Re: [PATCH] libstdc++: Remove some more unconditional uses of atomics

[Christophe Lyon <christophe.lyon@linaro.org>]

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On Thu, 14 Sept 2023 at 11:06, Jonathan Wakely <jwakely@redhat.com> wrote:

> On Thu, 14 Sept 2023 at 09:41, Christophe Lyon
> <christophe.lyon@linaro.org> wrote:
> >
> >
> >
> > On Thu, 14 Sept 2023 at 10:17, Jonathan Wakely <jwakely@redhat.com>
> wrote:
> >>
> >> On Thu, 14 Sept 2023 at 08:44, Christophe Lyon
> >> <christophe.lyon@linaro.org> wrote:
> >> >
> >> > Hi,
> >> >
> >> >
> >> > On Wed, 13 Sept 2023 at 14:32, Jonathan Wakely <jwakely@redhat.com>
> wrote:
> >> >>
> >> >> Tested x86_64-linux and aarch64-linux. I intend to push this to
> trunk.
> >> >>
> >> >> -- >8 --
> >> >>
> >> >> These atomics cause linker errors on arm4t where __sync_synchronize
> is
> >> >> not defined. For single-threaded targets we don't need the atomics.
> >> >>
> >> >
> >> > I ran the tests on arm-eabi default config (so, armv4t) with this
> patch, and here is the list of remaining UNRESOLVED tests:
> >> >  29_atomics/atomic/compare_exchange_padding.cc
> >> > 29_atomics/atomic/cons/value_init.cc
> >> > 29_atomics/atomic_float/value_init.cc
> >> > 29_atomics/atomic_integral/cons/value_init.cc
> >> > 29_atomics/atomic_ref/compare_exchange_padding.cc
> >> > 29_atomics/atomic_ref/generic.cc
> >> > 29_atomics/atomic_ref/integral.cc
> >> > 29_atomics/atomic_ref/pointer.cc
> >> > experimental/polymorphic_allocator/construct_pair.cc
> >> >
> >> > all of them are due to undefined reference to __sync_synchronize
> >> > (some also reference __atomic_compare_exchange_4, etc...)
> >> >
> >> >
> >> > IIUC, this should not be the case for
> experimental/polymorphic_allocator/construct_pair.cc ?
> >> > The reference for __sync_synchronize is near the beginning of
> test0[123]
> >> > from a call to __atomic_load_n line 835 of atomic_base.h
> >> > not sure where it comes from, the .loc directive indicates line 28 of
> the testcase which is the opening brace
> >>
> >> Doh, I removed the atomics from <memory_resource> but this is
> >> <experimental/memory_resource>, which has a separate implementation.
> >>
> >> I'll make a change to <experimental/memory_resource> as well, thanks
> >> for catching my silly mistake.
> >>
> >
> > You're welcome.
> > So I'll shrink my patch and add dg-require-thread-fence only to the few
> 29_atomics tests listed above.
>
> Great, thanks. That's approved for trunk then.
>
> N.B. if you'd prefer to add { dg-require-effective-target thread_fence
> } instead of { dg-require-thread-fence "" } then that's fine, just
> note that the effective target uses an underscore not a hyphen. The
> dg-require-thread-fence proc just uses the proc that checks the
> thread_fence effective target, so both forms do the same thing.
>
> Ha! Just sent v2, I kept  dg-require-thread-fence, because it was used
elsewhere in the libstsdc++ testsuite.

Thanks,

Christophe