Although I demonstrated this using 4.1.2 on my host, it probably affects
other versions as well.

As the following code shows:

    gcc -c -O1 -Wall -Werror uninitialized-warning.c

    extern void called_function(unsigned p);
    extern unsigned g;

    void
    f0(unsigned parm)
    {
       unsigned v;
       if (parm == 0) {
          v = 4;
       }
       called_function(v);
    }

    void
    f1(unsigned parm)
    {
       unsigned v;
       if (parm == 0) {
          v = 4;
       } else {
          g = 0;
       }
       called_function(v);
    }

    void
    f2(unsigned parm)
    {
       unsigned v;
       called_function(v);
    }

gcc does not produce the 'uninitialized' warning when the automatic
variable is conditionally assigned.

This gives a very bad false sense of security that the automatic
variables are indeed initialized.