[Bug tree-optimization/26745] New: Simple loop is no longer vectorized

[micis at gmx dot de]

The gcc40 was able to vetorize the simple program given below, gcc41 and gcc42
are failing to vectorize with the message:

novect.cpp:21: note: not vectorized: can't determine dependence between
A_4->X[f_9] and C_8->X[f_9]
novect.cpp:21: note: vectorized 0 loops in function.

Michael Cieslinski


<novect.cpp>
struct S
{
    enum {count = 40};

    typedef struct { double X[count]; } __attribute__(( aligned(16) )) DblAli;

    struct {double X[count];} aaa __attribute__(( aligned(16) ));
    struct {double X[count];} bbb __attribute__(( aligned(16) ));
    struct {double X[count];} ccc __attribute__(( aligned(16) ));

    void Func ();
} __attribute__(( aligned(16) ));


void S::Func ()
{
    DblAli* __restrict__ A = (DblAli*)(&aaa.X[0]);
    DblAli* __restrict__ B = (DblAli*)(&bbb.X[0]);
    DblAli* __restrict__ C = (DblAli*)(&ccc.X[0]);

    for (int f=0; f<count; f++)
    {
        (*C).X[f] = (*A).X[f] * (*B).X[f];
    }
}


-- 
           Summary: Simple loop is no longer vectorized
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: micis at gmx dot de
 GCC build triplet: x86_64-unknown-linux-gnu
  GCC host triplet: x86_64-unknown-linux-gnu
GCC target triplet: x86_64-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26745