pthread_spin_unlock on IA64

["Boehm, Hans" <hans dot boehm at hp dot com>]

I've spent some time looking into the slightly esoteric question of what
fences actually need to be included in pthread locking operations.  As
part of that I looked a bit at what nptl actually does.

I ran into one case in which the result seems clearly nonsensical,
independent of the more subtle issues.  On IA64, at least as of
glibc-2.3.6 on my Debian machine, pthread_mutex_unlock() generates
basically

mf
st.rel4 ...

I cannot see any conceivable reason for the mf, other than to slow down
the code.

I'm also not entirely sure what source file this corresponds to.  Is
./nptl/sysdeps/pthread/pthread_spin_unlock.c somehow being used instead
of ./nptl/sysdeps/ia64/pthread_spin_unlock.c?  Then the result would
make sense.

(I did not verify this with 2.4.  But the code does not appear to have
changed.  I also first noticed some time ago, so it seems to be fairly
stable across glibc versions.)

[Please copy me in reply.]

Thanks.

Hans