I bet it just ignores the attribute that is not how the attribute is supposed to work.
We output error in this case intentionally (and warning in at the same spot if function is declared inline and -Winline is given). Functions marked always_inlined really ought to be always inlined and attribute is supposed to be useable in the cases where compilation would fail otherwise (such as SSE buitins). Our documentation is however not particularly clear here, perhaps it should be updated... Honza
