[Bug tree-optimization/29145] New: unsafe use of restrict qualifier

[djg at cray dot com]

In the test case below, GCC doesn't observe a non-restrict-qualified
pointer being "based on" a restrict-qualified pointer. On i686-pc-linux-gnu, 
this program aborts when compiled with
-O2 -msse -ftree-vectorize
because the loop in function with_restrict is vectorized based on an unsafe
alias assumption.

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

void with_restrict(int * __restrict p)
{
  int i;
  int *q = p - 2;

  for (i = 0; i < 1000; ++i) {
    p[i] = q[i];
  }
}

void without_restrict(int * p)
{
  int i;
  int *q = p - 2;

  for (i = 0; i < 1000; ++i) {
    p[i] = q[i];
  }
}

int main(void)
{
  int i;
  int a[1002];
  int b[1002];

  for (i = 0; i < 1002; ++i) {
    a[i] = b[i] = i;
  }

  with_restrict(a + 2);
  without_restrict(b + 2);

  for (i = 0; i < 1002; ++i) {
    if (a[i] != b[i])
      abort();
  }
  exit(0);
}


-- 
           Summary: unsafe use of restrict qualifier
           Product: gcc
           Version: 4.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: djg at cray dot com
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29145