llvmはそういう情報を持っている様です。 https://github.com/apple/swift-llvm/blob/stable/include/llvm/Analysis/ConstantFolding.h#L140-L142
/// canConstantFoldCallTo - Return true if its even possible to fold a call to /// the specified function. bool canConstantFoldCallTo(ImmutableCallSite CS, const Function *F);