Memory barrier for fat initialization

[Torbjörn Granlund]

This article summarises things well.  The x86/AMD64 indeed only reorders
load before stores (except under the obscure OOStore mode).

http://www.rdrop.com/users/paulmck/scalability/paper/ordering.2007.09.19a.pdf

There is some reasoning about the weaker ordering of some SSE
instructions, as well as references to definitive Intel/AMD
documentation.

-- 
Torbjörn
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