[e-acsl] add changelog entry for physical term equality

also: add clarifying comment to the Labels module

src/plugins/e-acsl/doc/Changelog

@@ -25,6 +25,9 @@
 Plugin E-ACSL <next-release>
 ###############################################################################
 
+-* E-ACSL       [2024-09-26] fix usage of structural equality of terms;
+                By using physical equality we ensure that structurally
+                identical terms are translated according to their context.
 -* E-ACSL       [2024-09-16] fix logic variable escaping its scope
 -* E-ACSL       [2024-09-03] handle negative integers generated by RTE
 - E-ACSL        [2024-09-03] add support for labelled logic functions in case

src/plugins/e-acsl/src/analyses/labels.ml

@@ -65,6 +65,9 @@ let at_data_for_stmts: At_data.t list ref Stmt.Hashtbl.t =
     statement [stmt]. *)
 let add_at_for_stmt data stmt =
   let stmt = get_first_inner_stmt stmt in
+  (* Note that the error field is not taken into account in At_data.equal.
+     Therefore we cannot just write:
+       At_data.Hashtbl.replace ats_tbl data data; let old_data = data in *)
   let ats_ref =
     try
       Stmt.Hashtbl.find at_data_for_stmts stmt