Optimal compile flags for ultra2 & power2

[David S. Miller]

   Date: Tue, 22 Sep 1998 12:50:57 EDT
   From: John Carr <jfc@MIT.EDU>

   >    I was wondering what flags people use for best FP performance on these -
   > 
   >    a) Sun ultra2
   > 
   > -O2 -mtune=ultrasparc -fcall-used-g4 -fcall-used-g5 -fcall-used-g7

   %g7 is used by the Solaris thread library, so don't use -fcall-used-g7
   in multithreaded programs (which includes any program using XIL in
   Solaris 2.6).

Right, and if it is non-threaded you can add -fcall-used-g6 as well.
Thanks for pointing this out.

   -mcpu=ultrasparc will enable the V9 floating point instructions and
   should improve performance on an Ultra; code compiled with this switch
   will not run on older SPARCs.

I get enough egcs-1.1 compiler crashes and bad code-gen reports about
-mcpu=ultrasparc that I fail to recommend it any more.  Hopefully I
can stabilize this in the main line soon...

Later,
David S. Miller
davem@dm.cobaltmicro.com