[QE-developers] Fortran features support in QE code

[Ye Luo]

Languages have ISO standards.
The maturity of compiler implementations of a language standard is very
important when adopting.
This a page summarizing compiler support of fortran 2008
http://fortranwiki.org/fortran/show/Fortran+2008+status
The BLOCK construct is a hole for PGI compiler even in 2018 release which
claimed a F2003 compiler.
Other compilers like GNU, INTEL, IBM should support 2008 already.

BLOCK is designed to provide the effect of scoping and you are allowed to
declare variables locally instead of in the beginning.
I think this helps compilers to identify locality and make optimization
more efficient. It also helps the code readability.

Some additional comment,
QE manual says "you need C and Fortran-90/95/2003 compilers". This is a
very vague statement.
It doesn't make sense to compile part in F95 and part in F2003 and it is
also not necessary.
For C it needs at least C89,
For Fortran, it needs F2003 if hdf5 is turned on.
For this reason, I think having F2003 as a baseline is fine for QE since
F2003 is fully supported by major compilers.

Ye

===================
Ye Luo, Ph.D.
Leadership Computing Facility
Argonne National Laboratory

2018-03-14 16:40 GMT-05:00 Paolo Giannozzi <p.giannozzi at gmail.com>:

> There are no exact rules. My opinion is that only language features that
> are well supported by most important compilers since at least a few years
> (let us say 5) should be included. What are those "blocks" good for?
>
> Paolo
>
> On Wed, Mar 14, 2018 at 5:39 PM, Miguel Carvajal <
> krvajal.miguelangel at gmail.com> wrote:
>
>> Hello,
>> is it possible to use this block constructor in the QE code,
>> https://www.ibm.com/support/knowledgecenter/en/SS2MB5_14.1.
>> 0/com.ibm.xlf141.bg.doc/language_ref/blockcon.html
>> or it is forbidden to maintain compatibility with old browsers?
>>
>>
>>
>> *Miguel Carvajal*   PhD
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>
>
> --
> Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
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