[bug #50270] Article "Problems with reordering code" misleading

[Marcin Godlewski]

Follow-up Comment #10, bug #50270 (project avr-libc):

Well, as already proposed 3 years ago, the below sentences:

memory barriers ensure proper ordering of volatile accesses
memory barriers don't ensure statements with no volatile accesses to be
reordered across the barrier

may be replaced with:

memory barriers ensure proper ordering of global variables accesses
memory barriers don't ensure local variables accesses to be reordered across
the barrier

or if the word "global" and "local" are not accurate, maybe this way:

memory barriers ensure proper ordering of global variables accesses
(as every global variable is possibly a subject of sharing across different
execution contexts)
memory barriers don't ensure automatic variables accesses to be reordered
across the barrier
(as by definition, automatic variables cannot be shared across different
execution contexts)

I would also propose to add a note, that applying a memory barrier is a way of
ordering memory accesses and not a way of ordering general code execution.

Please treat this as a starting point of the discussion. Hopefully we can
achieve an agreement on new wording. The article conclusion is at least
strongly misleading and really requires an update. 

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