🚀 go-pugleaf

In article <BtnI48.D9I@twwells.com> bill@twwells.com (T. William Wells) writes:
> The problem is then what to do with statements like a; and a=b;
> when a is a volatile object. The first expression accesses a but
> then discards the value, which is fine. The other does NOT do
> what you'd expect, though. The reason is that the assignment has a
> value which is the value of a after the assignment, which can only
> be obtained by accessing a. Thus a=b results in a sequence like:
>
>	load b
>	store a
>	load a
>
> rather than the intended load and store.

Here's the mistake. The value of the expression can be obtained by
remembering the value stored into a - it is not necessary to re-fetch
it, even though a is volatile.

The storing of a value into a is a side-effect, and so takes place
sometime before the next sequence point. Any other change that takes
place to a (e.g. because it is a memory-mapped device) between the same
pair of sequence points counts as a double assignment, and is therefore
undefined, and therefore the implementation can do what it wants
(including not reading a after storing).

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