Dear All, This bug took a silly amount of effort to diagnose but once done, the fix was obvious.
The bug is triggered in this function from the reporter's source file gfc_graph.F90: function GraphIterAppendVertex(this,vertex) result(ierr) !Appends a new vertex to the graph. implicit none integer(INTD):: ierr !out: error code class(graph_iter_t), intent(inout):: this !inout: graph iterator class(graph_vertex_t), intent(in), target:: vertex !in: new vertex type(vert_link_refs_t):: vlr ierr=this%vert_it%append(vertex) !<===== right here! ....snip.... return end function GraphIterAppendVertex 'vertex' is being passed to a class(*) dummy. As you will see from the attached patch and the ChangeLog, 'vertex' was being cast as unlimited polymorphic and assigned to the passed actual argument. This left the _len field indeterminate since it is not present in normal (limited?) polymorphic objects. Further down the way, in stsubs.F90(clone_object) an allocation is being made using the unlimited version of 'vertex as a source. Since the size passed to malloc for an unlimited source is, for _len > 0, the value of the _len multiplied by the vtable _size, the amount of memory is also indeterminate and causes the operating system to flag a failed allocation, pretty much at random. The ChangeLog and the patch describe the fix sufficiently well as not to require further explanation. I will write a testcase that tests the tree dump for the _len field before committing the patch. Bootstraps and regtests on FC23/x86_64 - OK for 7- and 8-branches? If I do not receive any contrary comments, I will commit tonight. Regards Paul 2017-10-30 Paul Thomas <pa...@gcc.gnu.org> PR fortran/80850 * trans_expr.c (gfc_conv_procedure_call): When passing a class argument to an unlimited polymorphic dummy, it is wrong to cast the passed expression as unlimited, unless it is unlimited. The correct way is to assign to each of the fields and set the _len field to zero.
Index: gcc/fortran/trans-expr.c =================================================================== *** gcc/fortran/trans-expr.c (revision 254196) --- gcc/fortran/trans-expr.c (working copy) *************** gfc_conv_procedure_call (gfc_se * se, gf *** 5173,5182 **** } else { ! gfc_add_modify (&parmse.pre, var, ! fold_build1_loc (input_location, ! VIEW_CONVERT_EXPR, ! type, parmse.expr)); parmse.expr = gfc_build_addr_expr (NULL_TREE, var); } } --- 5173,5198 ---- } else { ! if (!UNLIMITED_POLY (e) && UNLIMITED_POLY (fsym)) ! { ! tmp = gfc_class_data_get (var); ! gfc_add_modify (&parmse.pre, tmp, ! gfc_class_data_get (parmse.expr)); ! tmp = gfc_class_vptr_get (var); ! gfc_add_modify (&parmse.pre, tmp, ! gfc_class_vptr_get (parmse.expr)); ! tmp = gfc_class_len_get (var); ! gfc_add_modify (&parmse.pre, tmp, ! build_int_cst (TREE_TYPE (tmp), 0)); ! } ! else ! { ! tmp = fold_build1_loc (input_location, ! VIEW_CONVERT_EXPR, ! type, parmse.expr); ! gfc_add_modify (&parmse.pre, var, tmp); ! ; ! } parmse.expr = gfc_build_addr_expr (NULL_TREE, var); } }