public List<SsaBasicBlock> predBlocksForReg(int reg, SsaMethod ssaMeth) {
    ArrayList<SsaBasicBlock> ret = new ArrayList<SsaBasicBlock>();

    for (Operand o : operands) {
      if (o.regSpec.getReg() == reg) {
        ret.add(ssaMeth.getBlocks().get(o.blockIndex));
      }
    }

    return ret;
  }
Returns the list of predecessor blocks associated with all operands that have {@code reg} as an
operand register.

@param reg register to look up
@param ssaMeth method we're operating on
@return list of predecessor blocks, empty if none
android/android_framework/dex-maker/src/main/java/com/android/dx/ssa/PhiInsn.java