[Bug tree-optimization/34195] New: missed optimization with store motion (vectorizer)

[eres at il dot ibm dot com]

The following loop does not get vectorized 
on powerpc64-linux, r130275, GCC 4.3.0:

#define M 10

struct S
{
  float x;
  float y;
} pS[100];

float a[1000];
float b[1000];

void
foo (int n)
{
  int i, j;

  for (i = 0; i < n; i++)
    {
      pS[i].x = 0;
      pS[i].y = 0;

      for (j = 0; j < M; j++)
        {
          pS[i].x += (a[i]+b[i]);
          pS[i].y += (a[i]-b[i]);
        }
    }
}

Here is a snippet from the vectorizer dump file:

u3.c:17: note: dependence distance modulo vf == 0 between pS[i_37].x and
pS[i_37].x
u3.c:17: note: dependence distance  = 0.
u3.c:17: note: accesses have the same alignment.
u3.c:17: note: dependence distance modulo vf == 0 between pS[i_37].y and
pS[i_37].y
u3.c:17: note: === vect_analyze_data_ref_accesses ===
u3.c:17: note: Detected interleaving of size 2
u3.c:17: note: not vectorized: complicated access pattern.
u3.c:17: note: bad data access.(get_loop_exit_condition

...

        base_address: &pS
        offset from base address: (<unnamed-signed:32>) ((unsigned int) i_37 *
8)
        constant offset from base address: 0
        step: 0
        aligned to: 8
        base_object: pS[0].x
        symbol tag: pS
        FAILED as dr address is invariant

u3.c:22: note: not vectorized: unhandled data-ref
u3.c:22: note: bad data references.
u3.c:14: note: vectorized 0 loops in function.

[Zdenek's patch which extends lim can help to do store motion and thus help to
the vectorizer - http://gcc.gnu.org/ml/gcc-patches/2007-01/msg02331.html, but
AFAICT it is not applicable to current mainline)]


-- 
           Summary: missed optimization with store motion (vectorizer)
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: eres at il dot ibm dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34195