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Subject: [Bug c/32575] [4.2/4.3 regression] With -ftree-vrp miscompiles a single line of code in SQLite
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------- Comment #4 from jakub at gcc dot gnu dot org  2007-08-28 14:55 -------
On the trunk I'm just seeing
*** in database main ***
Page 2 is never used
That seems to be because of miscompiled sqlite3SelectNew function with
-O2 -fstrict-aliasing, with -O2 -fno-strict-aliasing that works.

Here is a reduced self-contained testcase for that:

extern void abort (void);

struct S
{
  void *s1;
  unsigned char s2, s3, s4, s5, s6, s7;
  char s8;
  void *s9, *s10, *s11, *s12, *s13;
  struct S *s14, *s15;
  void *s16, *s17;
  int s18, s19, s20[3];
};

__attribute__((noinline))
void *foo (int x, int y)
{
  static struct S s;
  if (x != sizeof (struct S) || y != 1)
    abort ();
  return &s;
}

__attribute__((noinline))
void bar (struct S *p)
{
  asm volatile ("" : "=m" (*p) : "m" (*p));
}

__attribute__((noinline))
void *baz1 (void *x, void *y,void *z)
{
  if (y || z)
    abort ();
  return x;
}

__attribute__((noinline))
void *baz2 (int x, void *y, void *z, void *a)
{
  if (x || y || z || a)
    abort ();
  return (void *) 0;
}

__attribute__((noinline))
struct S *test (void *a, void *b, void *c, void *d, void *e, void *f, int g,
void *h, void *i)
{
  struct S *p, q;
  p = foo (sizeof (*p), 1);
  if (p == 0)
    {
      p = &q;
      __builtin_memset (p, 0, sizeof (*p));
    }
  if (a == 0)
    a = baz1(0, baz2(107,0,0,0), 0);
  p->s1 = a;
  p->s9 = b;
  p->s10 = c;
  p->s11 = d;
  p->s12 = e;
  p->s13 = f;
  p->s3 = g;
  p->s2 = 110;
  p->s16 = h;
  p->s17 = i;
  p->s18 = -1;
  p->s19 = -1;
  p->s20[0] = -1;
  p->s20[1] = -1;
  p->s20[2] = -1;
  if (p == &q)
    {
      bar(p);
      p = 0;
    }
  return p;
}

int
main (void)
{
  int a;
  int b;
  struct S *z = test ((void *) &a, (void *) &b, 0, 0, 0, 0, 0, 0, 0);
  if (z == 0)
    abort ();
  if (z->s1 != (void *) &a || z->s2 != 110 || z->s3 || z->s4)
    abort ();
  if (z->s5 || z->s6 || z->s7 || z->s8)
    abort ();
  if (z->s9 != (void *) &b || z->s10 || z->s11 || z->s12)
    abort ();
  if (z->s13 || z->s14 || z->s15 || z->s16)
    abort ();
  if (z->s17 || z->s18 != -1 || z->s19 != -1)
    abort ();
  if (z->s20[0] != -1 || z->s20[1] != -1 || z->s20[2] != -1)
    abort ();
  return 0;
}


-- 

jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|GCC 4.2.0 with -ftree-vrp   |[4.2/4.3 regression] With -
                   |miscompiles a single line of|ftree-vrp miscompiles a
                   |code in SQLite              |single line of code in
                   |                            |SQLite


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32575