Hello

This patch fixes a bug introduced in a previous patch adding support for 
generating native instructions for the exp2 and log2 patterns. The 
problem is that the name of the instruction implementing the exp2 
operation is v_exp (and not v_exp2), and similarly log2 is implemented 
by v_log, so we cannot use the RTL name of the operation when outputting 
the instruction.

I've added an extra iterator for the GCN operation name and used that 
when outputting instructions instead. I have also added an extra 
testcase for GCN that exercises this case.

Okay for trunk?

Thanks

Kwok