On Tue, Feb 6, 2018 at 1:37 PM, Dan Williams [off-list ref] wrote:

At that point we're basically just back to the array_ptr() version
that returned a sanitized pointer to an array element.

.. that one does an extra unnecessary 'andq' instead of the duplicated
cmp.  But at least it avoids comparing that 32-bit integer twice, so
it's probably slightly smaller.

(And your code generation is without the "r" -> "ir" fix for the size argument)

Probably doesn't matter. But a "asm goto" would give you at least
potentially optimal code.

            Linus