Incorrect const qualifier?

[DavidCallahan]

Using a near-trunk build of clang which as a new semantic check, I get this error:

include/boost/atomic/detail/ops_gcc_x86_dcas.hpp:408:16: error: address argume\nt to atomic builtin cannot be const-qualified ('const volatile boost::atomics::detail::gcc_dcas_x86_64::storage_type *' (aka 'constvolatile unsigned __int128 *') invalid)
        return __sync_val_compare_and_swap(&storage, value, value);
               ^                           ~~~~~~~~
1 error generated.

which is generated due to the "const" declaration in this static function:
https://github.com/boostorg/atomic/blob/develop/include/boost/atomic/detail/ops_gcc_x86_dcas.hpp#L402

The error seems correct but so does the code. I worked around this by casting away the const operand to the intrinsic.

        return __sync_val_compare_and_swap(
            const_cast<storage_type volatile*>(&storage), value, value);

[Lastique]

I can't reproduce this. What clang version do you use?

[Lastique]

On 07/18/18 00:30, David Callahan wrote: Using current trunk (master). Here is a test case |#define BOOST_ATOMIC_DETAIL_X86_HAS_CMPXCHG16B 1 #include <boost/atomic.hpp> typedef boost::atomics::detail::gcc_dcas_x86_64<true> DCAS; const volatile DCAS::storage_type data = 0; unsigned get() { return DCAS::load(data, boost::memory_order::relaxed); } |

The current develop doesn't fail the compilation with clang 6.0, but the test case is not valid. boost::atomic objects (and their internal storage) must reside in writable memory. load() may issue store operation on the storage memory even though the stored value doesn't change.

[fiesh]

With boost 1.67 and clang-7, I can reproduce the issue with this:

echo '#include <boost/log/utility/setup.hpp>' > /tmp/a.cpp && clang++ -c -march=haswell /tmp/a.cpp

In file included from /tmp/a.cpp:1:
In file included from /usr/include/boost/log/utility/setup.hpp:20:
In file included from /usr/include/boost/log/utility/setup/common_attributes.hpp:22:
In file included from /usr/include/boost/log/attributes/counter.hpp:26:
In file included from /usr/include/boost/atomic/atomic.hpp:20:
In file included from /usr/include/boost/atomic/fences.hpp:21:
In file included from /usr/include/boost/atomic/detail/operations.hpp:17:
In file included from /usr/include/boost/atomic/detail/operations_lockfree.hpp:21:
In file included from /usr/include/boost/atomic/detail/ops_gcc_atomic.hpp:24:
/usr/include/boost/atomic/detail/ops_gcc_x86_dcas.hpp:408:16: error: address argument to atomic builtin cannot be const-qualified ('const volatile boost::atomics::detail::gcc_dcas_x86_64::storage_type *'
      (aka 'const volatile unsigned __int128 *') invalid)
        return __sync_val_compare_and_swap(&storage, value, value);
               ^                           ~~~~~~~~
1 error generated.

[fiesh]

6e14ca2 indeed fixes the issue -- boost 1.69 works! Thanks!

[Lastique]

On 12/18/18 3:18 PM, fiesh wrote: @Lastique Any chance this can be re-opened?

No, the problem has been fixed already.

[fiesh]

On 12/18/18 3:18 PM, fiesh wrote: @Lastique Any chance this can be re-opened?
No, the problem has been fixed already.

Yeah that's why I had removed the comment before your answer and replaced it with the other one.

[timgivois]

So basically, this is fixed in 1.69 which is incompatible with MacOS and that means you won't fix 1.67....

[bilalebi]

I had the same issue but upgrading to boost 1.72 solved it.

I'm on Mac Catalina