[Bug c/69104] New: invalid atomic memory order not diagnosed

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69104

            Bug ID: 69104
           Summary: invalid atomic memory order not diagnosed
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

Gcc silently accepts invocations of C11 atomic operations with an invalid
memory_order argument.  For example, it doesn't diagnose any of the invalid
calls in the test case below (and emits fences for most).

In contrast, Clang issues "warning: memory order argument to atomic operation
is invalid [-Watomic-memory-ordering]" for each of them and treats them as
no-ops.

$ cat z.c && /home/msebor/build/gcc-trunk-svn/gcc/xgcc
-B/home/msebor/build/gcc-trunk-svn/gcc -O2 -S -Wall -Wextra -Wpedantic
-o/dev/null z.c
#include <stdatomic.h>

/* atomic_store_explicit():
   The order argument shall not be memory_order_acquire,
   memory_order_consume, nor memory_order_acq_rel.  */

void store_consume (_Atomic int *i)
{
  atomic_store_explicit (i, 0, memory_order_consume);
}

void store_acquire (_Atomic int *i)
{
  atomic_store_explicit (i, 0, memory_order_acquire);
}

void store_acq_rel (_Atomic int *i)
{
  atomic_store_explicit (i, 0, memory_order_acq_rel);
}

/* atomic_load_explicit():
   The order argument shall not be memory_order_release nor
   memory_order_acq_rel.  */

int load_consume (_Atomic int *i)
{
  return atomic_load_explicit (i, memory_order_release);
}

int load_acq_rel (_Atomic int *i)
{
  return atomic_load_explicit (i, memory_order_acq_rel);
}