https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69423
--- Comment #7 from Paul Thomas <pault at gcc dot gnu.org> ---
(In reply to vehre from comment #6)
> What I have learnt so far:
>
> When the gimple optimisation algorithm 'remove_unused_locals ()' in
> gcc/tree-ssa-live.c is done, it has removed the temporary for the
> _gfortran_transfer_character_write's string length. In the previous analysis
> step this (ssa-)temporary has the uid 3471 in my current fortran. That var
> occurs in two basicblocks (bb), once in <bb 5> of ssa, where it is only used
> to check whether a preallocated incoming string has the correct length. That
> whole bb can be eliminated, because it is unreachable which can be deduced
> from the propagated attributes. But in the <bb 11> it must not be eliminated
> as well. Because in both bbs the uid of the temporary is the same, I tried
> several ways to prevent this association (adding a further temporary using
> gfc_evaluate_now (), copying the tree using copy_node ()), but to no avail
> yet.
>
> Having said this my assumption is, that at both occurrences of .__result_4
> the exactly same tree is used (and not a separate copy in each place). Maybe
> this is the issue, but I am still investigating. Just thought to let you
> know whether anything of this rings a bell.
Andre,
You have gone further in the diagnosis than I have. However, I would take a
look at comment #3. There is no reason at all why gimple should treat explicit
and implicit result variables differently. I THINK that the difference must lie
in the dead wood that I left in place in trans-decl.c(gfc_get_symbol_decl).
(A few minutes later) I just removed the whole lot and this did not fix this
PR. However, unsurprisingly, it does regtest OK, which tells me that the whole
lot should go.
I still can see absolutely no difference in the generated code.
Index: /svn/trunk/gcc/fortran/trans-decl.c
===================================================================
*** /svn/trunk/gcc/fortran/trans-decl.c (revision 233015)
--- /svn/trunk/gcc/fortran/trans-decl.c (working copy)
*************** gfc_get_symbol_decl (gfc_symbol * sym)
*** 1366,1386 ****
}
}
- /* All deferred character length procedures need to retain the backend
- decl, which is a pointer to the character length in the caller's
- namespace and to declare a local character length. */
- if (!byref && sym->attr.function
- && sym->ts.type == BT_CHARACTER
- && sym->ts.deferred
- && sym->ts.u.cl->passed_length == NULL
- && sym->ts.u.cl->backend_decl
- && TREE_CODE (sym->ts.u.cl->backend_decl) == PARM_DECL)
- {
- sym->ts.u.cl->passed_length = sym->ts.u.cl->backend_decl;
- gcc_assert (POINTER_TYPE_P (TREE_TYPE (sym->ts.u.cl->passed_length)));
- sym->ts.u.cl->backend_decl = build_fold_indirect_ref
(sym->ts.u.cl->backend_decl);
- }
-
fun_or_res = byref && (sym->attr.result
|| (sym->attr.function && sym->ts.deferred));
if ((sym->attr.dummy && ! sym->attr.function) || fun_or_res)
--- 1366,1371 ----
*************** gfc_get_symbol_decl (gfc_symbol * sym)
*** 1409,1447 ****
(sym->ts.u.cl->passed_length == sym->ts.u.cl->backend_decl))
sym->ts.u.cl->backend_decl = NULL_TREE;
- if (sym->ts.deferred && byref)
- {
- /* The string length of a deferred char array is stored in the
- parameter at sym->ts.u.cl->backend_decl as a reference and
- marked as a result. Exempt this variable from generating a
- temporary for it. */
- if (sym->attr.result)
- {
- /* We need to insert a indirect ref for param decls. */
- if (sym->ts.u.cl->backend_decl
- && TREE_CODE (sym->ts.u.cl->backend_decl) == PARM_DECL)
- {
- sym->ts.u.cl->passed_length = sym->ts.u.cl->backend_decl;
- sym->ts.u.cl->backend_decl =
- build_fold_indirect_ref (sym->ts.u.cl->backend_decl);
- }
- }
- /* For all other parameters make sure, that they are copied so
- that the value and any modifications are local to the routine
- by generating a temporary variable. */
- else if (sym->attr.function
- && sym->ts.u.cl->passed_length == NULL
- && sym->ts.u.cl->backend_decl)
- {
- sym->ts.u.cl->passed_length = sym->ts.u.cl->backend_decl;
- if (POINTER_TYPE_P (TREE_TYPE (sym->ts.u.cl->passed_length)))
- sym->ts.u.cl->backend_decl
- = build_fold_indirect_ref (sym->ts.u.cl->backend_decl);
- else
- sym->ts.u.cl->backend_decl = NULL_TREE;
- }
- }
-
if (sym->ts.u.cl->backend_decl == NULL_TREE)
length = gfc_create_string_length (sym);
else
--- 1394,1399 ----
Cheers
Paul
