`-Watomic-alignment` too eager?

[glandium]

Bugzilla Link	38593
Version	unspecified
OS	Linux
CC	@DimitryAndric,@froydnj

Extended Description

$ cat <<EOF > test.c

#include <stdint.h>

uint64_t
loadSeqCst(uint64_t* addr) {
  uint64_t v;
  __atomic_load(addr, &v, __ATOMIC_SEQ_CST);
  return v;
}

EOF
$ clang-7 -o test.o -c test.c -m32
test.c:6:3: warning: misaligned or large atomic operation may incur significant performance penalty [-Watomic-alignment]
  __atomic_load(addr, &v, __ATOMIC_SEQ_CST);
  ^
1 warning generated.

This seems too eager for a warning that is emitted without even passing a -Wsomething on the command line.

[DimitryAndric]

Yes, every time an atomic function is translated into a libcall, you get this warning. We've disabled this warning in FreeBSD too, at least for specific architectures such as arm before armv6:

freebsd/freebsd-src@23015fe