Why can't I access a default argument in its initializer in gcc?

Question

This compiles in clang but not in gcc:

void f(int x = decltype(x){});

The error in gcc says that x was not declared in this scope but according to 3.3.2/1 the variable x should be in scope:

The point of declaration for a name is immediately after its complete declarator (Clause 8) and before its initializer (if any), except as noted below. [Example:

int x = 12;
{ int x = x; }

Here the second x is initialized with its own (indeterminate) value. — end example ]

So is clang correct? Should x be accessible in its own initializer?

PS: int x = x as a parameter fails in both compilers but I don't know why.

Answer 1

GCC is correct; that's not valid.

C++11 8.3.6/9 [dcl.fct.default] parameters of a function shall not be used in a default argument, even if they are not evaluated.