The DSP User Guides wrongly indicate that the pre-adder should be inside the DSP block in the following figures:
Figure 13. Pre-adder Square Mode (Intel FPGA Integer Arithmetic IP Cores User Guide)
Figure 36. Pre-adder Square Mode (Intel® Stratix® 10 Variable Precision DSP Blocks User Guide)
However, Intel® Stratix® 10 DSP atom does not support pre-adder square mode.
You can still use this feature by using the Intel FPGA Multiply Adder IP, but the pre-adder square mode is implemented as an external ALM.