It’s not clear how many people enjoy looking at programs that make compilers crash — but this post is for them (and me). Our paper on producing reduced test cases for compiler bugs contained a large table of results for crash bugs. Below are all of C-Reduce’s reduced programs for those bugs.

Can we conclude anything just by looking at these? It’s hard to say… many of these C fragments are not obviously hard to compile — to see the problem we would need to know the details of the translation to a particular compiler’s intermediate representation.

In general, we don’t know of any way to make these programs much smaller. In other words, C-Reduce already implements most of the tricks we can think of. It will always be the case that an experienced compiler developer who understand a particular bug will be able to produce considerably better reduced test cases than C-Reduce can. Our goal, rather, is to create tests that a naive user cannot improve very much. So if you see interesting opportunities to improve these test cases, we’d love to hear about it. The current version of C-Reduce fails to implement optimizations such as constant folding, constant propagation, and loop peeling. We haven’t seen much need for these, though.

These are the verbatim tool output; there are definitely some formatting warts.

C1 : Crashes Clang 2.6 at -O0:

#pragma pack(1)
struct S1 {
  int f0;
  char f2
};
struct {
  struct S1 f0
    }
a[] = { 0 }
      ;

C2 : Crashes Clang 2.6 at -O2:

struct S0 {
  int f0:1;
  int f4
}
a;
void
fn1 () {
  struct S0 b[][1][1] = { 0 };
  b[0][0][0] = a;
}

C3 : Crashes Clang 2.6 at -O2:

unsigned short a;
int b;
char c;
short
fn1 () {
  return 1 / a;
}
void
fn2 () {
  b = fn1 ();
  char d = b;
  c = d % 3;
}

C4 : Crashes Clang 2.6 at -O3:

int a, b, c, d, e;
#pragma pack(1)
struct S0 {
  int f0:14;
  int f1:13;
  int f2:28;
  int f3:23;
  int f4:12
};
void fn1 (struct S0);
void
fn2 () {
  int f;
lbl_2311:
  ;
  struct S0 g = { 0, 0, 1 };
  fn1 (g);
  b && e;
  for (; c;) {
    if (d)
      goto lbl_2311;
    f = a && 1 ? 0 : 1;
    g.f4 = f;
  }
}

C5 : Crashes Clang 2.6 at -O2:

 int crc32_context, g_2 = 0, g_5;
int g_8;
int *g_39, *g_371;
int g_81;
int func_1_l_15 ;
static short safe_add_func_int16_t_s_s ( short si1, int si2 ) {
    return si1 > 67 ? si1 : si1 + si2;
  }
   
   
   
   
    
   
    static int func_1 (  ) {
    int l_462 = 0;
    g_2 = 0;
    for ( ;
  g_2 < 12;
  g_2 = safe_add_func_int16_t_s_s ( g_2, 5 ) )     {
       g_5 = 1;
       for ( ;
 g_5;
 ++g_5 ) 	{
 	  g_8 = 1;
 	  for ( ;
 g_8 >= 0;
 g_8 = g_8 - 1 ) 	    {
 	      func_1_l_15 = 1;
  	      for ( ;
 func_1_l_15;
 		    func_1_l_15 =   func_1_l_15  - 1  ) 		if ( g_8 ) 		  break;
 	    }
 	  g_371 = &l_462;
 	  int *l_128 = &g_81;
 	  *l_128 = *g_39;
 	}
 *g_371 =    0 != 0   ;
     }
    return 0;
  }
   int main (  ) {
    func_1 (  );
    crc32_context = g_2;
    crc32_context += g_5;
  }
  

C6 : Crashes Clang 2.6 at -O0:

#pragma pack(1)
struct S2 {
  int f1;
  short f4
};
struct S3 {
  struct S2 f1;
  int f3:14
};
struct {
  struct S3 f3
    }
a = { 0, 0, 0 };

C7 : Crashes Clang 2.6 at -O1:

int *a;
static int **b;
int c, d, e;
void
fn1 () {
  d = &b == c;
  for (;;) {
    int **f = &a;
    if (e) {
    } else
      b = f;
    if (**b)
      continue;
    **f;
  }
}

C8 : Crashes Clang 2.6 at -O1:

#pragma pack(1)
struct S0 {
  int f3;
  char f4
};
struct {
  struct S0 f6;
  int f8
}
a = { 0, 0, 0 };

C9 : Crashes Clang 2.6 at -O2:

struct S0 {
  int f0;
  int f1;
  short f3;
  int f7;
  int f8
}
b;
int a, c, d, e, f;
void
fn1 (struct S0 p1) {
  d++;
  c = p1.f8;
  e = 0;
  a = p1.f7;
}
void
fn2 () {
  e = 0;
  for (; e; e++) {
    if (d)
      for (;;) {
      }
    --f;
  }
  fn1 (b);
}

C10 : Crashes Clang 2.6 at -O1:

union U2 {
  int f0;
  unsigned short f2
}
b;
static int a = 1;
void
fn1 (int p1, unsigned short p2) {
}
int fn2 (union U2);
union U2 fn3 ();
static unsigned long long
fn5 () {
  fn1 (b.f2, b.f0);
  return 0;
}
static char
fn4 () {
  fn5 ();
  return 0;
}
int
main () {
  a || fn2 (fn3 (fn4 () ) );
}

C11 : Crashes Clang 2.7 at -O1:

int *a;
static int **b;
int c, d, e;
void
fn1 () {
  d = &b == c;
  for (;;) {
    int **f = &a;
    if (e) {
    } else
      b = f;
    if (**b)
      continue;
    **f;
  }
}

C12 : Crashes Clang 2.7 at -O0:

char a;
unsigned char b;
int c;
void
fn1 () {
  (b ^= c) != a;
}

C13 : Crashes Clang 2.7 at -O2:

int a, b;
void fn1 ();
void
fn2 (short p1) {
  short c;
  c = (65532 | 3) + p1;
  fn1 (c && 1);
  b = (0 == p1) * a;
}

C14 : Crashes GCC 3.2.0 at -O1:

void
fn1 () {
  struct S0 *a;
  struct S0 *b, *c = &a;
  struct S0 **d = &c;
  if (&b == &a) {
  }
}

C15 : Crashes GCC 3.2.0 at -O3:

volatile int a, b, c, i;
char d;
void
fn1 () {
  int e;
  {
    for (;; c++) {
      int f[50] = { };
      if (b) {
        {
          0;
          {
            {
              int g = a, h = d;
              e = h ? g : g / 0;
            }
          }
          a = e;
        }
      }
    }
  }
}
void
main () {
  i = 0 / 0;
  a;
}

C16 : Crashes GCC 3.2.0 at -O3:

int a, c;
volatile int b;
void
fn1 () {
  b;
  for (;;)
    break;
  int d = b, e = a;
  c = a ? d : d % 0;
}
void
fn2 () {
  if (0 % 0)
    b;
}

C17 : Crashes GCC 3.2.0 at -O2:

union U1 {
  int f0;
  char f1
};
void
fn1 (union U1 p1) {
  p1.f1 = 0;
  for (; p1.f1;) {
  }
}

C18 : Crashes GCC 3.2.0 at -O1:

int a, b;
void
fn1 () {
  b = 4294967290UL <= a | b;
}

C19 : Crashes GCC 3.2.0 at -O3:

int a, b, c;
int
fn1 (int p1, int p2) {
  return p1 - p2;
}
void
fn2 () {
  int d;
  int **e;
  int ***f = &e;
  d = a && b ? a : a % 0;
  if (fn1 (f == 0, 2) )
    c = ***f;
}

C20 : Crashes GCC 3.3.0 at -O3:

int a, b, d;
struct S0 {
  int f3
};
int *volatile c;
void fn1 (struct S0);
void
fn2 () {
  int e;
  struct S0 **f;
  struct S0 ***g = &f;
  (a && b && b ? 0 : b) > (&c && 0);
  e = 0 == g;
  d = e >> 1;
  for (;;)
    fn1 (***g);
}

C21 : Crashes GCC 3.4.0 at -O3:

int a, b;
struct U0 {
  char f0;
  int f2
};
void
fn1 () {
  struct U0 c;
  for (; c.f0 != 1; c.f0 = c.f0 + a)
    b -= 1;
}

C22 : Crashes GCC 3.4.0 at -O3:

int a, b, d, e;
struct S0 {
  int f3
};
int *c;
void fn1 (struct S0);
void
fn2 () {
  struct S0 **f;
  struct S0 ***g = &f;
  (a && b && b ? 0 : b) > (&c == d);
  e = 1 < (0 == g);
  for (;;)
    fn1 (***g);
}

C23 : Crashes GCC 4.0.0 at -O2:

int ***a;
int b;
int *c;
void
main () {
  if (&c == a)
    b = 0 == *a;
}

C24 : Crashes GCC 4.0.0 at -O2:

int a[][0];
int *const b = &a[0][1];
int
fn1 () {
  return *b;
}

C25 : Crashes GCC 4.0.0 at -O0:

int a, b;
unsigned char c;
void
fn1 () {
  (0 >= a & (0 || b) ) > c;
}

C26 : Crashes GCC 4.0.0 at -O1:

struct {
  int f9:1
}
a;
const int b[] = { 0 };
void fn1 ();
void
main () {
  for (;;) {
    a.f9 = b[0];
    fn1 ();
  }
}

C27 : Crashes GCC 4.0.0 at -O0:

int a, c;
unsigned char b;
void
fn1 () {
  b > (c > 0 & 0 < a);
}

C28 : Crashes GCC 4.0.0 at -O2:

int **a[][0];
static int ***const b = &a[0][1];
void fn1 ();
int
fn2 () {
  return ***b;
  fn1 ();
}
void
fn1 () {
  **b;
}

C29 : Crashes GCC 4.1.0 at -O1:

volatile int ***a;
int b;
int **c;
void
fn1 () {
  if (&c == a)
    b = 0 == *a;
}

C30 : Crashes GCC 4.1.0 at -O1:

struct {
  int f0;
  int f2
}
a;
int b;
void
fn1 () {
  a.f2 = 0;
  int *c[] = { 0, 0, 0, 0, &a.f0, 0, 0, 0, &a.f0 };
  b = *c[4];
}

C31 : Crashes GCC 4.1.0 at -O2:

int a, b;
unsigned c;
void
fn1 () {
  for (; c <= 0;)
    if (b < c)
      a = 1 && c;
}

C32 : Crashes GCC 4.1.0 at -O1:

unsigned a;
int b;
void
main () {
  unsigned c = 4294967295;
  int d = c;
  b = a <= d || a;
}

C33 : Crashes GCC 4.1.0 at -O1:

const volatile long a;
void
main () {
  printf ("%d\n", (int) a);
}

C34 : Crashes GCC 4.1.0 at -O3:

int a, b;
union U1 {
  int f0;
  int f1
};
void
fn1 () {
  union U1 c = { 1 };
  int d = 1;
  if ( (c.f1 & a ? c.f1 : 1 - a) ^ d) {
  } else
    b = 0;
}

C35 : Crashes GCC 4.2.0 at -O1:

volatile int ***a;
int b;
int **c;
void
fn1 () {
  if (&c == a)
    b = 0 == *a;
}

C36 : Crashes GCC 4.2.0 at -O1:

struct S2 {
  volatile int f5:1;
  int f6
};
static struct S2 a;
void
main () {
  printf ("%d\n", a.f5);
}

C37 : Crashes GCC 4.3.0 at -O1:

long long *a;
int b;
void
fn1 () {
  long long **c = &a;
  int d = 7;
lbl_2890: {
    long long **e = &a;
    b = (e == c) < d;
    d = 0;
    goto lbl_2890;
  }
}

C38 : Crashes GCC 4.3.0 at -O2:

struct S2 {
  volatile int f5:1;
  int f6
};
static struct S2 a;
void
main () {
  printf ("%d\n", a.f5);
}

C39 : Crashes GCC 4.3.0 at -O3:

int a;
short b;
void
fn1 () {
  int c[0];
  for (;;) {
    a = c[0];
    b = 0;
    for (; b < 7; b += 1)
      c[b] = 0;
  }
}

C40 : Crashes GCC 4.3.0 at -O1:

volatile int **a;
int *b;
void
fn1 () {
  if (a == &b)
    **a;
}

C41 : Crashes GCC 4.3.0 at -O3:

int a, b, c, d, e, f;
void
fn1 () {
  char g;
lbl_120:
  if (b || e >= 0 & d >= 0 || a)
    return;
  g = f < 0 ? 1 : f;
  d = g == 0 || (char) f == 0 && g == 1 ? 0 : 0 % 0;
  if (c)
    goto lbl_120;
}

C42 : Crashes Intel CC 12.0.5 at -O1:

struct U0 {
  int f0
}
a;
struct U0
fn1 () {
  return a;
}
void
main () {
  0 > a.f0;
  fn1 ();
}

C43 : Crashes Open64 4.2.4 at -O3:

int a;
int *b;
unsigned c;
void
fn1 () {
  for (; a; a--)
    if (*b) {
      c = 0;
      for (; c >= 5; c++) {
      }
    }
}

C44 : Crashes Open64 4.2.4 at -O3:

short a;
void
fn1 () {
  long b;
  b = 44067713550;
  a |= b;
}

C45 : Crashes Open64 4.2.4 at -O3:

volatile int a;
void
fn1 () {
  int b = 1;
  a || b--;
}

C46 : Crashes Open64 4.2.4 at -O2:

int a, b;
void fn1 ();
void fn2 ();
void
fn3 () {
  fn2 ();
  fn1 ();
}
void
fn2 () {
  if (1) {
  } else
    for (;; b++) {
      int c = 0;
      int *d = &a;
      int **e = &d;
      *e = &c;
      *d = 0;
      *d |= 0;
    }
}

C47 : Crashes Open64 4.2.4 at -O3:

struct S0 {
  int f1:1
};
int a, b;
void
fn1 () {
  for (; b;) {
    struct S0 c = { };
    if (1) {
      c = c;
      a = c.f1;
    }
  }
}

C48 : Crashes Open64 4.2.4 at -O3:

int a, b;
int
fn1 () {
  int *c = &b;
  a = 0;
  for (; a >= -26; --a) {
    unsigned d = 18446744073709551615;
    int *e = &b;
    *e &= d;
  }
  return *c;
}

C49 : Crashes Open64 4.2.4 at -O3:

static int a, c, d;
int b;
int *e;
void
fn1 () {
  for (; a; a += 1) {
    b = 0;
    for (; b > -16; --b)
      for (; c;) {
        int *f = &d;
        *f = 0;
      } *e = 0;
  }
}

C50 : Crashes Sun CC 5.11 at -xO4:

unsigned char a, d;
struct {
  int f2
}
b;
int c, e;
void
fn1 (p1) {
}
void
fn2 () {
  c = 0;
  for (; c <= 0;)
    e = b.f2;
  fn1 (0);
  b = b;
  d = -a;
}

C51 : Crashes Sun CC 5.11 at -fast:

int a, c;
int b[1];
void
fn1 () {
  short d;
  for (; a; a -= 1) {
    d = b[c + 2] = b[c + 2];
    b[0] = 0;
  }
}

C52 : Crashes Sun CC 5.11 at -xO4:

int a, b, d;
short c;
int
fn1 (p1) {
  return a ? 0 : p1;
}
void
fn2 () {
  int e = 0;
  for (;;) {
    c = 0;
    d = fn1 (e ^ ~~c);
    d && b;
  }
}

C53 : Crashes Sun CC 5.11 at -fast:

long a;
int b, d;
int *c;
void
fn1 () {
  int *e;
  for (;; b--)
    for (; d;) {
      *c = 0;
      *c &= (&e != 1) / a;
    }
}

C54 : Crashes Sun CC 5.11 at -xO0:

#pragma pack(1)
struct {
  int f3:1;
  int f4:16
}
a = { 1, 0 };

C55 : Crashes Sun CC 5.11 at -xO3:

int a, c;
static int b = 1;
void fn1 ();
void
fn2 () {
  for (; a; a--) {
    c = 0;
    for (; c != 1;) {
      if (b)
        break;
      fn1 ();
    }
  }
}

C56 : Crashes Sun CC 5.11 at -xO4:

#pragma pack(1)
struct S0 {
  int f1;
  int f3:1
}
a;
void
fn1 (struct S0 p1) {
  p1.f3 = 0;
}
void
fn2 () {
  fn1 (a);
}

C57 : Crashes Sun CC 5.11 at -fast:

int a, c, d, e, f, g, h, i, j, k;
volatile int b;
int
fn1 () {
  for (; d; d = a) {
    int *l = &c;
    c = -3;
    for (; c > -23; --c)
      if (k) {
        if (*l)
          continue;
        return b;
      }
    for (; i; ++i) {
      j = 0;
      g = h;
      for (; f <= 1; f += 1) {
      }
    }
  }
  return e;
}