[Bug driver/63660] New: [4.8-4.9+] -Wmaybe-uninitialized false positive with -O1 and more

[ed0.88.prez at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63660

            Bug ID: 63660
           Summary: [4.8-4.9+] -Wmaybe-uninitialized false positive with
                    -O1 and more
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: driver
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ed0.88.prez at gmail dot com

Here, this code:

cat bug.i
typedef struct
{
 int a;
 int b;
 int c;
 int d;
 int e;
 int f;
 int g;
 int h;
 int i;
 int j;
} X;

X *XX(int);

int G();

static void F()
{
 X *x;
 int m, n;
 int xa, xb, xc, xd, xe, xf, xg, xh, xi, xj;

 m = G();
 n = G();
 if ( n & 1 ) xa = G();
 if ( n & 2 ) xb = G();
 if ( n & 4 ) xc = G();
 if ( n & 32 ) xd = G();
 if ( n & 16 ) xe = G();
 if ( n & 64 ) xf = G();
 if ( n & 256 ) xg = G();
 if ( n & 512 ) xh = G();
 if ( n & 1024 ) xi = G();
 if ( n & 2048 ) xj = G();

 if ( m >= 64 ) return;
 x = XX(m);
 if ( n & 1 ) x->a = xa;
 if ( n & 2 ) x->b = xb;
 if ( n & 4 ) x->c = xc;
 if ( n & 32 ) x->d = xd;
 if ( n & 16 ) x->e = xe;
 if ( n & 64 ) x->f = xf;
 if ( n & 256 ) x->g = xg;
 if ( n & 512 ) x->h = xh;
 if ( n & 1024 ) x->i = xi;
 if ( n & 2048 ) x->j = xj;
}

void H()
{
 F();
}
EOF

Compiled with -O1 -Wmaybe-uninitialized (implied by -Wall), reports this
message:

bug.i: In function ‘H’:
bug.i:49:23: warning: ‘xj’ may be used uninitialized in this function
[-Wmaybe-uninitialized]
  if ( n & 2048 ) x->j = xj;
                       ^
bug.i:23:42: note: ‘xj’ was declared here
  int xa, xb, xc, xd, xe, xf, xg, xh, xi, xj;
                                          ^
This code is a very reduced testcase from a large program.