Consider the following sample code:

struct A
{
        static const unsigned alignment = 32;
        
        char data[1234] __attribute__((aligned(alignment /*+ 0*/)));
} __attribute__((aligned(A::alignment /* + 0 */)));

g++ (r193606) complains that "requested alignment is not an integer constant", but when the "+ 0" part is uncommented, the requested alignment magically becomes a constant.