[robinsonb5]

The problem is that what the machine does isn't necessarily consistent. If you're using old-as-the-green-hills integer instructions then yes, the CPU supports unaligned access. If you want to benefit from the speedup afforded by the latest vector instructions, now it suddenly it doesn't.

Also, to be fair, GCC does appear to back off the optimisations when dealing with, for example, a struct with the packed attribute.

[saagarjha]

That depends on which vector instructions you use.