which option you opt to
If /DEBUG is specified, the default for /OPT is NOREF, and all functions are preserved in the image. To override this default and optimize a debugging build, specify /OPT:REF. Because /OPT:REF implies /OPT:ICF, we recommend that you also specify /OPT:NOICF to preserve identical functions in debugging builds. This makes it easier to read stack traces and set breakpoints in functions that would otherwise be folded together. The /OPT:REF option disables incremental linking.