vectorization of non consecutive data-accesses

[Fahimeh Yazdanpanah <fahim_yazdan@xxxxxxxxx>]

Hello,

I used gcc for vectorization of non consecutive data-accesses.

Using gcc-4.3.3 and these flags, -O3  -ftree-vectorize -ftree-vectorizer-verbose=20 -ffast-math -mfpmath=sse -march=core2, I compiled the following loops hopefully to vectorized:

for (i = 0; i < N/2; i++){
  a[i] = b[2*i+1] * c[2*i+1] - b[2*i] * c[2*i];
  d[i] = b[2*i] * c[2*i+1] + b[2*i+1] * c[2*i];
}

for (i = 0; i < N; i+=4){
  a[i]=b[i];

but these loops were not vectorized. Please tell me what I did wrong?
   

Thanks a lot,
Fahimeh