[J3] lbound / ubound undefined behaviour?

[Robert Corbett]

The behavior is well-defined.

References herein are to J3/10-007r1 (Fortran 2008).  Subclause 7.2.1.3 paragraph 3 states the array is allocated with

 o if /expr/ is an array, the shape of the /expr/ with each lower bound equal to the corresponding element of LBOUND(/expr/).

Subclause 13.7.90 (LBOUND) says that in this case, the lower bounds have the value 1.  Therefore, the result is well-defined and is as described by A.

Robert Corbett

> On Jun 27, 2024, at 8:46 AM, Nathan Sircombe via J3 <j3 at mailman.j3-fortran.org> wrote:
> 
> 
> Hi,
>  
> I’ve got a question from one of the engineers in the compiler team here – I’d appreciate the J3 list’s opinion (actually some of the list are on the original fortran-lang thread).
>  
> The problem was initially discussed here: https://fortran-lang.discourse.group/t/an-interesting-difference-between-compilers/7131
> The initial conclusion seems to be that compilers from group "B” have the wrong end of the stick. But a separate discussion on the Flang github reached a different conclusion: https://github.com/flang-compiler/flang/issues/1435. Claiming that we are facing undefined behaviour and various compilers handle this situation differently.
> So, is it actually undefined behaviour and the compilers have liberty in handling it their own way? or it is clearly defined what the compilers should do?
>  
> Cheers,
> Nathan.
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