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Previous ARM generations had a "strongly ordered" memory type. ARMv8 doesn't have this for cacheable memory (normal) but device memory has a R(erorder) attribute to control access ordering. Of course device memory isn't cached either. Beyond that the non reordering attribute only applies within an implementation defined block size and its behavior with respect to normal accesses (or outside the block) isn't defined either. Making it mostly useless except for the most restrictive of cases.

https://news.ycombinator.com/item?id=14319420

Not sure where MikusR gets this info from, but it could be right given that Snapdragon 820 is Qualcomm's custom core.

While I consider this explanation as interesting and plausible, it is a patent by IBM and not by Qualcomm (there can still license agreements negotiated etc.).