Consider the following short function:

    void Tst1(float* __restrict__ SrcP, float* __restrict__ DstP, int Len)
    {
        for (int x=0; x<Len; x++)
        {
            DstP[x] = SrcP[x] * SrcP[x];
        }
    }

If this function is compiled with:
    g++41 -O -S TstPow.cpp -ftree-vectorizer-verbose=5  -ftree-vectorize
it is vectorized, but if you compile with:
    g++41 -O -ffast-math -S TstPow.cpp -ftree-vectorizer-verbose=5
    -ftree-vectorize
it is not with the following output:

note: Vectorizing an unaligned access.
note: Alignment of access forced using peeling.
note: not vectorized: stmt not supported: D.2052_15 = __builtin_powf 
(D.2051_14, 2.0e+0)
note: vectorized 0 loops in function.


Michael Cieslinski