Re: dead code or otherwise, was Alternative C compilers on x86_64 Linux?

On Tue, 6 Sep 2016 21:35:30 +0100, BartC <bc@freeuk.com> wrote:


>On 06/09/2016 03:15, Kaz Kylheku wrote:
>
>> A duplicate condition in an if-else chain is unreachable code, which is
>> probably a bug.
>>
>> if (foo) {
>> ...
>> } else if (foo) {
>> /* unreachable */
>> } else if (bar) {
>> ...
>> }
>
>It's not necessarily unreachable. For example:
>
> if (foo()) { ...}
> elsif if (foo()) { ... }
>
>foo() could return false the first time and true the second time.


In such cases foo doesn't need to be function - it only needs to be a
[moral equivalent of a C] volatile to exhibit strange behavior.


Writing an IF chain with multiple identical tests probably should be a
style warning in and of itself.




>In general detecting duplication conditions for if-else can involve
>comparing expressions of arbitrary complexity, and it can be harder to
>determine if they will always yield the same value.


Yes. It's infeasible in most circumstances.


George

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