[Bug libgomp/38270] New: libgomp test failures due to missing memory barrier

["janis at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

Libgomp test libgomp.c/atomic-3.c started failing with wrong answers on power5
and power6 systems for -m32, and tests nqueens-1.c and sort-1.c started hanging
intermittently for both -m32 and -m64 on those systems, with the addition of
r139969, which removes the memory barrier from rs6000_split_lock_test_and_set. 
Adding back the memory barrier allows those tests to pass again.

David Edelsohn told me that sync_lock_test_and_set does not require the
stricter semantics of a memory barrier and if libgomp needs the memory barrier
then it must emit one itself.

The patch submission for r139969,
http://gcc.gnu.org/ml/gcc/2008-09/msg00038.html, has followups from David and
from Richard Henderson briefly discussing the semantics of
sync_lock_test_and_set.


-- 
           Summary: libgomp test failures due to missing memory barrier
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libgomp
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: janis at gcc dot gnu dot org
GCC target triplet: powerpc64-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38270