[gcc r16-6322] fortran: fix testsuite regression for gfortran.dg/value_9.f90 [PR123201]

[Harald Anlauf]

https://gcc.gnu.org/g:abf3f0b24c4d07649266371c0f8f9625dff58cd3

commit r16-6322-gabf3f0b24c4d07649266371c0f8f9625dff58cd3
Author: Harald Anlauf <anlauf@gmx.de>
Date:   Sun Dec 21 23:03:28 2025 +0100

    fortran: fix testsuite regression for gfortran.dg/value_9.f90 [PR123201]
    
    Commit r16-3499 introduced a regression on targets where truncation of a
    string argument passed to a CHARACTER(len=1),VALUE dummy argument missed
    the special treatment needed for passing single characters.
    
            PR fortran/123201
    
    gcc/fortran/ChangeLog:
    
            * trans-expr.cc (conv_dummy_value): Convert string of length 1 to a
            single character for passing as actual argument.

Diff:
---
 gcc/fortran/trans-expr.cc | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/gcc/fortran/trans-expr.cc b/gcc/fortran/trans-expr.cc
index b549a62880e2..20f749271535 100644
--- a/gcc/fortran/trans-expr.cc
+++ b/gcc/fortran/trans-expr.cc
@@ -6654,6 +6654,14 @@ conv_dummy_value (gfc_se * parmse, gfc_expr * e, gfc_symbol * fsym,
 						  e->value.character.string);
       parmse->string_length = build_int_cst (gfc_charlen_type_node, flen);
 
+      if (flen == 1)
+	{
+	  tree slen1 = build_int_cst (gfc_charlen_type_node, 1);
+	  gfc_conv_string_parameter (parmse);
+	  parmse->expr = gfc_string_to_single_character (slen1, parmse->expr,
+							 e->ts.kind);
+	}
+
       /* Indicate value,optional scalar dummy argument as present.  */
       if (fsym->attr.optional)
 	vec_safe_push (optionalargs, boolean_true_node);