O2 -Wall -mcpu=750 -fstrict-aliasing
> 
> It's not entirely clear from the gcc docs if code generated this way runs on
> older CPUs than G3s though. Should I rather use -mtune=750? What would be
> optimal for -mcpu for all CPUs we support?
> 
> 
> I wonder if anyone running on something like 604 or 603 has had strange
> problems like illegal instructions with packages I built?

 gcc for IA32 uses -march=... to control what instructions it is
allowed to use, and what arch to tune for.  You can override the
tuning target with -mcpu=....  Specifying -mcpu=... without -march
still generates code that will run on a 386.

 I don't know how things are for PPC, but unless things are way
different, -mcpu=... shouldn't change what instructions gcc restricts
itself to.  (i.e. -mcpu shouldn't make it run on any less machines
than it would before.  Things aren't quite as simple as IA32, because
I don't remember if the default instruction set is actually the subset
that will work on _all_ ppc machines.)

-- 
#define X(x,y) x##y
Peter Cordes ;  e-mail: X(peter@llama.nslug. , ns.ca)

"The gods confound the man who first found out how to distinguish the hours!
 Confound him, too, who in this place set up a sundial, to cut and hack
 my day so wretchedly into small pieces!" -- Plautus, 200 BCE