[Bug c++/66192] New: C++ static initializer unnecessary __cxa_guard_acquire for TARGET_RELAXED_ORDERING

["dje at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66192

            Bug ID: 66192
           Summary: C++ static initializer unnecessary __cxa_guard_acquire
                    for TARGET_RELAXED_ORDERING
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dje at gcc dot gnu.org
  Target Milestone: ---

// static_init.cc

int* f(void) {
  static int* p = new int;
  return p;
}

$ g++ -O2 -S -fno-exceptions static_init.cc

generates an unnecessary call to __cxa_guard_acquire on what should be the fast
path for targets with TARGET_RELAXED_ORDERING defined.  The guard should be an
atomic variable accessed with the equivalent of __atomic_load(ACQUIRE) instead
of a heavy-weight __cxa_guard_acquire() call invoking heavier-weight
synchronization.