[Bug c++/49974] missing -Wreturn-local-addr for indirectly returning reference to local/temporary

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=49974

--- Comment #18 from Martin Sebor <msebor at gcc dot gnu.org> ---
This detection is partially implemented in GCC 12 by the -Wdnagling-pointer:

$ cat pr49974.C && gcc -O -S -Wall pr49974.C

struct X { };

inline const X& f(const X& r) { return r; }

const X& g()
{
    X x;
    return f(x);  // !!!
}

const X& h()
{
    return f(X()); // !!!
}


struct Y {
    Y(int& i) : r(i) { }
    int& r;
};

Y f()
{
    int i=0;
    return Y(i);
}
pr49974.C: In function ‘const X& g()’:
pr49974.C:9:15: warning: using a dangling pointer to ‘x’ [-Wdangling-pointer=]
    9 |     return f(x);  // !!!
      |               ^
pr49974.C:8:7: note: ‘x’ declared here
    8 |     X x;
      |       ^
pr49974.C: In function ‘const X& h()’:
pr49974.C:14:17: warning: using a dangling pointer to an unnamed temporary
[-Wdangling-pointer=]
   14 |     return f(X()); // !!!
      |                 ^
pr49974.C:14:16: note: unnamed temporary defined here
   14 |     return f(X()); // !!!
      |                ^


For the test case in comment #17 GCC with -O1 issues:

pr49974-c17.C: In function ‘int main()’:
pr49974-c17.C:11:12: warning: using a dangling pointer to an unnamed temporary
[-Wdangling-pointer=]
   11 |   return x.i;
      |            ^
pr49974-c17.C:10:15: note: unnamed temporary defined here
   10 |   X&& x = f(X{});
      |               ^
pr49974-c17.C:11:12: warning: ‘<anonymous>.X::i’ is used uninitialized
[-Wuninitialized]
   11 |   return x.i;
      |            ^
pr49974-c17.C:10:15: note: ‘<anonymous>’ declared here
   10 |   X&& x = f(X{});
      |               ^