they prefer the destination register to be last. Thus, two new classes were made
for them that accomodate for having this layout of operands (F3_1rd, F3_2rd).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@6564 91177308-0d34-0410-b5e6-96231b3b80d8