Demonstrate valgrind false positive for "Conditional jump or move depends on uninitialised value(s)"

test_valgrind_cmpxchg.c

#include <stdlib.h>
#include <stdio.h>
#include <stdbool.h>

static int foo = 42;
    
#define _arch_load(addr, memorder)                                      \
    ({                                                                  \
        __auto_type _addr = addr;                                       \
        typeof(*_addr) _store;                                          \
        __atomic_compare_exchange(&_store, &_store,                     \
                                  _addr, false, memorder, memorder);    \
        _store;                                                         \
    })

int main(int argc, char** argv) {
    int f = _arch_load(&foo, __ATOMIC_SEQ_CST);
    printf("f = %d\n", f);
    return EXIT_SUCCESS;
}

// gcc test_valgrind_cmpxchg.c -o test_valgrind_cmpxchg
// valgrind ./test_valgrind_cmpxchg

// $ valgrind --version
// valgrind-3.19.0