On 20/02/2021 12.27, Uecker, Martin wrote:
> Am Samstag, den 20.02.2021, 12:10 +0100 schrieb Jens Maurer:
>> The "could have been declared with register" rule in C
>> doesn't seem friendly either, because a seemingly benign
>> no-op has spooky effects at a distance:
>>
>> void f()
>> {
>> int i;
>>
>> [... some lines of code...]
>>
>> if (false)
>> (void)&i; // ah, address was taken, go back to the beginning of "f" and re-analyze all the
>> code
>> }
>
> Compilers need to track anyway whether the address was
> taken so this information is readily available. Also
> initialization and use can be at a distance, so deciding
> whether a variable is (potentially) read before
> initialization is a global property of a function anyway.

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. 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.

Jens