private static RegisterSpecList getRegs(Insn insn) {
    return getRegs(insn, insn.getResult());
  }
Gets the complete register list (result and sources) out of a given rop instruction. For insns
that are commutative, have two register sources, and have a source equal to the result, place
that source first.

@param insn {@code non-null;} instruction in question
@return {@code non-null;} the instruction's complete register list
android/android_framework/dex-maker/src/main/java/com/android/dx/dex/code/RopTranslator.java