[Patch] Fortran: Fix gfc_maybe_dereference_var [PR104430]

[Tobias Burnus <tobias@codesourcery.com>]

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The problem is that inside the main program,
   y = f(z)
where the the result of z is
   type(t) :: z(size(x%a))
and 'x' is a dummy argument.

'x' looses the attr.dummy in gfc_add_interface_mapping
and this leads to an additional indirect ref in
gfc_maybe_dereference_var - but after the first indirect
ref, TREE_TYPE is alread a RECORD_TYPE ...

The simple fix is to simply punt when the argument
is not a pointer or reference.

This patch additionally fixes a comment in
conv_parent_component_references.

Those parts are obvious. The only potentially risky
change is the comparison change from a name-wise comparison
to a pointer-based comparison. I think it is fine and the
testsuite did not find any issue, but you prefer, I can
also exclude it.

OK for mainline? How about GCC 10/11 backports?
(I think leaving out the last change, it should be very safe to do.)

Tobias
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Fortran: Fix gfc_maybe_dereference_var [PR104430]

	PR fortran/104430

gcc/fortran/ChangeLog:

	* trans-expr.cc (conv_parent_component_references): Fix comment;
	simplify comparison.
	(gfc_maybe_dereference_var): Avoid derefereing a nonpointer

gcc/testsuite/ChangeLog:

	* gfortran.dg/class_result_10.f90: New test.

 gcc/fortran/trans-expr.cc                     |  6 ++++--
 gcc/testsuite/gfortran.dg/class_result_10.f90 | 25 +++++++++++++++++++++++++
 2 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/gcc/fortran/trans-expr.cc b/gcc/fortran/trans-expr.cc
index eb6a78c3a62..e441952818b 100644
--- a/gcc/fortran/trans-expr.cc
+++ b/gcc/fortran/trans-expr.cc
@@ -2805,9 +2805,9 @@ conv_parent_component_references (gfc_se * se, gfc_ref * ref)
   dt = ref->u.c.sym;
   c = ref->u.c.component;
 
-  /* Return if the component is in the parent type.  */
+  /* Return if the component is in this type, i.e. not in the parent type.  */
   for (cmp = dt->components; cmp; cmp = cmp->next)
-    if (strcmp (c->name, cmp->name) == 0)
+    if (c == cmp)
       return;
 
   /* Build a gfc_ref to recursively call gfc_conv_component_ref.  */
@@ -2867,6 +2867,8 @@ tree
 gfc_maybe_dereference_var (gfc_symbol *sym, tree var, bool descriptor_only_p,
 			   bool is_classarray)
 {
+  if (!POINTER_TYPE_P (TREE_TYPE (var)))
+    return var;
   if (is_CFI_desc (sym, NULL))
     return build_fold_indirect_ref_loc (input_location, var);
 
diff --git a/gcc/testsuite/gfortran.dg/class_result_10.f90 b/gcc/testsuite/gfortran.dg/class_result_10.f90
new file mode 100644
index 00000000000..acd9a73ebda
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/class_result_10.f90
@@ -0,0 +1,25 @@
+! { dg-do run}
+!
+! PR fortran/104430
+!
+! Contributed by  G. Steinmetz 
+
+module m
+   type t
+      integer :: a
+   end type
+contains
+   function f(x) result(z)
+      class(t) :: x(:)
+      type(t) :: z(size(x%a))
+      z%a = 42
+   end
+end
+program p
+   use m
+   class(t), allocatable :: y(:), z(:)
+   allocate (y(32))
+   z = f(y)
+   if (size(z) /= 32) stop 1
+   if (any (z%a /= 42)) stop 2
+end