[Bug tree-optimization/62171] New: restrict pointer to struct with restrict pointers parm doesn't prevent aliases

["vries at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62171

            Bug ID: 62171
           Summary: restrict pointer to struct with restrict pointers parm
                    doesn't prevent aliases
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vries at gcc dot gnu.org

Created attachment 33351
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=33351&action=edit
test-case, derived from testcase for PR46032

The test-case (attached) contains a function parameter with type restrict
pointer to struct with restrict pointers:
...
struct omp_data_i
{
  double *__restrict__ results;
  double *__restrict__ pData;
  double *__restrict__ coeff;
};

static double __attribute__((noinline, noclone))
f (struct omp_data_i *__restrict__ p, int argc)
{

  int idx;

  for (idx = 0; idx < nEvents; idx++)
    ((p->results))[idx] = (*(p->coeff)) * ((p->pData))[idx];

  return ((p->results))[argc];
}
...

Despite using restrict, we don't manage to get rid of the aliases:
...
$ gcc test.c -O2 -ftree-vectorize -fdump-tree-vect-all
$ egrep 'note: vectorized|version' test.c.*.vect
test.c:15:3: note: versioning for alias required: can't determine dependence
between *pretmp_35 and *_8
test.c:15:3: note: versioning for alias required: can't determine dependence
between *_12 and *_8
cost model: Adding cost of checks for loop versioning aliasing.
test.c:15:3: note: created 2 versioning for alias checks.
test.c:15:3: note: loop versioned for vectorization because of possible
aliasing
test.c:11:1: note: vectorized 1 loops in function.
...

Rewriting the example such that it has seperate function parameters with type
restrict pointer fixes the problem. 

Rewriting the example such that it has seperate function parameters with type
restrict pointer to restrict pointer fixes the problem. 

Rewriting the example such that it has as parameter a single struct with
restrict pointers fixes the problem.