It is necessary to add this flag for compilation on Windows

[bburrough]

filtered_lrelu.cpp uses "if constexpr" which is c++17, and will otherwise fail with the following error.

filtered_lrelu.cpp(147): error C4984: 'if constexpr' is a C++17 language extension

Please note, I have not tested this on other platforms (e.g. Ubuntu), where this flag might be inappropriate.

[bburrough]

If you don't wish to adopt this flag, you might alternatively consider removing "if constexpr" for greater portability.

[PDillis]

I just tested this on Ubuntu 20.04 and it works, so the flag could be added in general to benefit Windows users.

[PDillis]

Actually, I just tested it again with another code (random interpolation in particular), and it fails. I recommend adding a os check as follows:

def _init():
    global _plugin
    # Bob Burrough's PR (#45) so that the plugins work in Windows: https://github.com/NVlabs/stylegan3/pull/45
    extras = {}
    if os.name == 'nt':
        extras['extra_cflags'] = ['/std:c++17']
    if _plugin is None:
        _plugin = custom_ops.get_plugin(
            module_name='filtered_lrelu_plugin',
            sources=['filtered_lrelu.cpp', 'filtered_lrelu_wr.cu', 'filtered_lrelu_rd.cu', 'filtered_lrelu_ns.cu'],
            headers=['filtered_lrelu.h', 'filtered_lrelu.cu'],
            source_dir=os.path.dirname(__file__),
            extra_cuda_cflags=['--use_fast_math'],
            **extras,
        )
    return True