unused parameter elimination optimization

Question

Is there an "unused function parameter elimination optimization", when I use enabler as following:

template< typename T >
void f(T x, typename std::enable_if< some_predicate< T > >::type * = nullptr) { /* do something useful with x */; }

?

I mean, will generate extra code for void * parameter passing (for example, for GCC 4.8 compiler)?

And what about in light of lto/ltcg presence?

Answer 1

Strictly, doing this violates the ABI, as far as I am aware- ie, some other compiler that did not optimize might pass in a value there.

However, in my experience, Clang has an immensely irritating habit of removing parameters it views as redundant- especially values of empty types. So I would suggest that the compiler might do if it can prove the value is unused.