title: Strange gcc6.1 -O2 compiling behaviour
body: <p>I am compiling the same benchmark using gcc <code>-O2 -march=native</code> flags. However, Interesting thing is when I look at the <code>objdump</code>, it actually produce some instructions like <code>vxorpd</code>, etc, which I think should only appear when <code>-ftree-vectorize</code> is enabled (and <code>-O2</code> should not enable this by default?) If I add <code>-m32</code> flag to compile in 32 bit instruction, these packed instructions disappeared. Anyone met similar situations could give some explanations? Thanks.</p>