Hi PA, hello all,

First, I hesitate to review/approve a patch I am involved in; Thus, I would like
if someone could have a second look.

Regarding the patch itself:


On 20.10.23 16:02, Paul-Antoine Arraswrote:
> Hi all,
>
> The attached patch fixes a bug that causes valid OpenMP declare
> variant directive
> and functions to be rejected with the following error (see testcase):
>
> [...]
> Error: variant ‘foo_variant’ and base ‘foo’ at (1) have incompatible
> types: Type mismatch in argument 'c_bv' (INTEGER(8)/TYPE(c_ptr))
>
> The fix consists in special-casing this situation in gfc_compare_types().
> OK for mainline?
...
> Subject: [PATCH] Fortran: Fix incompatible types between INTEGER(8) and
>   TYPE(c_ptr)
>
> In the context of an OpenMP declare variant directive, arguments of type C_PTR
> are sometimes recognised as C_PTR in the base function and as INTEGER(8) in the
> variant - or the other way around, depending on the parsing order.
> This patch prevents such situation from turning into a compile error.
>
> 2023-10-20  Paul-Antoine Arras<pa@codesourcery.com>
>           Tobias Burnus<tobias@codesourcery.com>
>
> gcc/fortran/ChangeLog:
>
>       * interface.cc (gfc_compare_types): Return true in this situation.

That's a bad description. It makes sense when reading the commit log but if you
only read gcc/fortran/ChangeLog, 'this situation' is a dangling reference.

>   gcc/fortran/ChangeLog.omp                    |  5 ++
>   gcc/testsuite/ChangeLog.omp                  |  4 ++

On mainline, the ChangeLog not ChangeLog.omp is used. This changelog is automatically
filled by the data in the commit log. Thus, no need to include it in the patch.
(Besides: It keeps getting outdated by any other commit to that file.)

As you have a commit, running the following, possibly with the commit hash as
argument (unless it is the last commit) will show that the nightly script will use:

./contrib/gcc-changelog/git_check_commit.py -v -p

It is additionally a good check whether you got the syntax right. (This is run
as pre-commit hook.)

* * *

Regarding the patch, I think it will work, but I wonder whether we can do
better - esp. regarding c_ptr vs. c_funptr.

I started by looking why the current code fails:

> index e9843e9549c..8bd35fd6d22 100644
> --- a/gcc/fortran/interface.cc
> +++ b/gcc/fortran/interface.cc
> @@ -705,12 +705,17 @@ gfc_compare_types (gfc_typespec *ts1, gfc_typespec *ts2)
> -
> -  if (((ts1->type == BT_INTEGER && ts2->type == BT_DERIVED)
> -       || (ts1->type == BT_DERIVED && ts2->type == BT_INTEGER))
> -      && ts1->u.derived && ts2->u.derived
> -      && ts1->u.derived == ts2->u.derived)

This does not work because the pointers to the derived type are different:

(gdb) p *ts1
$10 = {type = BT_INTEGER, kind = 8, u = {derived = 0x30c66b0, cl = 0x30c66b0, pad = 51144368}, interface = 0x0, is_c_interop = 1, is_iso_c = 0, f90_type = BT_VOID, deferred = false,
   interop_kind = 0x0}

(gdb) p *ts2
$11 = {type = BT_DERIVED, kind = 0, u = {derived = 0x30c2930, cl = 0x30c2930, pad = 51128624}, interface = 0x0, is_c_interop = 0, is_iso_c = 0, f90_type = BT_UNKNOWN,
   deferred = false, interop_kind = 0x0}

The reason seems to be that they are freshly created
in different namespaces. Consequently, attr.use_assoc = 1
and the namespace is different, i.e.


(gdb) p ts1->u.derived->ns->proc_name->name
$18 = 0x7ffff6ff4138 "foo"

(gdb) p ts2->u.derived->ns->proc_name->name
$19 = 0x7ffff6ffc260 "foo_variant"

* * *

Having said this, I think we can combine the current
and the modified version, i.e.

> +  if ((ts1->type == BT_INTEGER && ts2->type == BT_DERIVED
> +       && ts1->f90_type == BT_VOID
> +       && ts2->u.derived->ts.is_iso_c
> +       && ts2->u.derived->ts.u.derived->ts.f90_type == BT_VOID)
> +      || (ts2->type == BT_INTEGER && ts1->type == BT_DERIVED
> +       && ts2->f90_type == BT_VOID
> +       && ts1->u.derived->ts.is_iso_c
> +       && ts1->u.derived->ts.u.derived->ts.f90_type == BT_VOID))

See attached patch for a combined version, which checks now
whether from_intmod == INTMOD_ISO_C_BINDING and then compares
the names (to distinguish c_ptr and c_funptr). Those are unaffected
by 'use' renames, hence, we should be fine.

While in this example, the name pointers are identical, I fear that
won't hold in some more complex indirect use via module-use. Thus,
strcmp is used.

(gdb) p ts1->u.derived->name
$13 = 0x7ffff6ff4100 "c_ptr"

(gdb) p ts2->u.derived->name
$14 = 0x7ffff6ff4100 "c_ptr"

* * *

Additionally, I think it would be good to have a testcase which checks for
   c_funptr vs. c_ptr
mismatch.

Just changing c_ptr to c_funptr in the testcase (+ commenting the c_f_pointer)
prints:
   Error: variant ‘foo_variant’ and base ‘foo’ at (1) have incompatible types: Type mismatch in argument 'c_bv' (INTEGER(8)/TYPE(c_funptr))

I think that would be a good invalid testcase besides the valid one.

But with a tweak to get better messages to give:
   Error: variant ‘foo_variant’ and base ‘foo’ at (1) have incompatible types: Type mismatch in argument 'c_bv' (TYPE(c_ptr)/TYPE(c_funptr))

cf. misc.cc in the attached proposal for the *.cc files, only.

Tobias
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