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Re: [patch, fortran] Handling of .and. and .or. expressions
Am 15. Juni 2018 19:49:42 MESZ schrieb Janne Blomqvist <blomqvist.janne@gmail.com>:
>On Fri, Jun 15, 2018 at 12:22 PM, Janus Weil <janus@gcc.gnu.org> wrote:
>
>> Am 14. Juni 2018 12:40:19 MESZ schrieb Janne Blomqvist <
>> blomqvist.janne@gmail.com>:
>> In Fortran, it still feels like functions as such are second-class
>> citizens. People seriously advise against using them. Doesn't really
>help
>> the attractivity of the language.
>
>
>Yes. Back when I followed c.l.f, several experts did advise people to
>never
>use functions unless they were pure (or more or less effectively so, if
>they didn't fulfill the standard requirements for purity). Considering
>that
>at least some of those same experts were also part of the Fortran
>standards
>committee, I just find it very strange that, to the best of my
>knowledge,
>no effort to fix this has been done.
Very strange indeed.
If someone tells me "don't use functions in Fortran", then what I hear is "don't use Fortran, it's broken".
Why would you introduce a language feature that is not meant to be used?
>IMHO it is completely insane to optimize out impure functions, just for
>a
>> little bit of speedup, but sacrificing compiler-independent results.
>>
>> I really don't understand why I'm so alone here with this opinion.
>>
>
>I would agree with you if there were some substantial majority opinion
>among Fortran programmers that all the parts of a logical expression
>are
>always evaluated
Look, in principle I don't really care how many parts of an expression are evaluated. If the compiler can prove that a certain part of the expression can not change the end result and has no side effects, great, please optimize it away. If the compiler can not prove that, the expression should not be altered. An 'optimization' that changes results is just not useful. It's broken.
Cheers,
Janus