Michael Meissner wrote:
GCC 4.2 switched the default tuning to -mtune=generic which is a compromise
between the current Intel and AMD systems, each of which have different tuning
parameters. Obviously it is a balancing act to get the right compromise, and
sometimes the generic tuning is wrong.
Also, is there a way to *automatically* get the best march value for
the local machine? In my case, jobs run on various machines (they're
submitted by SGE): they generate C code, compile it locally and run
it. I don't even have a direct ssh access to some of these machines.
-march=native was added in GCC 4.2 will probe the system and set the
appropriate tuning defaults. Some Linux vendors have ported the -march=native
support back to their 4.1 compilers.
There isn't a way for an automatic procedure to guess whether you want the
better numerical consistency and some newer instructions of-march=native,
or the often better performance (on Intel 32-bit mode) of -march=pentium-m.
