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From: "msebor at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/60488] New: missing -Wmaybe-uninitialized on a conditional with goto
Date: Mon, 10 Mar 2014 16:17:00 -0000
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X-Bugzilla-Component: c
X-Bugzilla-Version: 4.8.2
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60488

            Bug ID: 60488
           Summary: missing -Wmaybe-uninitialized on a conditional with
                    goto
           Product: gcc
           Version: 4.8.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gmail dot com

The -Wmaybe-uninitialized option is documented like so: "For an automatic
variable, if there exists a path from the function entry to a use of the
variable that is initialized, but there exist some other paths for which the
variable is not initialized, the compiler emits a warning if it cannot prove
the uninitialized paths are not executed at run time."

In the program below, when f(&a) returns zero, the variable b is considered to
have been initialized by the call to f(&b) when it's used as the argument in
the first call to g(b). However, when f(&a) returns non-zero, the variable b is
used uninitialized in the second call to g(b). Therefore, there exists a path
through the function where b is used initialized as well as one where it's used
uninitialized. Thus, GCC should issue a warning. It, however, does not.

$ cat t.c && gcc -O2 -Wuninitialized -Wmaybe-uninitialized -c -o/dev/null t.c
int f (int**);
void g (int*);

int foo (void) {
    int *a, *b;

    if (f (&a) || f (&b))
        goto end;

    g (a);
    g (b);
    return 0;
end:
    g (b);
    return 1;
}