User guide

25-25
Source Protection
The -Xnomangle option should only be used on top level modules,
i.e., ones that are not called by any other module in the design being
mangled. The code which performs the mangling knows how to
identify module and port declarations, but not module references.
Thus, if you exempt a module which is referenced by some other
module, the reference will try to use the mangled name instead of the
original (and fail).