investigate PhaseChaitin::post_allocate_copy_removal after solaris removal

in postaloc.cpp:749
        // If the value occupies a register pair, record same info
        // in both registers.
        OptoReg::Name nreg_lo = OptoReg::add(nreg,-1);
        if( RegMask::can_represent(nreg_lo) && // Either a spill slot, or
            !lrgs(lidx).mask().Member(nreg_lo) ) { // Nearly always adjacent
          // Sparc occasionally has non-adjacent pairs.
          // Find the actual other value
          RegMask tmp = lrgs(lidx).mask();
          tmp.Remove(nreg);
          nreg_lo = tmp.find_first_elem();
        }
this piece of code need revisit if it is sparc only after solaris removal.