Use of atomic_int now fails with address argument to atomic operation must be a pointer to a trivially-copyable type

[Olivier Tilloy]

This appears to be a regression from clang 6.0.0 to 6.0.1 (also reported upstream: https://bugs.llvm.org/show_bug.cgi?id=37457).

The following code:

#include <stdatomic.h>
int main(int argc, char** argv) {
  atomic_int tmp = ATOMIC_VAR_INIT(-1);
  atomic_store_explicit(&tmp, 42, memory_order_relaxed);
  return 0;
}

fails to build:

$ clang-6.0 -std=gnu11 -Wall test.c
test.c:7:3: error: address argument to atomic operation must be a pointer to a trivially-copyable type ('_Atomic(int) *' invalid)
  atomic_store_explicit(&tmp, 42, memory_order_relaxed);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/bin/../lib/gcc/x86_64-linux-gnu/7.3.0/include/stdatomic.h:126:5: note: expanded from macro 'atomic_store_explicit'
    __atomic_store (__atomic_store_ptr, &__atomic_store_tmp, (MO)); \
    ^ ~~~~~~~~~~~~~~~~~~
1 error generated.

If I replace "atomic_int" by "int", the code builds and works as expected.

ProblemType: Bug
DistroRelease: Ubuntu 18.10
Package: clang-6.0 1:6.0.1-2ubuntu1
ProcVersionSignature: Ubuntu 4.15.0-23.25-generic 4.15.18
Uname: Linux 4.15.0-23-generic x86_64
ApportVersion: 2.20.10-0ubuntu3
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Mon Jul 9 10:33:31 2018
InstallationDate: Installed on 2018-07-06 (2 days ago)
InstallationMedia: Ubuntu 18.10 "Cosmic Cuttlefish" - Alpha amd64 (20180630)
SourcePackage: llvm-toolchain-6.0
UpgradeStatus: No upgrade log present (probably fresh install)

[Olivier Tilloy (osomon)]

In /usr/lib/gcc/x86_64-linux-gnu/7.3.0/include/stdatomic.h, before the definition of the atomic_store_explicit macro:

   Note that these macros require __typeof__ and __auto_type to remove
   _Atomic qualifiers (and const qualifiers, if those are valid on
   macro operands).

It looks like the regression might be that __auto_type doesn't remove the _Atomic qualifier any longer?

[Olivier Tilloy (osomon)]

Debian bug report: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=903709

This was fixed with version 1:6.0.1-4.