[SPARC] Enable REE at -O2 by default in 64-bit mode

[Jeff Law]

On 11/24/2016 08:30 AM, Eric Botcazou wrote:
> Tests showed that it helps to eliminates redundant 32-to-64-bit extensions.
>
> Tested on SPARC/Solaris, applied on the mainline.
>
>
> 2016-11-24  Eric Botcazou  <ebotcazou@adacore.com>
>
> 	* common/config/sparc/sparc-common.c (option_optimization_table):
> 	Enable REE at -O2 and higher.
> 	* config/sparc/sparc.c (sparc_option_override): Disable it by default
> 	in 32-bit mode.
Very cool.  Ideally all targets would enable REE, but we're obviously 
not there yet.

With the fixes you've just done it's probably a lot more feasible to 
experiment with REE on other risc targets.

jeff