Auto vectorization not working

Question

I\'m trying to get my code to auto vectorize, but it isn\'t working.

int _tmain(int argc, _TCHAR* argv[])
{
    const int N = 4096;
    float x[N];
    float         


        

Answer 1

One problem could be that your stack allocation isn't necessarily aligned by your compiler. If your compiler supports c++11 you could use:

float x[N] alignas(16);
float y[N] alignas(16);

To explicitly get 16 byte aligned memory, which is required by most SSE operations.

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EDIT:

Even if alignment isn't the issue and your compiler is vectorizing unaligned code you should make this optimization as unaligned SSE operations are very slow compared to their aligned counterparts.