Re: [PATCH] openmp, fortran: Fix ICE when the procedure name cannot be found in declare variant directives [PR104428]

[Tobias Burnus]

Kwok Cheung Yeung wrote:
This patch fixes an ICE due to a null-pointer dereference when finding 
the symbol for the procedure name in a declare variant directive, 
which occurs because the result of gfc_find_sym_tree is being 
dereferenced unconditionally. The result is now checked, and the 
symbol is set to NULL if it can't be found, resulting in a subsequent 
error.

If the symbol is implicitly typed, then the error will also occur. I 
think this makes sense as implicit variables are of type integer or 
real, which cannot be used to specify the variant procedure.

The latter sounds wrong – but fortunately, there seems to be no issue, if I 
look at:

program p
  interface
    function x()
    end function x
  end interface
  print *, foo()
  !$omp do
  do i = 1, 1
    print *, foo()
  end do
contains
  function foo()
    !$omp declare variant(x) match(construct={do})
  end
end

which compiles just fine. (The functions should be implicitly real.)

Tested on x86_64 host, okay for trunk?

LGTM, including backporting. (At least backporting to GCC 15 seems to 
make sense; it is marked as [13/14/15/16 Regression], but was reported 
against GCC 12 in Feb 2022.)

Minor comments:

gcc/fortran/

        PR fortran/104428
        * trans-openmp.cc (gfc_trans_omp_declare_variant): Check that proc_st
        is non-NULL before dereferencing.  Add line number to error message.

Thanks for using the location data for the error message!


--- a/gcc/fortran/trans-openmp.cc
…
-         variant_proc_sym = proc_st->n.sym;
+         variant_proc_sym = proc_st ? proc_st->n.sym : NULL;
        }
        if (variant_proc_sym == NULL)
        {
-         gfc_error ("Cannot find symbol %qs", variant_proc_name);
+         gfc_error ("Cannot find symbol %qs at %L", variant_proc_name,
+

--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/gomp/pr104428.f90
@@ -0,0 +1,16 @@
+! { dg-do compile }
+! { dg-options "-fopenmp" }

This shouldn't be needed for gomp/

…

+    !$omp declare variant(y) match(construct={do}) ! { dg-error "Cannot find symbol 
.y." }

GCC is run such that 'y' works – i.e. not printing some fancy quotation 
marks like ‘…’ or “…” or «…» (and contrary to "(1)", also no \\ escaping 
is required).

Thanks for the patch!

Tobias