*:in x86-32 mode, it lost it in the x86-64 mode
It lost it before that. If you'll try to use segment with non-zero base address on Atom you'll see 4-5x slowdown. Other, larger, cores are not affected as much but still some operations become slower. AMD and Intel keep the segmentation supported for compatibility sake, but in reality it was already pushed to the slow-path before x86-64 was introduced. And situation is the same with fancy high-level instructions like BOUND. It's all uneven, of course: BOUND is fast on most AMD CPUs (may be on all, but I've not measured latest AMD creations) but it's fantastically slow on Intel CPUs.
That's what I'm talking about: fat is squeezed out of fast-path to raise CPU frequency.
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