Should unreachable code be considered an error?

[Don]

Sean Kelly wrote:
> Was this broken condition something that could have been detected statically?  I've encountered plenty of broken conditions, but I've never had a compiler correctly flag one such.

Yes.

if (a > C1 && a < C2) ...

where C1, C2 are compile-time constants, and C1 > C2.
(correct condition was: a > C2 && a < C1)

> 
> Sent from my iPhone
> 
> On Aug 21, 2011, at 12:39 PM, Don <nospam at nospam.com> wrote:
> 
>> Sean Kelly wrote:
>>> On Aug 18, 2011, at 10:29 AM, Nick Sabalausky wrote:
>>>> "Bernard Helyer" <b.helyer at gmail.com> wrote in message news:j2ithq$12kd$1 at digitalmars.com...
>>>>> I asked the Ars forums ( http://arstechnica.com/civis/viewtopic.php?
>>>>> f=20&t=1153378&p=21965411 ) and I ask the same of you: should
>>>>> unambiguously unreachable code be an error or a warning? ( see the linked
>>>>> forum post for more details ).
>>>> No. That would be a royal pain in the ass during debugging. I expect to be able to stick a "return xxxx;" anywhere I want to test something and not have the compiler crap out because I didn't deal with the overhead of commenting out the rest.
>>>>
>>>> A warning might be nice, though.
>>> A warning if anything.  I've never encountered a situation where code was made unreachable by accident.  I also get "unreachable code" warnings periodically, for code that is absolutely reachable.  I don't want my code to not compile simply because the compiler can't perform adequate flow analysis.
>> I have encountered bugs of the form:
>> if (cond) { /* unreachable */ }
>> and the cond was unintentionally always false. The last time I encountered such a bug was last week. I'm surprised your experience is so different.
>>
>> It's crucial that it should never report "unreachable" if it is unsure (not even a warning).
>> But I think conditional compilation is a huge problem -- code may be valid under different compilation conditions. I suspect that to eliminate all the false positives, it'd have to be so conservative, that it wouldn't catch any bugs.
>>