Re: [PATCH] PR fortran/91300 - runtime error message with allocate and errmsg=

[Tobias Burnus <tobias@codesourcery.com>]

On 28.05.22 22:25, Harald Anlauf via Fortran wrote:
> the PR rightfully complained that we did not differentiate errors on
> ALLOCATE(...,stat=,errmsg=) for failures from allocation of already
> allocated objects or insufficient virtual memory.
It is even worse: The error message states the wrong reason.
> The attached patch introduces a new STAT value LIBERROR_NO_MEMORY
> that is returned for insufficient virtual memory, and a corresponding
> (simple and invariant) ERRMSG: "Insufficient virtual memory".
I think the message is fine – at least on Linux 'virtual memory' is
what's used and it is clear what's meant, even if I stumble a bit about
the wording. (But do not have a crisp short & comprehensive wording myself.)
> (In the PR Janne mentions checking for errno, but since the standard
> malloc(3) only mentions ENOMEM as possible error value, and the user
> may replace malloc by a special library, I believe that won't be easy
> to handle in a general way.)
I con concur. Especially as POSIX and the Linux manpage only list ENOMEM
as only value.
> Most compilers I tried (Intel/NAG/Crayftn) behave similarly, except
> for Nvidia/Flang, which try to return the size of the allocation in
> the error message.
>
> I am not sure that this is worth the effort.
I think it is not needed – especially as we generate the message in the
FE and not in libgfortran. The advantage for the users is that they know
what value has been requested – but they cannot really do much with the
knowledge, either.
> The testcase should be able to handle 32 and 64 bit systems.
> At least that's what I think.

I hope it is – at least on 64bit, I currently expect it too fail
somewhat reliably, with 32bit I think it won't – but that's also handled.

But you could add a -fdump-tree-original + '! { dg-final {
scan-tree-dump*' to do some checking in addition (e.g. whether both
strings appear in the dump; could be more complex, but that's probably
not needed).

> Regtested on x86_64-pc-linux-gnu.  OK for mainline?  Suggestions?

LGTM – with considering comments on the testcase.


> Fortran: improve runtime error message with ALLOCATE and ERRMSG=

Consider appending [PR91300] in that line – and try to make the
gcc-patches@ and fortran@ lines the same

(Searching for the PR number or case-insignificantly for the string in
the mailing list archive, will fine the message; thus, that's okay.)

> ALLOCATE: generate different STAT,ERRMSG results for failures from
> allocation of already allocated objects or insufficient virtual memory.
>
> gcc/fortran/ChangeLog:
>
>       PR fortran/91300
>       * libgfortran.h: Define new error code LIBERROR_NO_MEMORY.
>       * trans-stmt.cc (gfc_trans_allocate): Generate code for setting
>       ERRMSG depending on result of STAT result of ALLOCATE.
>       * trans.cc (gfc_allocate_using_malloc): Use STAT value of
>       LIBERROR_NO_MEMORY in case of failed malloc.
>
> gcc/testsuite/ChangeLog:
>
>       PR fortran/91300
>       * gfortran.dg/allocate_alloc_opt_15.f90: New test.
> ---
...

> +  stat1   = -1
> +  errmsg1 = ""
> +  allocate (array(1), stat=stat1, errmsg=errmsg1)
> +  if (stat1   /=  0) stop 1
> +  if (errmsg1 /= "") stop 1
Consider to init the errmsg1 and then check that is has not been
touched. (For completeness, I think we already have such tests).
> +  ! Obtain stat,errmsg for attempt to allocate an allocated object
> +  allocate (array(1), stat=stat1, errmsg=errmsg1)
> +  if (stat1   ==  0) stop 2
> +  if (errmsg1 == "") stop 2
Consider to check (either here or as a third test) for the
gfortran-specific error message.
> +  stat2   = -1
> +  errmsg2 = ""
> +  ! Try to allocate very large object
> +  allocate (bigarray(bignumber), stat=stat2, errmsg=errmsg2)
> +  if (stat2 /= 0) then
> +     print *, "stat  =", stat1
> +     print *, "errmsg: ", trim (errmsg1)
> +     print *, "stat  =", stat2
> +     print *, "errmsg: ", trim (errmsg2)
> +     ! Ensure different results for stat, errmsg variables
> +     if (stat2   == stat1                     ) stop 3
> +     if (errmsg2 == "" .or. errmsg2 == errmsg1) stop 4

Likewise for errmsg2

Thanks,

Tobias

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