[Bug tree-optimization/18754] New: unrolling happens too late/SRA does not happen late enough

[pinskia at gcc dot gnu dot org]

Take the following code:
struct X { float array[4]; };

X a,b;

float foobar () {
  float s = 0;
  X c;
  for (unsigned int d=0; d<4; ++d)
    c.array[d] = a.array[d] * b.array[d];
  for (unsigned int d=0; d<4; ++d)
    s+=c.array[d];
  return s;
}

With -O3 -funroll-loops -fno-ivopts -ffast-math (the fno-ivopts is because 
there are some ADDR_EXPR 
which we don't mark as invariant/constant which I will file in another bug) we 
get in .vars:
  c.array[0] = a.array[0] * b.array[0];
  c.array[1] = a.array[1] * b.array[1];
  c.array[2] = a.array[2] * b.array[2];
  D.1572 = a.array[3] * b.array[3];
  c.array[3] = D.1572;
  return D.1572 + c.array[0] + c.array[1] + c.array[2];

Note how we could SRA c.array.

-- 
           Summary: unrolling happens too late/SRA does not happen late
                    enough
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Keywords: missed-optimization, TREE
          Severity: enhancement
          Priority: P2
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: pinskia at gcc dot gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18754