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Bug#884431: gcc-7: miscompile pthread_barrier.c from glibc with -mcpu=ultrasparc

Package: gcc-7
Version: 7.2.0-17
Severity: normal

When pthread_barrier.c from glibc is compiled with gcc-7 and
-mcpu=ultrasparc (as opposed to the default -mcpu=v9), the futex
code is miscompiled. This causes the rt/tst-mqueue5, nptl/tst-signal6
and nptl/tst-tls2 to fail with:

  The futex facility returned an unexpected error code.

I haven't been able to reproduce the issue with GCC 6. That said it
looks like the issue is quite dependent of the instruction scheduling
as slightly changing the code around for debugging purpose makes the
problem to vanish.

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