unresolved external symbol referenced in function removed by /OPT:REF

Question

I have a function bar() that I don't actually call, that calls unimplemented foo():

void foo();
void bar()
{
    foo();
}
int main()
{

}

If I package each function in a separate section/COMDAT and ask the linker to remove unused sections/COMDAT, I can get gcc to compile the program

gcc -ffunction-sections -Xlinker --gc-sections LinkerFunctions.cpp

but the equivalent in Visual C++ 2019

cl /Gy LinkerFunctions.cpp /link /OPT:REF

barks that

error LNK2019: unresolved external symbol "void __cdecl foo(void)" (?foo@@YAXXZ) referenced in function "void __cdecl bar(void)" (?bar@@YAXXZ)

How can I get msvc to compile the program?

@DanielA.White Visual Studio 2019. Just updated the question. Thanks. — Bruno Martinez, Apr 20 '20 at 19:41
Might be the same issue: [\[SO\]: Why are dependencies different between these two MSVC C++ project configurations (@CristiFati's answer)](https://stackoverflow.com/a/75785719/4788546). — CristiFati, Mar 20 '23 at 00:14

score 5 · Answer 1 · answered Apr 20 '20 at 19:49

5

Got your example working by adding inline, even after adding __declspec(noinline) to prevent actual inlining.

void foo();

__declspec(noinline)
inline void bar()
{
    foo();
}

int main()
{

}

Tried because the documentation says:

Inlined functions and member functions defined inside a class declaration are always COMDATs.

Not sure however if it is robust solution, or works just in this particular case.

answered Apr 20 '20 at 19:49

Alex Guteniev

`static void bar() { ... }` appears to work, too. It looks like otherwise VS has a problem realizing that `bar` is not referenced from elsewhere, even with "*whole program optimizations*" turned on. – dxiv Apr 27 '20 at 00:48

score 2 · Answer 2 · answered May 02 '20 at 17:05

2

Accidentally found a linker switch for that:

cl incomplete.cpp /link /FORCE:UNRESOLVED

Will give a warning but in fact will work.

answered May 02 '20 at 17:05

Alex Guteniev

2 Answers2