[Patch, Fortran] PR 78392: ICE in gfc_trans_auto_array_allocation, at fortran/trans-array.c:5979

[Janus Weil]

Hi all,

I hate to ping this patch once more, but somehow we need to come to a
conclusion here.

The issue boils down to the fact that there is a piece of code in the
gfortran code which claims that specification functions are
'constant', but I doubt that this is true. To my understanding the
concept of specification expressions and specification functions (see
section 7.1.6 in the F03 standard) was introduced essentially to refer
to side-effect-free expressions that can be used e.g. in a
type-specification context (array bounds, char-length parameters etc).

However I think 'specification functions' do not necessarily need to
be 'constants', in the sense that subsequent invocations give always
the same (constant) result and their value can be determined at
compile time.

My patch is at: https://gcc.gnu.org/ml/fortran/2016-11/msg00188.html
Further discussion at: https://gcc.gnu.org/ml/fortran/2016-11/msg00243.html

Any comments, please!?!

Cheers,
Janus



2016-12-03 8:05 GMT+01:00 Janus Weil <janus@gcc.gnu.org>:
> double-ping!
>
>
> 2016-11-26 10:45 GMT+01:00 Janus Weil <janus@gcc.gnu.org>:
>> ping!
>>
>>
>> 2016-11-19 10:12 GMT+01:00 Janus Weil <janus@gcc.gnu.org>:
>>> Hi all,
>>>
>>>> I previously assumed that the test case for this PR would be legal,
>>>> but by now I think that's wrong. The test case should be rejected, and
>>>> we already have checking mechanisms for this (see
>>>> resolve_fl_variable), but apparently they are not working.
>>>>
>>>> My current suspicion is that 'gfc_is_constant_expr' has a bug, because
>>>> it claims the call to the function 'get_i' to be a constant
>>>> expression. This is not true, because get_i() can not be reduced to a
>>>> compile-time constant.
>>>
>>> some more reading in the standard confirms this suspicion: In
>>> gfc_is_constant_expr there is a piece of code which claims that
>>> specification functions are constant. That is certainly not true, and
>>> so what I'm doing in the attached fix is to remove that code and add
>>> some references to the standard to make things clearer.
>>>
>>> The code that I'm removing has last been touched in this commit by
>>> Jerry six years ago:
>>>
>>> https://gcc.gnu.org/viewcvs/gcc?view=revision&revision=166520
>>>
>>> However, this did not introduce the bug in the first place (not sure
>>> when that happened).
>>>
>>> In any case the new patch in the attachment regtests cleanly and
>>> correctly rejects the original test case as well as one of the cases
>>> mentioned by Dominique. Ok for trunk?
>>>
>>> Cheers,
>>> Janus
>>>
>>>
>>>
>>> 2016-11-19  Janus Weil  <janus@gcc.gnu.org>
>>>
>>>     PR fortran/78392
>>>     * expr.c (gfc_is_constant_expr): Specification functions are not
>>>     compile-time constants. Update documentation (add reference to F08
>>>     standard), add a FIXME.
>>>     (external_spec_function): Add reference to F08 standard.
>>>     * resolve.c (resolve_fl_variable): Ditto.
>>>
>>> 2016-11-19  Janus Weil  <janus@gcc.gnu.org>
>>>
>>>     PR fortran/78392
>>>     * gfortran.dg/constant_shape.f90: New test case.