Documentation on {} and | in inline asm to allow Intel syntax?

[Danny Smith]

Hi,

I can't find  documentation on the use of {} and | in inline asm
(as in this from libstdc++-v3/config/cpu/i486/atomicity.h) 

 __asm__ __volatile__ ("lock; xadd{l} {%0,%1|%1,%0}"
        ....)
to allow Intel syntax in addition to default AT&T

Specifically, can anyone tell me when this feature was introduced?

Thanks,

Danny