[Bug c/21212] New: missed vectorization opportunity

[hurbain at cri dot ensmp dot fr]

The frontend translates this function:

void test_loop_c(char a[16], char b[16], char c[16])
{
  int i;

  for(i = 0; i<16; i++)
    {
      c[i] = a[i] + b[i];
    }
}

to 
{
  int i;

    int i;
  i = 0;
  goto <D2143>;
  <D2142>:;
  *(c + (char *) (unsigned int) i) = (char) ((signed char) *(a + (char *)
(unsigned int) i) + (signed char) *(b + (char *) (unsigned int) i));
  i++ ;
  <D2143>:;
  if (i <= 15) goto <D2142>; else goto <D2144>;
  <D2144>:;
}

and therefore misses an opportunity for vectorization (e.g. paddb from SSE2)
because the table is accessed by pointers and the dependance analysis does not
work in the loop.
Note that GCC vectorizes the same code, with a, b and c defined as global
variables as expected.

-- 
           Summary: missed vectorization opportunity
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: hurbain at cri dot ensmp dot fr
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21212