[Bug tree-optimization/20601] New: [4.0 Regression] PRE related miscompilation

[jakub at gcc dot gnu dot org]

extern void abort (void);
extern void exit (int);

struct T
{
  char *t1;
  char t2[4096];
  char **t3;
};

int a[5];
int b;
char **c;
int d;
char **e;
struct T t;
char *f[16];
char *g[] = { "a", "-u", "b", "c" };

__attribute__ ((__noreturn__)) void
foo (void)
{
  while (1);
}

__attribute__ ((noinline)) char *
bar (char *x, unsigned int y)
{
  return 0;
}

static inline char *
baz (char *x, unsigned int y)
{
  if (sizeof (t.t2) != (unsigned int) -1 && y > sizeof (t.t2))
    foo ();
  return bar (x, y);
}

static inline int
setup1 (int x)
{
  char *p;
  int rval;

  if (!baz (t.t2, sizeof (t.t2)))
    baz (t.t2, sizeof (t.t2));

  if (x & 0x200)
    {
      char **h, **i = e;

      ++d;
      e = f;
      if (t.t1 && *t.t1)
        e[0] = t.t1;
      else
        abort ();

      for (h = e + 1; (*h = *i); ++i, ++h)
        ;
    }
  return 1;
}

static inline int
setup2 (void)
{
  int j = 1;

  e = c + 1;
  d = b - 1;
  while (d > 0 && e[0][0] == '-')
    {
      if (e[0][1] != '\0' && e[0][2] != '\0')
        abort ();

      switch (e[0][1])
        {
        case 'u':
          if (!e[1])
            abort ();

          t.t3 = &e[1];
          d--;
          e++;
          break;
        case 'P':
          j |= 0x1000;
          break;
        case '-':
          d--;
          e++;
          if (j == 1)
            j |= 0x600;
          return j;
        }
      d--;
      e++;
    }

  if (d > 0 && !(j & 1))
    abort ();

  return j;
}

int
main (void)
{
  int x;
  c = g;
  b = 4;
  x = setup2 ();
  t.t1 = "/bin/sh";
  setup1 (x);
  if ((x & 0x400) && !a[4])
    abort ();
  exit (0);
}

is miscompiled on at least i386, x86_64 and ppc32 at -O2 (but e.g. on ppc64
is not).  The bug goes away with -O2 -fno-tree-pre.
At *.crited there is still:
xD.1586_12 = PHI <1537(10), xD.1586_61(38), xD.1586_2(28), xD.1586_128(27)>;
later on used by
x.0D.1645_38 = (unsigned intD.3) xD.1586_12;
...
  D.1589_46 = x.0D.1645_38 >> 10;
  D.1590_47 = (intD.0) D.1589_46;
  D.1591_48 = D.1590_47 & 1;
  if (D.1591_48 != 0) goto <L40>; else goto <L66>;

1537 == 0x601 is one of the possible values for x, if g contained say "--"
as second argument, but it is certainly not the only one (x should be 1 with
the g array provided in the testcase).
Yet PRE decides to use 0x601, so the
  if ((x & 0x400) && !a[4])
    abort ();
test aborts.

-- 
           Summary: [4.0 Regression] PRE related miscompilation
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: critical
          Priority: P2
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jakub at gcc dot gnu dot org
                CC: dberlin at gcc dot gnu dot org,gcc-bugs at gcc dot gnu
                    dot org
GCC target triplet: i386-linux, x86_64-linux, ppc-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20601