Following emits a warning about potential use of uninitialized variable,
even though the variable initialization and it's use are guarded by the
same predicate.

int f (void);

int g (int a)
{
    int b;

    if (a) b = f ();
    asm volatile ("#");
    if (a) return b;
    return 1;
}

$ gcc -O -Wuninitialized -c repro.c                
repro.c: In function 'g':
repro.c:5: warning: 'b' may be used uninitialized in this function

This happens with gcc 4.3.0 and 4.3.1