Fortran: fix treatment of character, value, optional dummy arguments [PR107444]

Fix handling of character dummy arguments that have the optional+value
attribute.  Change name of internal symbols that carry the hidden presence
status of optional arguments to distinguish them from the internal hidden
character length.  Update documentation to clarify the gfortran ABI.

gcc/fortran/ChangeLog:

	PR fortran/107444
	* trans-decl.cc (create_function_arglist): Extend presence status
	to all intrinsic types, and change prefix of internal symbol to '.'.
	* trans-expr.cc (gfc_conv_expr_present): Align to changes in
	create_function_arglist.
	(gfc_conv_procedure_call): Fix generation of procedure arguments for
	the case of character dummy arguments with optional+value attribute.
	* trans-types.cc (gfc_get_function_type): Synchronize with changes
	to create_function_arglist.
	* doc/gfortran/naming-and-argument-passing-conventions.rst: Clarify
	the gfortran argument passing conventions with regard to OPTIONAL
	dummy arguments of intrinsic type.

gcc/testsuite/ChangeLog:

	PR fortran/107444
	* gfortran.dg/optional_absent_7.f90: Adjust regex.
	* gfortran.dg/optional_absent_8.f90: New test.

1 files changed, 5 insertions, 5 deletions

diff --git a/gcc/fortran/trans-decl.cc b/gcc/fortran/trans-decl.cc
index 94988b8..217de6b 100644
--- a/gcc/fortran/trans-decl.cc
+++ b/gcc/fortran/trans-decl.cc
@@ -2708,16 +2708,16 @@ create_function_arglist (gfc_symbol * sym)
 		type = gfc_sym_type (f->sym);
 	    }
 	}
-      /* For noncharacter scalar intrinsic types, VALUE passes the value,
+      /* For scalar intrinsic types, VALUE passes the value,
 	 hence, the optional status cannot be transferred via a NULL pointer.
 	 Thus, we will use a hidden argument in that case.  */
-      else if (f->sym->attr.optional && f->sym->attr.value
-	       && !f->sym->attr.dimension && f->sym->ts.type != BT_CLASS
-	       && !gfc_bt_struct (f->sym->ts.type))
+      if (f->sym->attr.optional && f->sym->attr.value
+	  && !f->sym->attr.dimension && f->sym->ts.type != BT_CLASS
+	  && !gfc_bt_struct (f->sym->ts.type))
 	{
           tree tmp;
           strcpy (&name[1], f->sym->name);
-          name[0] = '_';
+	  name[0] = '.';
           tmp = build_decl (input_location,
 			    PARM_DECL, get_identifier (name),
 			    boolean_type_node);