private static void setRegsUsed(BitSet regsUsed, RegisterSpec rs) {
    regsUsed.set(rs.getReg());
    if (rs.getCategory() > 1) {
      regsUsed.set(rs.getReg() + 1);
    }
  }
Sets the register as used in a bitset, taking into account its category/width.

@param regsUsed set, indexed by register number
@param rs register to mark as used
android/android_framework/dex-maker/src/main/java/com/android/dx/ssa/SsaBasicBlock.java