public void addPhiOperand(RegisterSpec registerSpec, SsaBasicBlock predBlock) {
    operands.add(new Operand(registerSpec, predBlock.getIndex(), predBlock.getRopLabel()));

    // Un-cache sources, in case someone has already called getSources().
    sources = null;
  }
Adds an operand to this phi instruction.

@param registerSpec register spec, including type and reg of operand
@param predBlock predecessor block to be associated with this operand
android/android_framework/dex-maker/src/main/java/com/android/dx/ssa/PhiInsn.java