Initially reported at https://lore.kernel.org/r/YZdhYEVCgqh5MB3J@smile.fi.intel.com/.

Reproducer: https://godbolt.org/z/EcPP7o1T9

$ cat test.c
#define NULL ((void *)0)

struct foo {
        int x;
};

void bar(void) {
        struct foo *a;
        a->x = 1;
}

$ gcc --version
gcc (GCC) 11.1.0
Copyright (C) 2021 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ gcc -Wuninitialized -c -o /dev/null test.c
test.c: In function ‘bar’:
test.c:9:14: warning: ‘a’ is used uninitialized [-Wuninitialized]
    9 |         a->x = 1;
      |         ~~~~~^~~

$ clang --version
clang version 13.0.0
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/sbin

$ clang -fsyntax-only -Wuninitialized test.c
test.c:9:2: warning: variable 'a' is uninitialized when used here [-Wuninitialized]
        a->x = 1;
        ^
test.c:8:15: note: initialize the variable 'a' to silence this warning
        struct foo *a;
                     ^
                      = NULL
1 warning generated.

This seems like a poor suggestion, as it is going to just result in the user's program crashing (it probably already will but the hint does nothing to improve that). Perhaps it should be omitted if the pointer is dereferenced (or just altogether, since it is likely that a pointer is going to be dereferenced at some point in its lifetime)? Having the location of the variable is helpful in the warning but I think emitting the '= NULL' part of it is not helpful.