register allocation for SPARC

[laurent]

Hello,

I get a processor SPARC-V8  dedicated to embedded application. So far I
have used gcc-3.4.4 version with option "-mflat" to limit register file
to 32 registers (register window model was de-activated).

Now I have to upgrade GCC version (to get new optimisations), but the
"-mflat" option is no more supported in newer GCC options.

Is there a way to get "-mflat" option on new GCC version? 
If the answer is "no", is there a trick to never allocate some registers
when we use the register window model?  My scope would be to remove all
%l3 to %l7 registers for instance in order to save silicon area.

I need your help, thanks,

  Laurent POCHE