Re: [Qemu-devel] [PATCH] Updated Sparc support

["David S. Miller" <davem@redhat.com>]

   From: Johan Rydberg <jrydberg@night.trouble.net>
   Date: Thu, 15 May 2003 22:17:24 +0200

   Using global registers for commonly used variables such as the CPU
   structure and current virtual program counter will increase the
   performance with a magnitude I guess.
   
   So, if I understand you correctly, everything should work pretty good
   i you use -fflat and stay away from the input registers?  (I have no
   need for the -fno-delay-slot flag)
   
-mflat SUCKS, it generates the worst code possible.

Also, if you're going to use global register, be forewarned that
if you call into libc you risk them being clobbered.  Sparc-linux
libc clobbers just about every global register in some piece of
assembly somewhere.

There are also very strict rules about which global register an
application can use in this fashion.  Please refer to the standards
documents about exactly which these are (they are different for 32-bit
and 64-bit sparc) and no I don't have time to discuss this further
nor point you at where to get these documents.:-)