Function LLVMGetOrInsertFunction 

pub unsafe extern "C" fn LLVMGetOrInsertFunction(
    M: LLVMModuleRef,
    Name: *const c_char,
    NameLen: size_t,
    FunctionTy: LLVMTypeRef,
) -> LLVMValueRef

Obtain or insert a function into a module.

If a function with the specified name already exists in the module, it is returned. Otherwise, a new function is created in the module with the specified name and type and is returned.

The returned value corresponds to a llvm::Function instance.

See llvm::Module::getOrInsertFunction().