[Bug tree-optimization/27285] New: [4.1 regression] ivopts postgresql miscompilation

["jakub at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

extern void abort (void);

struct S { unsigned char a, b, c, d[16]; };

void __attribute__ ((noinline))
foo (struct S *x, struct S *y)
{
  int a, b;
  unsigned char c, *d, *e;

  b = x->b;
  d = x->d;
  e = y->d;
  a = 0;
  while (b)
    {
      if (b >= 8)
        {
          c = 0xff;
          b -= 8;
        }
      else
        {
          c = 0xff << (8 - b);
          b = 0;
        }

      e[a] = d[a] & c;
      a++;
    }
}

int
main (void)
{
  struct S x = { 0, 25, 0, { 0xaa, 0xbb, 0xcc, 0xdd }};
  struct S y = { 0, 0, 0, { 0 }};

  foo (&x, &y);
  if (x.d[0] != y.d[0] || x.d[1] != y.d[1]
      || x.d[2] != y.d[2] || (x.d[3] & 0x80) != y.d[3])
    abort ();
   return 0;
}

On i686-linux with -O2 -m32 the loop is miscompiled, it copies over just
first 24 bits and not the 25th bit.  From quick skimming of the tree dumps,
this looks messed up by ivopts pass.  Seems to be a recent regression,
at least 20060304 GCC 4.1.x worked fine, while 20060420 does not.


-- 
           Summary: [4.1 regression] ivopts postgresql miscompilation
           Product: gcc
           Version: 4.1.1
            Status: UNCONFIRMED
          Severity: critical
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jakub at gcc dot gnu dot org
GCC target triplet: i686-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27285