docs: public int getInstanceSlot(Instruction ins, ConstantPoolGen cpg) throws DataflowAnalysisException {
          if (!isValid()) {
              throw new DataflowAnalysisException("Accessing invalid frame at " + ins);
          }
          int numConsumed = ins.consumeStack(cpg);
          if (numConsumed == Const.UNPREDICTABLE) {
              throw new DataflowAnalysisException("Unpredictable stack consumption in " + ins);
          }
          if (numConsumed > getStackDepth()) {
              throw new DataflowAnalysisException("Stack underflow " + ins);
          }
          return getNumSlots() - numConsumed;
      }