destroying pointed-to object explicitly with decltype

I have:

T* p;

and I'd like to do:

p->~decltype(*p)();

However, it doesnt work.

p->~T();

does work, but it like to do it with decltype(), if possible.

Error message:

error: expected class-name before 'decltype'

EDIT: use case

I'm trying to avoid the use of VLA for an array allocated on the stack using alloca + placement new of the array. After the placement new, the objects in the stack array need to be explicitly destroyed. I know how to solve the problem, I can do:

using T = ::std::remove_reference_t<decltype(*p)>;
p->~T();

But, I'm puzzled why this is necessary.