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Re: [patch, fortran] Handling of .and. and .or. expressions
Am 14. Juni 2018 11:41:03 MESZ schrieb Janne Blomqvist <blomqvist.janne@gmail.com>:
>On Thu, Jun 14, 2018 at 11:38 AM, Janus Weil <jaydub66@gmail.com>
>wrote:
>
>>
>> Am 14. Juni 2018 10:05:24 MESZ schrieb Janne Blomqvist <
>> blomqvist.janne@gmail.com>:
>>
>> >Either
>> >
>> >a) short-circuiting in left-to-right order
>> >
>> >or
>> >
>> >b) must evaluate all the arguments in left-to-right order
>> >
>> >My preference would be for a) as that is what most languages are
>doing,
>>
>> Well, C/C++ has two different kinds of operators that give you the
>choice
>> to specify whether you want short-circuiting or not.
>
>Presumably you're thinking of "&" and "|". But to be pedantic, those
>are
>bitwise operators, not non-short-circuiting boolean operators
Yes, but they work perfectly fine as logical operators on booleans, don't they?
>There are however situations where
>they are not equivalent to hypothetical non-short-circuiting boolean
>operators!
Could you give a simple example of such a case?
>>but
>> >even b) would be better than leaving it undefined.
>>
>> Agreed.
>>
>> In my opinion the best strategy for gfortran in the current situation
>> would be to apply short-circuiting whenever it can be proven that it
>has no
>> observable consequences. E.g. a function call should not be optimized
>away
>> unless it is pure.
>
>Hmm, why? I don't see why always evaluating everything is less wrong
>than
>short-circuiting?
I'm not saying it is "less wrong", but it can be less efficient. In that sense my proposed strategy is a compromise that tries to avoid harmful optimizations but still does optimization where it is safe.
Cheers,
Janus