Re: [PATCH 1/2] libgfortran: Remove early return if extent is zero [PR112371]

[Mikael Morin <morin-mikael@orange.fr>]

Le 06/11/2023 à 19:12, Harald Anlauf a écrit :
> Hi Mikael,
> 
> Am 06.11.23 um 12:43 schrieb Mikael Morin:
>> Remove the early return present in function templates for 
>> transformational
>> functions doing a (masked) reduction of an array along a dimension.
>> This early return, which triggered if the extent in the reduction 
>> dimension
>> was zero, was wrong because even if the reduction operation 
>> degenerates to
>> a constant value in that case, one has to loop anyway along the other
>> dimensions to initialize every element of the resulting array with that
>> constant value.
>>
>> The offending piece of code was present in several places, and this 
>> removes
>> them all.  Namely, the impacted m4 files are ifunction.m4 for regular
>> functions and types, ifunction-s.m4 for character minloc and maxloc, and
>> ifunction-s2.m4 for character minval and maxval.
> 
> I wonder if the correct fix would be to replace (instead of deleting)
> 
>> diff --git a/libgfortran/m4/ifunction.m4 b/libgfortran/m4/ifunction.m4
>> index c64217ec5db..480649cf691 100644
>> --- a/libgfortran/m4/ifunction.m4
>> +++ b/libgfortran/m4/ifunction.m4
>> @@ -232,8 +232,6 @@ m'name`'rtype_qual`_'atype_code` ('rtype` * const 
>> restrict retarray,
>>       }
>>
>>     len = GFC_DESCRIPTOR_EXTENT(array,dim);
>> -  if (len <= 0)
>> -    return;
>>
>>     mbase = mask->base_addr;
>>
> 
> by the following:
> 
>    if (len < 0)
>      len = 0;
> 
> See ifunction.m4, lines 56ff, which check if the result of
> 
>    len = GFC_DESCRIPTOR_EXTENT(array,dim);
> 
> is negative.  I haven't tried to create a testcase, though.
> 
> Similarly for the other templates.
> 

Yes, you're right.  I think I won't try to create a testcase and will 
just pick your suggestion which seems safer.