GCC - Preserving statement expression results on stack

[Joe Perches <joe@xxxxxxxxxxx>]

I know that gcc preserves stack slots for statement expressions.

http://gcc.gnu.org/ml/gcc-patches/2002-02/msg00958.html

What about statement expressions that return arrays?
When does GCC free stack used by statement expression array returns?

For instance:

#define itoa(i) \
	({ char tmp[16]; sprintf(tmp, "%d", i); tmp; })

printf("%s %s\n", itoa(1), itoa(2));

is the printf output guaranteed to be "1 2" or is it undefined?