Hi Thomas,

Before answering that, I thought that I had better try the polyhedron suite
with -fwrapv and -std=legacy together. As far as I can see, all is well and
so, yes, I think that is a good idea.

Cheers

Paul

================================================================================
Date & Time     :  9 Mar 2023 18:13:04
Test Name       : gfor_13
Compile Command : gfc13 -ffast-math -funroll-loops -O3 -fwrapv -std=legacy
%n.f90 -o %n
Benchmarks      : ac aermod air capacita channel2 doduc gas_dyn2 fatigue2
induct2 linpk mp_prop_design nf protein rnflow test_fpu2 tfft2
Maximum Times   :    10000.0
Target Error %  :      0.100
Minimum Repeats :     1
Maximum Repeats :     2

   Benchmark   Compile  Executable   Ave Run  Number   Estim
        Name    (secs)     (bytes)    (secs) Repeats   Err %
   ---------   -------  ----------   ------- -------  ------
          ac      0.00       55904      7.17       2  0.0628
      aermod      0.00     1280104     10.77       2  1.2769
         air      0.00      136392      4.09       2  0.4276
    capacita      0.00      102680     23.79       2  0.7587
    channel2      0.00       43928    108.59       2  0.5834
       doduc      0.00      194224     13.98       2  0.2468
    gas_dyn2      0.00      104080    105.46       2  0.1659
    fatigue2      0.00       90752     62.86       2  1.3092
     induct2      0.00      224920     58.08       2  0.6594
       linpk      0.00       51768      7.15       2  0.4892
mp_prop_desi      0.00       48432     94.28       2  0.0164
          nf      0.00       64480     11.16       2  0.0134
     protein      0.00      140592     24.22       2 10.0347
      rnflow      0.00      197704     20.74       2  0.1904
   test_fpu2      0.00      147232     53.54       2  0.1093
       tfft2      0.00       43896     55.09       2  3.8688

Geometric Mean Execution Time =      26.19 seconds

================================================================================

On Thu, 9 Mar 2023 at 17:30, Thomas Koenig <tkoenig@netcologne.de> wrote:

> Hi Paul,
>
>
> > -fdefault-integer-8 does indeed fix the problem with
> > rnflow.f90 but breaks tfft2.f90, with a type mismatch at lines 36 and 44.
> >
> >        integer(8), parameter   :: jmul =  843314861  ! multiplicateur
> >        integer(8), parameter   :: jadd =  453816693  ! constante additive
> > Does the job and is portable.
> >
>
> I think -frwapv (as suggested by Jakub) would be the better choice.
> The problem is the linear congruential pseudo-random number generators
> which were much used in earlier times (and are still present in
> legacy code), which violate the Fortran standards by assuming silent
> truncation.
>
> If a new optimization breaks this (widespread, but illegal) idiom,
> maybe the best way to deal with it is to add -frwapv to -std=legacy.
>
> What do you think?
>
> Best regards
>
>         Thomas
>


-- 
"If you can't explain it simply, you don't understand it well enough" -
Albert Einstein