[gcc r13-5743] Fortran: error handling of global entity appearing in COMMON block [PR103259]

[Harald Anlauf <anlauf@gcc.gnu.org>]

https://gcc.gnu.org/g:7e9f20f5517429cfaadec14d6b04705e59078565

commit r13-5743-g7e9f20f5517429cfaadec14d6b04705e59078565
Author: Steve Kargl <kargl@gcc.gnu.org>
Date:   Tue Feb 7 20:18:42 2023 +0100

    Fortran: error handling of global entity appearing in COMMON block [PR103259]
    
    gcc/fortran/ChangeLog:
    
            PR fortran/103259
            * resolve.cc (resolve_common_vars): Avoid NULL pointer dereference
            when a symbol's location is not set.
    
    gcc/testsuite/ChangeLog:
    
            PR fortran/103259
            * gfortran.dg/pr103259.f90: New test.

Diff:
---
 gcc/fortran/resolve.cc                 | 12 +++++++++---
 gcc/testsuite/gfortran.dg/pr103259.f90 | 11 +++++++++++
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/gcc/fortran/resolve.cc b/gcc/fortran/resolve.cc
index 100b2382e22..549916c2b53 100644
--- a/gcc/fortran/resolve.cc
+++ b/gcc/fortran/resolve.cc
@@ -953,9 +953,15 @@ resolve_common_vars (gfc_common_head *common_block, bool named_common)
     {
       gsym = gfc_find_gsymbol (gfc_gsym_root, csym->name);
       if (gsym && (gsym->type == GSYM_MODULE || gsym->type == GSYM_PROGRAM))
-	gfc_error_now ("Global entity %qs at %L cannot appear in a "
-			"COMMON block at %L", gsym->name,
-			&gsym->where, &csym->common_block->where);
+	{
+	  if (csym->common_block)
+	    gfc_error_now ("Global entity %qs at %L cannot appear in a "
+			   "COMMON block at %L", gsym->name,
+			   &gsym->where, &csym->common_block->where);
+	  else
+	    gfc_error_now ("Global entity %qs at %L cannot appear in a "
+			   "COMMON block", gsym->name, &gsym->where);
+	}
 
       /* gfc_add_in_common may have been called before, but the reported errors
 	 have been ignored to continue parsing.
diff --git a/gcc/testsuite/gfortran.dg/pr103259.f90 b/gcc/testsuite/gfortran.dg/pr103259.f90
new file mode 100644
index 00000000000..f78ff26180e
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/pr103259.f90
@@ -0,0 +1,11 @@
+! { dg-do compile }
+! PR fortran/103259 - ICE in resolve_common_vars
+! Contributed by G.Steinmetz
+
+module m
+  integer :: p
+  common /c/ p
+end
+program p ! { dg-error "cannot appear in a COMMON block" }
+  use m   ! { dg-error "is also the name of the current program unit" }
+end