Re: [PATCH 09/10] fortran: Support clobbering of variable subreferences [PR88364]

[Harald Anlauf <anlauf@gmx.de>]

Am 19.09.22 um 22:50 schrieb Mikael Morin:
> Le 19/09/2022 à 21:46, Harald Anlauf a écrit :
>> Am 18.09.22 um 22:55 schrieb Mikael Morin:
>>> Le 18/09/2022 à 20:32, Harald Anlauf a écrit :
>>>>
>>>> Assumed shape will be on the easy side,
>>>> while assumed size likely needs to be excluded for clobbering.
>>>>
>>> Isn’t it the converse that is true?
>>> Assumed shape can be non-contiguous so have to be excluded, but assumed
>>> size are contiguous, so valid candidates for clobbering. No?
>>
>> I really was referring here to *dummies*, as in the following example:
>>
>> program p
>>    integer :: a(4)
>>    a = 1
>>    call sub (a(1), 2)
>>    print *, a
>> contains
>>    subroutine sub (b, k)
>>      integer, intent(in)  :: k
>>      integer, intent(out) :: b(*)
>> !   integer, intent(out) :: b(k)
>>      if (k > 2) b(k) = k
>>    end subroutine sub
>> end program p
>>
>> Assumed size (*) is just a contiguous hunk of memory of possibly
>> unknown size, which can be zero.  So you couldn't set a clobber
>> for the a(1) actual argument.
>>
> Couldn't you clobber A entirely?  If no element of B is initialized in 
> SUB, well, A has undefined values on return from SUB.  That's how 
> INTENT(OUT) works.
> 

I think I understand much of what is said, but I feel that I do
not really understand what *clobber* means for the different
beasts we are discussing (although I have an impression of what
it means for a scalar object).