On 20/02/2021 13.49, Uecker, Martin wrote:
> Am Samstag, den 20.02.2021, 12:44 +0100 schrieb Jens Maurer:

>> Right, but notice that in the above example, the address
>> isn't actually taken at run-time (note "if (false)"), yet
>> this vacuous code appears to have semantic effect
>> throughout the function.
>
> The rule refers to a static property (could
> be declared as register) and not the run-time
> effect of taking the adress.

Yes, but that's not a good rule in my view.

For example, if the function is longer, there
might be sections of the function where the
value can be kept in a register (because no
address is taken in the vicinity), and the value
is materialized into memory only around the
place and time where/when the address is taken.
This optimization approach seems to be precluded,
because the value has to be put in memory
right away (assuming a suitable architecture
where all this matters in the first place,
of course).

>> Is there any other case
>> similar to that, where non-executed syntactically
>> well-formed code has an effect throughout the entire
>> function? I can't think of any.
>
> True, also I do not see why this is a problem.
>
> I like how the rules makes many use cases just
> work: In all cases where code would work
> byte-wise on an object you would take the
> address first. For all typical local variables
> you get undefined behavior.

In my view, we have a syntax-based rule in C
that is overbroad.

Jens