[Bug fortran/43990] [OOP] ICE in output_constructor_regular_field, at varasm.c:4995

[burnus at gcc dot gnu dot org]

------- Comment #2 from burnus at gcc dot gnu dot org  2010-05-05 14:12 -------
The problem seems to be the initialization at gfc_conv_structure (init = 1) in
trans-expr.c:

We have:
     logical :: l = .true.
     class(t),pointer :: cp => null()
and thus:

(gdb) p expr->ts.u.derived->components->name
$12 = 0x2aaaaab41ea8 "l"
(gdb) p expr->ts.u.derived->components->next->name
$13 = 0x2aaaaab41eb8 "cp"
(gdb) p expr->ts.u.derived->components->next->ts.type
$14 = BT_CLASS
(gdb) p expr->ts.u.derived->components->next->attr.pointer
$15 = 0

The later is simply not true: We have a pointer.

      if (cm->ts.type == BT_CLASS && !cm->attr.proc_pointer)
        {
          gfc_component *data;
          data = gfc_find_component (cm->ts.u.derived, "$data", true, true);

Somehow this gives the wrong result in terms of the offset, i.e. one tries to
initialize:

t.l at position (&t + (0 byte)) and then one tries to initialize t.$data (!) at
(&t + 0)  but it should be (&t + 4) - or (&(t.class) + 0).

The following patch fixes the problem, though I have the feeling it papers over
some logic problem (cf. below):

--- a/gcc/fortran/trans-expr.c
+++ b/gcc/fortran/trans-expr.c
@@ -4328,10 +4328,9 @@ gfc_conv_structure (gfc_se * se, gfc_expr * expr, int
init)
        c; c = gfc_constructor_next (c), cm = cm->next)
     {
       /* Skip absent members in default initializers and allocatable
-        components.  Although the latter have a default initializer
-        of EXPR_NULL,... by default, the static nullify is not needed
-        since this is done every time we come into scope.  */
-      if (!c->expr || cm->attr.allocatable)
+        components, and NULL initialization of pointers, which are
+        automatically handled through zero initialization.  */
+      if (!c->expr || cm->attr.allocatable || c->expr->expr_type == EXPR_NULL)
         continue;

       if (cm->ts.type == BT_CLASS && !cm->attr.proc_pointer)

(By the way, the comment above looked bogus: "since this is done every time we
come in scope" is only true if the variable is STATIC just due to
-fmax-stack-var-size. Otherwise, it will be ("only") zero initialized through
"= {}".)

 * * *

The "fix" above is likely to break if one uses
  <type>, pointer :: ptr => nonNULLtarget
(allowed since Fortran 2008) where the RHS can be something different than
EXPR_NULL. The problem seems to be that already the class struct is a pointer
and not only its content, i.e. "t.class.$data = NULL" vs. "t.class == NULL". Or
maybe only the reference goes wrong; cf. t.class.$data (OK) vs. t.$data
(wrong).


F2008 has:

R442 component-initialization is = constant-expr
                              or => null-init
                              or => initial-data-target
R443 initial-data-target is designator
C461 (R443) The designator shall designate a nonallocatable variable that has
the TARGET and SAVE attributes and does not have a vector subscript. Every
subscript, section subscript, substring starting point, and substring ending
point in designator shall be a constant expression."

 * * *

Failing dump (for PROGRAM - not shown for MODULE):
  static struct t default_t = {.l=1, .$data=0B};
working with the patch above:
  static struct t default_t = {.l=1};


-- 

burnus at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pault at gcc dot gnu dot org
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2010-05-05 14:12:54
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43990