Generalize predicates from unary to nary

Summary:
Add support for nary predicates, not just unary ones.  Many operations
don't make much sense for nullary predicates, and are generally treated
as no-ops.  The first argument is treated specially, as the "anchor" of
the predicate application.  For example, adding or removing an attribute
uses the anchor to identify the atom to operate on.  Also, abstraction
and normalization operations treat the anchor specially.

Reviewed By: cristianoc

Differential Revision: D3669391

fbshipit-source-id: 3d142ea

infer/src/IR/Cfg.re

@@ -962,8 +962,8 @@ let remove_abducted_retvars p =>
             fun
             | Sil.Aeq lhs rhs
             | Sil.Aneq lhs rhs => exp_contains lhs || exp_contains rhs
-            | Sil.Apred _ e
-            | Sil.Anpred _ e => exp_contains e
+            | Sil.Apred _ es
+            | Sil.Anpred _ es => IList.exists exp_contains es
           )
           pi
       };

infer/src/IR/Sil.re

@@ -85,7 +85,14 @@ type res_action = {
 };
 
 
-/** Attributes */
+/** Attributes are nary function symbols that are applied to expression arguments in Apred and
+    Anpred atomic formulas.  Many operations don't make much sense for nullary predicates, and are
+    generally treated as no-ops.  The first argument is treated specially, as the "anchor" of the
+    predicate application.  For example, adding or removing an attribute uses the anchor to identify
+    the atom to operate on.  Also, abstraction and normalization operations treat the anchor
+    specially and maintain more information on it than other arguments.  Therefore when attaching an
+    attribute to an expression, that expression should be the first argument, optionally followed by
+    additional related expressions. */
 type attribute =
   | Aresource of res_action /** resource acquire/release */
   | Aautorelease
@@ -203,8 +210,8 @@ type offset = | Off_fld of Ident.fieldname Typ.t | Off_index of exp;
 type atom =
   | Aeq of exp exp /** equality */
   | Aneq of exp exp /** disequality */
-  | Apred of attribute exp /** predicate symbol applied to an exp */
-  | Anpred of attribute exp /** negated predicate symbol applied to an exp */;
+  | Apred of attribute (list exp) /** predicate symbol applied to exps */
+  | Anpred of attribute (list exp) /** negated predicate symbol applied to exps */;
 
 
 /** kind of lseg or dllseg predicates */
@@ -705,21 +712,21 @@ let atom_compare a b =>
       }
     | (Aneq _, _) => (-1)
     | (_, Aneq _) => 1
-    | (Apred a1 e1, Apred a2 e2) =>
+    | (Apred a1 es1, Apred a2 es2) =>
       let n = attribute_compare a1 a2;
       if (n != 0) {
         n
       } else {
-        exp_compare e1 e2
+        IList.compare exp_compare es1 es2
       }
     | (Apred _, _) => (-1)
     | (_, Apred _) => 1
-    | (Anpred a1 e1, Anpred a2 e2) =>
+    | (Anpred a1 es1, Anpred a2 es2) =>
       let n = attribute_compare a1 a2;
       if (n != 0) {
         n
       } else {
-        exp_compare e1 e2
+        IList.compare exp_compare es1 es2
       }
     }
   };
@@ -1286,8 +1293,8 @@ let pp_atom pe0 f a => {
     | PP_HTML => F.fprintf f "%a != %a" (pp_exp pe) e1 (pp_exp pe) e2
     | PP_LATEX => F.fprintf f "%a{\\neq}%a" (pp_exp pe) e1 (pp_exp pe) e2
     }
-  | Apred a e => F.fprintf f "%s(%a)" (attribute_to_string pe a) (pp_exp pe) e
-  | Anpred a e => F.fprintf f "!%s(%a)" (attribute_to_string pe a) (pp_exp pe) e
+  | Apred a es => F.fprintf f "%s(%a)" (attribute_to_string pe a) (pp_comma_seq (pp_exp pe)) es
+  | Anpred a es => F.fprintf f "!%s(%a)" (attribute_to_string pe a) (pp_comma_seq (pp_exp pe)) es
   };
   color_post_wrapper changed pe0 f
 };
@@ -1942,8 +1949,8 @@ let atom_expmap (f: exp => exp) =>
   fun
   | Aeq e1 e2 => Aeq (f e1) (f e2)
   | Aneq e1 e2 => Aneq (f e1) (f e2)
-  | Apred a e => Apred a (f e)
-  | Anpred a e => Anpred a (f e);
+  | Apred a es => Apred a (IList.map f es)
+  | Anpred a es => Anpred a (IList.map f es);
 
 let atom_list_expmap (f: exp => exp) (alist: list atom) => IList.map (atom_expmap f) alist;
 
@@ -2080,8 +2087,8 @@ let atom_fpv =
   fun
   | Aeq e1 e2 => exp_fpv e1 @ exp_fpv e2
   | Aneq e1 e2 => exp_fpv e1 @ exp_fpv e2
-  | Apred _ e
-  | Anpred _ e => exp_fpv e;
+  | Apred _ es
+  | Anpred _ es => IList.fold_left (fun fpv e => IList.rev_append (exp_fpv e) fpv) [] es;
 
 let rec strexp_fpv =
   fun
@@ -2292,8 +2299,8 @@ let atom_fav_add fav =>
       exp_fav_add fav e1;
       exp_fav_add fav e2
     }
-  | Apred _ e
-  | Anpred _ e => exp_fav_add fav e;
+  | Apred _ es
+  | Anpred _ es => IList.iter (fun e => exp_fav_add fav e) es;
 
 let atom_fav = fav_imperative_to_functional atom_fav_add;
 

infer/src/IR/Sil.rei

@@ -73,7 +73,14 @@ type res_action = {
 };
 
 
-/** Attributes */
+/** Attributes are nary function symbols that are applied to expression arguments in Apred and
+    Anpred atomic formulas.  Many operations don't make much sense for nullary predicates, and are
+    generally treated as no-ops.  The first argument is treated specially, as the "anchor" of the
+    predicate application.  For example, adding or removing an attribute uses the anchor to identify
+    the atom to operate on.  Also, abstraction and normalization operations treat the anchor
+    specially and maintain more information on it than other arguments.  Therefore when attaching an
+    attribute to an expression, that expression should be the first argument, optionally followed by
+    additional related expressions. */
 type attribute =
   | Aresource of res_action /** resource acquire/release */
   | Aautorelease
@@ -197,8 +204,8 @@ type offset = | Off_fld of Ident.fieldname Typ.t | Off_index of exp;
 type atom =
   | Aeq of exp exp /** equality */
   | Aneq of exp exp /** disequality */
-  | Apred of attribute exp /** predicate symbol applied to an exp */
-  | Anpred of attribute exp /** negated predicate symbol applied to an exp */;
+  | Apred of attribute (list exp) /** predicate symbol applied to exps */
+  | Anpred of attribute (list exp) /** negated predicate symbol applied to exps */;
 
 
 /** kind of lseg or dllseg predicates */

infer/src/backend/abs.ml

@@ -788,7 +788,7 @@ let abstract_pure_part p ~(from_abstract_footprint: bool) =
                 | Sil.Const _ -> a :: pi
                 | _ -> pi)
            | Sil.Aneq (Var _, _)
-           | Sil.Apred (_, Var _) | Anpred (_, Var _) -> a :: pi
+           | Sil.Apred (_, Var _ :: _) | Anpred (_, Var _ :: _) -> a :: pi
            | Sil.Aeq _ | Aneq _ | Apred _ | Anpred _ -> pi
         )
         [] pi_filtered in
@@ -820,11 +820,11 @@ let abstract_gc p =
         let no_fav_e1 = Sil.fav_is_empty fav_e1 in
         let no_fav_e2 = Sil.fav_is_empty fav_e2 in
         (no_fav_e1 || intersect_e1 ()) && (no_fav_e2 || intersect_e2 ())
-    | Sil.Apred (_, e) | Anpred (_, e) ->
-        let fav_e = Sil.exp_fav e in
-        Sil.fav_is_empty fav_e
+    | (Sil.Apred _ | Anpred _) as a ->
+        let fav_a = Sil.atom_fav a in
+        Sil.fav_is_empty fav_a
         ||
-        IList.intersect Ident.compare (Sil.fav_to_list fav_e) (Sil.fav_to_list fav_p_without_pi) in
+        IList.intersect Ident.compare (Sil.fav_to_list fav_a) (Sil.fav_to_list fav_p_without_pi) in
   let new_pi = IList.filter strong_filter pi in
   let prop = Prop.normalize (Prop.replace_pi new_pi p) in
   match Prop.prop_iter_create prop with

infer/src/backend/dom.ml

@@ -718,13 +718,13 @@ end = struct
           when (exp_contains_only_normal_ids e' && not (Ident.is_normal id)) ->
             build_other_atoms (fun e0 -> Prop.mk_neq e0 e') side e
 
-        | Sil.Apred (a, (Var id as e))
-          when not (Ident.is_normal id) ->
-            build_other_atoms (fun e0 -> Prop.mk_pred a e0) side e
+        | Sil.Apred (a, (Var id as e) :: es)
+          when not (Ident.is_normal id) && IList.for_all exp_contains_only_normal_ids es ->
+            build_other_atoms (fun e0 -> Prop.mk_pred a (e0 :: es)) side e
 
-        | Sil.Anpred (a, (Var id as e))
-          when not (Ident.is_normal id) ->
-            build_other_atoms (fun e0 -> Prop.mk_npred a e0) side e
+        | Sil.Anpred (a, (Var id as e) :: es)
+          when not (Ident.is_normal id) && IList.for_all exp_contains_only_normal_ids es ->
+            build_other_atoms (fun e0 -> Prop.mk_npred a (e0 :: es)) side e
 
         | Sil.Aeq((Sil.Var id as e), e') | Sil.Aeq(e', (Sil.Var id as e))
           when (exp_contains_only_normal_ids e' && not (Ident.is_normal id)) ->
@@ -1674,8 +1674,8 @@ let pi_partial_join mode
         true
     | Sil.Aneq _ -> false
     | Sil.Aeq _ as e -> Prop.atom_is_inequality e
-    | Sil.Apred (_, e) | Anpred (_, e) ->
-        exp_is_const e in
+    | Sil.Apred (_, es) | Anpred (_, es) ->
+        IList.for_all exp_is_const es in
   begin
     if Config.trace_join then begin
       L.d_str "pi1: "; Prop.d_pi pi1; L.d_ln ();

infer/src/backend/modelBuiltins.ml

@@ -313,7 +313,7 @@ let execute___cast builtin_args
 let set_resource_attribute prop path n_lexp loc ra_res =
   let prop' = match Prop.get_resource_attribute prop n_lexp with
     | Some (Apred (Aresource ra, _)) ->
-        Prop.add_or_replace_exp_attribute prop (Apred (Aresource { ra with ra_res }, n_lexp))
+        Prop.add_or_replace_attribute prop (Apred (Aresource { ra with ra_res }, [n_lexp]))
     | _ ->
         let pname = Sil.mem_alloc_pname Sil.Mnew in
         let ra =
@@ -323,7 +323,7 @@ let set_resource_attribute prop path n_lexp loc ra_res =
             ra_pname = pname;
             ra_loc = loc;
             ra_vpath = None } in
-        Prop.add_or_replace_exp_attribute prop (Apred (Aresource ra, n_lexp)) in
+        Prop.add_or_replace_attribute prop (Apred (Aresource ra, [n_lexp])) in
   [(prop', path)]
 
 (** Set the attibute of the value as file *)
@@ -545,7 +545,7 @@ let execute___set_autorelease_attribute
       let prop = return_result lexp prop_ ret_ids in
       if Config.objc_memory_model_on then
         let n_lexp, prop = check_arith_norm_exp pname lexp prop in
-        let prop' = Prop.add_or_replace_exp_attribute prop (Apred (Aautorelease, n_lexp)) in
+        let prop' = Prop.add_or_replace_attribute prop (Apred (Aautorelease, [n_lexp])) in
         [(prop', path)]
       else execute___no_op prop path
   | _ -> raise (Exceptions.Wrong_argument_number __POS__)
@@ -555,11 +555,11 @@ let execute___release_autorelease_pool
     ({ Builtin.prop_; path; } as builtin_args)
   : Builtin.ret_typ =
   if Config.objc_memory_model_on then
-    let autoreleased_objects = Prop.get_atoms_with_attribute Sil.Aautorelease prop_ in
+    let autoreleased_objects = Prop.get_atoms_with_attribute prop_ Sil.Aautorelease in
     let prop_without_attribute = Prop.remove_attribute prop_ Aautorelease in
-    let call_release res exp =
-      match res with
-      | (prop', path'):: _ ->
+    let call_release res atom =
+      match res, atom with
+      | ((prop', path') :: _, Sil.Apred (_, exp :: _)) ->
           (try
              let hpred = IList.find (function
                  | Sil.Hpointsto(e1, _, _) -> Sil.exp_equal e1 exp
@@ -575,19 +575,19 @@ let execute___release_autorelease_pool
                  res1
              | _ -> res
            with Not_found -> res)
-      | [] -> res in
+      | _ -> res in
     IList.fold_left call_release [(prop_without_attribute, path)] autoreleased_objects
   else execute___no_op prop_ path
 
 let set_attr pdesc prop path exp attr =
   let pname = Cfg.Procdesc.get_proc_name pdesc in
   let n_lexp, prop = check_arith_norm_exp pname exp prop in
-  [(Prop.add_or_replace_exp_attribute prop (Apred (attr, n_lexp)), path)]
+  [(Prop.add_or_replace_attribute prop (Apred (attr, [n_lexp])), path)]
 
 let delete_attr pdesc prop path exp attr =
   let pname = Cfg.Procdesc.get_proc_name pdesc in
   let n_lexp, prop = check_arith_norm_exp pname exp prop in
-  [(Prop.remove_attribute_from_exp prop (Apred (attr, n_lexp)), path)]
+  [(Prop.remove_attribute_from_exp prop (Apred (attr, [n_lexp])), path)]
 
 
 (** Set attibute att *)
@@ -694,8 +694,8 @@ let _execute_free mk loc acc iter =
           Sil.ra_vpath = None } in
       (* mark value as freed *)
       let p_res =
-        Prop.add_or_replace_exp_attribute_check_changed
-          Tabulation.check_attr_dealloc_mismatch prop (Apred (Aresource ra, lexp)) in
+        Prop.add_or_replace_attribute_check_changed
+          Tabulation.check_attr_dealloc_mismatch prop (Apred (Aresource ra, [lexp])) in
       p_res :: acc
   | (Sil.Hpointsto _, _ :: _) -> assert false (* alignment error *)
   | _ -> assert false (* should not happen *)
@@ -796,7 +796,7 @@ let execute_alloc mk can_return_null
         Sil.ra_loc = loc;
         Sil.ra_vpath = None } in
     (* mark value as allocated *)
-    Prop.add_or_replace_exp_attribute prop' (Apred (Aresource ra, exp_new)) in
+    Prop.add_or_replace_attribute prop' (Apred (Aresource ra, [exp_new])) in
   let prop_alloc = Prop.conjoin_eq (Sil.Var ret_id) exp_new prop_plus_ptsto in
   if can_return_null then
     let prop_null = Prop.conjoin_eq (Sil.Var ret_id) Sil.exp_zero prop in

infer/src/backend/prop.ml

@@ -1034,10 +1034,10 @@ let atom_normalize sub a0 =
         handle_boolean_operation true e1 e2
     | Sil.Aneq (e1, e2) ->
         handle_boolean_operation false e1 e2
-    | Sil.Apred (a, e) ->
-        Sil.Apred (a, exp_normalize sub e)
-    | Sil.Anpred (a, e) ->
-        Sil.Anpred (a, exp_normalize sub e) in
+    | Sil.Apred (a, es) ->
+        Sil.Apred (a, IList.map (fun e -> exp_normalize sub e) es)
+    | Sil.Anpred (a, es) ->
+        Sil.Anpred (a, IList.map (fun e -> exp_normalize sub e) es) in
   if atom_is_inequality a' then inequality_normalize a' else a'
 
 (** Negate an atom *)
@@ -1048,8 +1048,8 @@ let atom_negate = function
       mk_inequality (Sil.exp_le e2 e1)
   | Sil.Aeq (e1, e2) -> Sil.Aneq (e1, e2)
   | Sil.Aneq (e1, e2) -> Sil.Aeq (e1, e2)
-  | Sil.Apred (a, e) -> Sil.Anpred (a, e)
-  | Sil.Anpred (a, e) -> Sil.Apred (a, e)
+  | Sil.Apred (a, es) -> Sil.Anpred (a, es)
+  | Sil.Anpred (a, es) -> Sil.Apred (a, es)
 
 let rec strexp_normalize sub se =
   match se with
@@ -1475,10 +1475,10 @@ let mk_neq e1 e2 = mk_atom (Aneq (e1, e2))
 let mk_eq e1 e2 = mk_atom (Aeq (e1, e2))
 
 (** Construct a pred. *)
-let mk_pred a e = mk_atom (Apred (a, e))
+let mk_pred a es = mk_atom (Apred (a, es))
 
 (** Construct a negated pred. *)
-let mk_npred a e = mk_atom (Anpred (a, e))
+let mk_npred a es = mk_atom (Anpred (a, es))
 
 (** Construct a points-to predicate for a single program variable.
     If [expand_structs] is true, initialize the fields of structs with fresh variables. *)
@@ -1613,7 +1613,7 @@ let compute_reachable_atoms pi exps =
   IList.filter
     (function
       | Sil.Aeq (lhs, rhs) | Aneq (lhs, rhs) -> exp_contains lhs || exp_contains rhs
-      | Sil.Apred (_, e) | Anpred (_, e) -> exp_contains e)
+      | Sil.Apred (_, es) | Anpred (_, es) -> IList.exists exp_contains es)
     pi
 
 (** Eliminates all empty lsegs from sigma, and collect equalities
@@ -1776,21 +1776,21 @@ let prop_reset_inst inst_map prop =
 (** {2 Attributes} *)
 
 (** Return the exp and attribute marked in the atom if any, and return None otherwise *)
-let atom_get_exp_attribute atom =
+let atom_get_attribute atom =
   match atom with
   | Sil.Apred _ | Anpred _ -> Some atom
   | _ -> None
 
 (** Check whether an atom is used to mark an attribute *)
 let atom_is_attribute a =
-  atom_get_exp_attribute a <> None
+  atom_get_attribute a <> None
 
 (** Get the attribute associated to the expression, if any *)
-let get_exp_attributes prop exp =
+let get_attributes prop exp =
   let nexp = exp_normalize_prop prop exp in
   let atom_get_attr attributes atom =
     match atom with
-    | Sil.Apred (_, e) | Anpred (_, e) when Sil.exp_equal e nexp -> atom :: attributes
+    | Sil.Apred (_, es) | Anpred (_, es) when IList.mem Sil.exp_equal nexp es -> atom :: attributes
     | _ -> attributes in
   IList.fold_left atom_get_attr [] prop.pi
 
@@ -1800,7 +1800,7 @@ let attributes_in_same_category attr1 attr2 =
   Sil.attribute_category_equal cat1 cat2
 
 let get_attribute prop exp category =
-  let atts = get_exp_attributes prop exp in
+  let atts = get_attributes prop exp in
   try
     Some
       (IList.find (function
@@ -1835,7 +1835,7 @@ let get_retval_attribute prop exp =
   get_attribute prop exp Sil.ACretval
 
 let has_dangling_uninit_attribute prop exp =
-  let la = get_exp_attributes prop exp in
+  let la = get_attributes prop exp in
   IList.exists (function
       | Sil.Apred (a, _) -> Sil.attribute_equal a (Adangling DAuninit)
       | _ -> false
@@ -1844,49 +1844,50 @@ let has_dangling_uninit_attribute prop exp =
 (** Get all the attributes of the prop *)
 let get_all_attributes prop =
   let res = ref [] in
-  let do_atom a = match atom_get_exp_attribute a with
+  let do_atom a = match atom_get_attribute a with
     | Some attr -> res := attr :: !res
     | None -> () in
   IList.iter do_atom prop.pi;
   IList.rev !res
 
-(** Set an attribute associated to the expression *)
-let set_exp_attribute ?(footprint = false) ?(polarity = true) prop attr exp =
+(** Set an attribute associated to the argument expressions *)
+let set_attribute ?(footprint = false) ?(polarity = true) prop attr args =
   prop_atom_and ~footprint prop
-    (if polarity then Sil.Apred (attr, exp) else Sil.Anpred (attr, exp))
+    (if polarity then Sil.Apred (attr, args) else Sil.Anpred (attr, args))
 
 (** Replace an attribute associated to the expression *)
-let add_or_replace_exp_attribute_check_changed check_attribute_change prop atom0 =
+let add_or_replace_attribute_check_changed check_attribute_change prop atom0 =
   match atom0 with
-  | Sil.Apred (att0, exp0) | Anpred (att0, exp0) ->
-      let nexp = exp_normalize_prop prop exp0 in
-      let atom = Sil.atom_replace_exp [(exp0, nexp)] atom0 in
+  | Sil.Apred (att0, ((_ :: _) as exps0)) | Anpred (att0, ((_ :: _) as exps0)) ->
+      let nexps = IList.map (fun e -> exp_normalize_prop prop e) exps0 in
+      let nexp = IList.hd nexps in (* len nexps = len exps0 > 0 by match *)
+      let natom = Sil.atom_replace_exp (IList.combine exps0 nexps) atom0 in
       let atom_map = function
-        | Sil.Apred (att, exp) | Anpred (att, exp)
+        | Sil.Apred (att, exp :: _) | Anpred (att, exp :: _)
           when Sil.exp_equal nexp exp && attributes_in_same_category att att0 ->
             check_attribute_change att att0;
-            atom
-        | a ->
-            a in
+            natom
+        | atom ->
+            atom in
       let pi = get_pi prop in
       let pi' = IList.map_changed atom_map pi in
       if pi == pi'
-      then prop_atom_and prop atom
+      then prop_atom_and prop natom
       else replace_pi pi' prop
   | _ ->
       prop
 
-let add_or_replace_exp_attribute prop atom =
+let add_or_replace_attribute prop atom =
   (* wrapper for the most common case: do nothing *)
   let check_attr_changed = (fun _ _ -> ()) in
-  add_or_replace_exp_attribute_check_changed check_attr_changed prop atom
+  add_or_replace_attribute_check_changed check_attr_changed prop atom
 
 (** mark Sil.Var's or Sil.Lvar's as undefined *)
 let mark_vars_as_undefined prop vars_to_mark callee_pname ret_annots loc path_pos =
   let att_undef = Sil.Aundef (callee_pname, ret_annots, loc, path_pos) in
   let mark_var_as_undefined exp prop =
     match exp with
-    | Sil.Var _ | Lvar _ -> add_or_replace_exp_attribute prop (Apred (att_undef, exp))
+    | Sil.Var _ | Lvar _ -> add_or_replace_attribute prop (Apred (att_undef, [exp]))
     | _ -> prop in
   IList.fold_left (fun prop id -> mark_var_as_undefined id prop) prop vars_to_mark
 
@@ -1910,9 +1911,9 @@ let remove_resource_attribute ra_kind ra_res =
 
 let remove_attribute_from_exp prop atom =
   match atom with
-  | Sil.Apred (_, exp) | Anpred (_, exp) ->
-      let nexp = exp_normalize_prop prop exp in
-      let natom = Sil.atom_replace_exp [(exp,nexp)] atom in
+  | Sil.Apred (_, exps) | Anpred (_, exps) ->
+      let nexps = IList.map (fun e -> exp_normalize_prop prop e) exps in
+      let natom = Sil.atom_replace_exp (IList.combine exps nexps) atom in
       let f a = not (Sil.atom_equal natom a) in
       filter_atoms ~f prop
   | _ ->
@@ -1925,7 +1926,7 @@ let replace_objc_null prop lhs_exp rhs_exp =
       let prop = remove_attribute_from_exp prop atom in
       let prop = conjoin_eq rhs_exp Sil.exp_zero prop in
       let natom = Sil.atom_replace_exp [(rhs_exp, lhs_exp)] atom in
-      add_or_replace_exp_attribute prop natom
+      add_or_replace_attribute prop natom
   | _ -> prop
 
 let rec nullify_exp_with_objc_null prop exp =
@@ -1944,14 +1945,11 @@ let rec nullify_exp_with_objc_null prop exp =
   | _ -> prop
 
 (** Get all the attributes of the prop *)
-let get_atoms_with_attribute att prop =
-  let atom_remove atom autoreleased_atoms = match atom with
-    | Sil.Apred (att_old, e) | Anpred (att_old, e) ->
-        if Sil.attribute_equal att_old att then
-          e:: autoreleased_atoms
-        else autoreleased_atoms
-    | _ -> autoreleased_atoms in
-  IList.fold_right atom_remove (get_pi prop) []
+let get_atoms_with_attribute prop att =
+  IList.filter (function
+      | Sil.Apred (att', _) | Anpred (att', _) -> Sil.attribute_equal att' att
+      | _ -> false
+    ) (get_pi prop)
 
 (** Apply f to every resource attribute in the prop *)
 let attribute_map_resource prop f =
@@ -1959,8 +1957,8 @@ let attribute_map_resource prop f =
     | Sil.Aresource ra -> Sil.Aresource (f e ra)
     | att -> att in
   let atom_map = function
-    | Sil.Apred (att, e) -> Sil.Apred (attribute_map e att, e)
-    | Sil.Anpred (att, e) -> Sil.Anpred (attribute_map e att, e)
+    | Sil.Apred (att, ([e] as es)) -> Sil.Apred (attribute_map e att, es)
+    | Sil.Anpred (att, ([e] as es)) -> Sil.Anpred (attribute_map e att, es)
     | atom -> atom in
   replace_pi (IList.map atom_map (get_pi prop)) prop
 
@@ -1981,7 +1979,7 @@ let find_arithmetic_problem proc_node_session prop exp =
     match exp_normalize_prop prop e with
     | Sil.Const c when iszero_int_float c -> true
     | _ ->
-        res := add_or_replace_exp_attribute !res (Apred (Adiv0 proc_node_session, e));
+        res := add_or_replace_attribute !res (Apred (Adiv0 proc_node_session, [e]));
         false in
   let rec walk = function
     | Sil.Var _ -> ()
@@ -2039,7 +2037,8 @@ let deallocate_stack_vars p pvars =
       if Sil.fav_mem p'_fav freshv then (* the address of a de-allocated stack var in in the post *)
         begin
           stack_vars_address_in_post := v :: !stack_vars_address_in_post;
-          res := add_or_replace_exp_attribute !res (Apred (Adangling DAaddr_stack_var, Var freshv))
+          let pred = Sil.Apred (Adangling DAaddr_stack_var, [Sil.Var freshv]) in
+          res := add_or_replace_attribute !res pred
         end in
     IList.iter do_var !fresh_address_vars;
     !res in
@@ -2301,10 +2300,10 @@ let atom_captured_ren ren = function
       Sil.Aeq (exp_captured_ren ren e1, exp_captured_ren ren e2)
   | Sil.Aneq (e1, e2) ->
       Sil.Aneq (exp_captured_ren ren e1, exp_captured_ren ren e2)
-  | Sil.Apred (a, e) ->
-      Sil.Apred (a, exp_captured_ren ren e)
-  | Sil.Anpred (a, e) ->
-      Sil.Anpred (a, exp_captured_ren ren e)
+  | Sil.Apred (a, es) ->
+      Sil.Apred (a, IList.map (fun e -> exp_captured_ren ren e) es)
+  | Sil.Anpred (a, es) ->
+      Sil.Anpred (a, IList.map (fun e -> exp_captured_ren ren e) es)
 
 let rec strexp_captured_ren ren = function
   | Sil.Eexp (e, inst) ->

infer/src/backend/prop.mli

@@ -223,10 +223,10 @@ val mk_neq : exp -> exp -> atom
 val mk_eq : exp -> exp -> atom
 
 (** Construct a positive pred. *)
-val mk_pred : attribute -> exp -> atom
+val mk_pred : attribute -> exp list -> atom
 
 (** Construct a negative pred. *)
-val mk_npred : attribute -> exp -> atom
+val mk_npred : attribute -> exp list -> atom
 
 (** create a strexp of the given type, populating the structures if [expand_structs] is true *)
 val create_strexp_of_type :
@@ -285,10 +285,10 @@ val atom_is_attribute : atom -> bool
 val attribute_map_resource : normal t -> (Sil.exp -> Sil.res_action -> Sil.res_action) -> normal t
 
 (** Return the exp and attribute marked in the atom if any, and return None otherwise *)
-val atom_get_exp_attribute : atom -> atom option
+val atom_get_attribute : atom -> atom option
 
 (** Get the attributes associated to the expression, if any *)
-val get_exp_attributes : 'a t -> exp -> atom list
+val get_attributes : 'a t -> exp -> atom list
 
 (** Get the undef attribute associated to the expression, if any *)
 val get_undef_attribute : 'a t -> exp -> atom option
@@ -319,15 +319,15 @@ val get_all_attributes : 'a t -> atom list
 
 val has_dangling_uninit_attribute : 'a t -> exp -> bool
 
-(** Set an attribute associated to the expression *)
-val set_exp_attribute : ?footprint: bool -> ?polarity: bool ->
-  normal t -> attribute -> exp -> normal t
+(** Set an attribute associated to the argument expressions *)
+val set_attribute : ?footprint: bool -> ?polarity: bool ->
+  normal t -> attribute -> exp list -> normal t
 
-val add_or_replace_exp_attribute_check_changed :
+val add_or_replace_attribute_check_changed :
   (Sil.attribute -> Sil.attribute -> unit) -> normal t -> atom -> normal t
 
 (** Replace an attribute associated to the expression *)
-val add_or_replace_exp_attribute : normal t -> atom -> normal t
+val add_or_replace_attribute : normal t -> atom -> normal t
 
 (** mark Sil.Var's or Sil.Lvar's as undefined *)
 val mark_vars_as_undefined : normal t -> Sil.exp list -> Procname.t -> Typ.item_annotation ->
@@ -347,8 +347,8 @@ val nullify_exp_with_objc_null : normal t -> exp -> normal t
 (** Remove an attribute from an exp in the heap *)
 val remove_attribute_from_exp : 'a t -> atom -> normal t
 
-(** Retireve all the atoms in the heap that contain a specific attribute *)
-val get_atoms_with_attribute : Sil.attribute -> 'a t -> Sil.exp list
+(** Retrieve all the atoms that contain a specific attribute *)
+val get_atoms_with_attribute : 'a t -> Sil.attribute -> Sil.atom list
 
 (** Return the sub part of [prop]. *)
 val get_sub : 'a t -> subst

infer/src/backend/propgraph.ml

@@ -44,13 +44,14 @@ let edge_is_hpred = function
 
 (** Return the source of the edge *)
 let edge_get_source = function
-  | Ehpred (Sil.Hpointsto(e, _, _)) -> e
-  | Ehpred (Sil.Hlseg(_, _, e, _, _)) -> e
-  | Ehpred (Sil.Hdllseg(_, _, e1, _, _, _, _)) -> e1 (* only one direction supported for now *)
-  | Eatom (Sil.Aeq (e1, _)) -> e1
-  | Eatom (Sil.Aneq (e1, _)) -> e1
-  | Eatom (Sil.Apred (_, e) | Anpred (_, e)) -> e
-  | Esub_entry (x, _) -> Sil.Var x
+  | Ehpred (Sil.Hpointsto(e, _, _)) -> Some e
+  | Ehpred (Sil.Hlseg(_, _, e, _, _)) -> Some e
+  | Ehpred (Sil.Hdllseg(_, _, e1, _, _, _, _)) -> Some e1 (* only one direction supported for now *)
+  | Eatom (Sil.Aeq (e1, _)) -> Some e1
+  | Eatom (Sil.Aneq (e1, _)) -> Some e1
+  | Eatom (Sil.Apred (_, e :: _) | Anpred (_, e :: _)) -> Some e
+  | Eatom (Sil.Apred (_, []) | Anpred (_, [])) -> None
+  | Esub_entry (x, _) -> Some (Sil.Var x)
 
 (** Return the successor nodes of the edge *)
 let edge_get_succs = function
@@ -74,7 +75,11 @@ let edge_from_source g n footprint_part is_hpred =
     if is_hpred
     then IList.map (fun hpred -> Ehpred hpred ) (get_sigma footprint_part g)
     else IList.map (fun a -> Eatom a) (get_pi footprint_part g) @ IList.map (fun entry -> Esub_entry entry) (get_subl footprint_part g) in
-  match IList.filter (fun hpred -> Sil.exp_equal n (edge_get_source hpred)) edges with
+  let starts_from hpred =
+    match edge_get_source hpred with
+    | Some e -> Sil.exp_equal n e
+    | None -> false in
+  match IList.filter starts_from edges with
   | [] -> None
   | edge:: _ -> Some edge
 
@@ -159,10 +164,9 @@ let compute_edge_diff (oldedge: edge) (newedge: edge) : Obj.t list = match olded
       compute_exp_diff e1 e2
   | Eatom (Sil.Aneq (_, e1)), Eatom (Sil.Aneq (_, e2)) ->
       compute_exp_diff e1 e2
-  | Eatom (Sil.Apred (_, e1)), Eatom (Sil.Apred (_, e2)) ->
-      compute_exp_diff e1 e2
-  | Eatom (Sil.Anpred (_, e1)), Eatom (Sil.Anpred (_, e2)) ->
-      compute_exp_diff e1 e2
+  | Eatom (Sil.Apred (_, es1)), Eatom (Sil.Apred (_, es2))
+  | Eatom (Sil.Anpred (_, es1)), Eatom (Sil.Anpred (_, es2)) ->
+      IList.flatten (try IList.map2 compute_exp_diff es1 es2 with IList.Fail -> [])
   | Esub_entry (_, e1), Esub_entry (_, e2) ->
       compute_exp_diff e1 e2
   | _ -> [Obj.repr newedge]
@@ -173,8 +177,10 @@ let compute_diff default_color oldgraph newgraph : diff =
     let newedges = get_edges footprint_part newgraph in
     let changed = ref [] in
     let build_changed edge =
-      if not (contains_edge footprint_part oldgraph edge) then begin
-        match edge_from_source oldgraph (edge_get_source edge) footprint_part (edge_is_hpred edge) with
+      if not (contains_edge footprint_part oldgraph edge) then
+        match edge_get_source edge with
+        | Some source -> (
+            match edge_from_source oldgraph source footprint_part (edge_is_hpred edge) with
             | None ->
                 let changed_obj = match edge with
                   | Ehpred hpred -> Obj.repr hpred
@@ -182,7 +188,9 @@ let compute_diff default_color oldgraph newgraph : diff =
                   | Esub_entry entry -> Obj.repr entry in
                 changed := changed_obj :: !changed
             | Some oldedge -> changed := compute_edge_diff oldedge edge @ !changed
-      end in
+          )
+        | None ->
+            () in
     IList.iter build_changed newedges;
     let colormap (o: Obj.t) =
       if IList.exists (fun x -> x == o) !changed then Red

infer/src/backend/propgraph.mli

@@ -28,7 +28,7 @@ val is_root : node -> bool
 val nodes_connected : node -> node -> bool
 
 (** Return the source of the edge *)
-val edge_get_source : edge -> node
+val edge_get_source : edge -> node option
 
 (** Return the successor nodes of the edge *)
 val edge_get_succs : edge -> node list

infer/src/backend/prover.ml

@@ -2109,14 +2109,12 @@ let rec pre_check_pure_implication calc_missing subs pi1 pi2 =
              imply_atom calc_missing subs prop_for_impl (Sil.Aeq (e2_in, f2_in));
              pre_check_pure_implication calc_missing subs pi1 pi2'
         )
-  | Sil.Aeq _ :: pi2' -> (* must be an inequality *)
-      pre_check_pure_implication calc_missing subs pi1 pi2'
-  | (Sil.Aneq (e, _) | Apred (_, e) | Anpred (_, e)) :: pi2' ->
-      if calc_missing || (match e with Var v -> Ident.is_primed v | _ -> false) then
-        pre_check_pure_implication calc_missing subs pi1 pi2'
-      else
+  | (Sil.Aneq (e, _) | Apred (_, e :: _) | Anpred (_, e :: _)) :: _
+    when not calc_missing && (match e with Var v -> not (Ident.is_primed v) | _ -> true) ->
       raise (IMPL_EXC ("ineq e2=f2 in rhs with e2 not primed var",
                        (Sil.sub_empty, Sil.sub_empty), EXC_FALSE))
+  | (Sil.Aeq _ | Aneq _ | Apred _ | Anpred _) :: pi2' ->
+      pre_check_pure_implication calc_missing subs pi1 pi2'
 
 (** Perform the array bound checks delayed (to instantiate variables) by the prover.
     If there is a provable violation of the array bounds, set the prover status to Bounds_check

infer/src/backend/rearrange.ml

@@ -746,7 +746,7 @@ let add_guarded_by_constraints prop lexp pdesc =
         (function
           | Sil.Apred (Alocked, _) -> true
           | _ -> false)
-        (Prop.get_exp_attributes prop guarded_by_exp) in
+        (Prop.get_attributes prop guarded_by_exp) in
     let should_warn pdesc =
       (* adding this check implements "by reference" semantics for guarded-by rather than "by value"
          semantics. if this access is through a local L or field V.f
@@ -793,7 +793,7 @@ let add_guarded_by_constraints prop lexp pdesc =
           end
         else
           (* private method. add locked proof obligation to [pdesc] *)
-          Prop.set_exp_attribute ~footprint:true prop Alocked guarded_by_exp
+          Prop.set_attribute ~footprint:true prop Alocked [guarded_by_exp]
     | _ ->
         if not (proc_has_matching_annot pdesc guarded_by_str
                 || is_synchronized_on_class guarded_by_str) && should_warn pdesc
@@ -1205,7 +1205,7 @@ let check_dereference_error pdesc (prop : Prop.normal Prop.t) lexp loc =
                        nullable_obj_str := Some (Procname.to_string pname);
                        true
                    | _ -> false in
-                 IList.exists is_nullable_attr (Prop.get_exp_attributes prop exp) in
+                 IList.exists is_nullable_attr (Prop.get_attributes prop exp) in
              (* it's ok for a non-nullable local to point to deref_exp *)
              is_nullable || Pvar.is_local pvar
          | Sil.Hpointsto (_, Sil.Estruct (flds, _), Sil.Sizeof (typ, _, _)) ->

infer/src/backend/symExec.ml

@@ -476,11 +476,11 @@ let check_already_dereferenced pname cond prop =
     raising an exception in that case *)
 let check_deallocate_static_memory prop_after =
   let check_deallocated_attribute = function
-    | Sil.Apred (Aresource ({ ra_kind = Rrelease } as ra), Lvar pv)
+    | Sil.Apred (Aresource ({ ra_kind = Rrelease } as ra), [Lvar pv])
       when Pvar.is_local pv || Pvar.is_global pv ->
         let freed_desc = Errdesc.explain_deallocate_stack_var pv ra in
         raise (Exceptions.Deallocate_stack_variable freed_desc)
-    | Sil.Apred (Aresource ({ ra_kind = Rrelease } as ra), Const (Cstr s)) ->
+    | Sil.Apred (Aresource ({ ra_kind = Rrelease } as ra), [Const (Cstr s)]) ->
         let freed_desc = Errdesc.explain_deallocate_constant_string s ra in
         raise (Exceptions.Deallocate_static_memory freed_desc)
     | _ -> () in
@@ -738,7 +738,7 @@ let handle_objc_instance_method_call_or_skip actual_pars path callee_pname pre r
     | [ret_id] -> (
         match Prop.find_equal_formal_path receiver prop with
         | Some (v,fs) ->
-            Prop.add_or_replace_exp_attribute prop (Apred (Aobjc_null (v,fs), Var ret_id))
+            Prop.add_or_replace_attribute prop (Apred (Aobjc_null (v,fs), [Sil.Var ret_id]))
         | None ->
             Prop.conjoin_eq (Sil.Var ret_id) Sil.exp_zero prop
       )
@@ -843,7 +843,7 @@ let add_constraints_on_retval pdesc prop ret_exp ~has_nullable_annot typ callee_
         | Typ.Tptr _ -> Prop.conjoin_neq exp Sil.exp_zero prop
         | _ -> prop in
     let add_tainted_post ret_exp callee_pname prop =
-      Prop.add_or_replace_exp_attribute prop (Apred (Ataint callee_pname, ret_exp)) in
+      Prop.add_or_replace_attribute prop (Apred (Ataint callee_pname, [ret_exp])) in
 
     if Config.angelic_execution && not (is_rec_call callee_pname) then
       (* introduce a fresh program variable to allow abduction on the return value *)
@@ -872,7 +872,7 @@ let add_taint prop lhs_id rhs_exp pname tenv  =
     if Taint.has_taint_annotation fieldname struct_typ
     then
       let taint_info = { Sil.taint_source = pname; taint_kind = Tk_unknown; } in
-      Prop.add_or_replace_exp_attribute prop (Apred (Ataint taint_info, Var lhs_id))
+      Prop.add_or_replace_attribute prop (Apred (Ataint taint_info, [Sil.Var lhs_id]))
     else
       prop in
   match rhs_exp with
@@ -903,7 +903,7 @@ let execute_letderef ?(report_deref_errors=true) pname pdesc tenv id rhs_exp typ
           let prop' = Prop.prop_iter_to_prop iter' in
           let prop'' =
             if lookup_uninitialized then
-              Prop.add_or_replace_exp_attribute prop' (Apred (Adangling DAuninit, Var id))
+              Prop.add_or_replace_attribute prop' (Apred (Adangling DAuninit, [Sil.Var id]))
             else prop' in
           let prop''' =
             if Config.taint_analysis
@@ -936,7 +936,7 @@ let execute_letderef ?(report_deref_errors=true) pname pdesc tenv id rhs_exp typ
             match callee_opt, atom with
             | None, Sil.Apred (Aundef _, _) -> Some atom
             | _ -> callee_opt in
-          IList.fold_left fold_undef_pname None (Prop.get_exp_attributes prop exp) in
+          IList.fold_left fold_undef_pname None (Prop.get_attributes prop exp) in
         let prop' =
           if Config.angelic_execution then
             (* when we try to deref an undefined value, add it to the footprint *)
@@ -1375,12 +1375,12 @@ and check_untainted exp taint_kind caller_pname callee_pname prop =
         Exceptions.Tainted_value_reaching_sensitive_function
           (err_desc, __POS__) in
       Reporting.log_warning caller_pname exn;
-      Prop.add_or_replace_exp_attribute prop (Apred (Auntaint taint_info, exp))
+      Prop.add_or_replace_attribute prop (Apred (Auntaint taint_info, [exp]))
   | _ ->
       if !Config.footprint then
         let taint_info = { Sil.taint_source = callee_pname; taint_kind; } in
         (* add untained(n_lexp) to the footprint *)
-        Prop.set_exp_attribute ~footprint:true prop (Auntaint taint_info) exp
+        Prop.set_attribute ~footprint:true prop (Auntaint taint_info) [exp]
       else prop
 
 (** execute a call for an unknown or scan function *)
@@ -1393,7 +1393,7 @@ and unknown_or_scan_call ~is_scan ret_type_option ret_annots
         match atom with
         | Sil.Apred ((Aresource {ra_res = Rfile} as res), _) -> Prop.remove_attribute q res
         | _ -> q in
-      IList.fold_left do_attribute p (Prop.get_exp_attributes p e) in
+      IList.fold_left do_attribute p (Prop.get_attributes p e) in
     let filtered_args =
       match args, instr with
       | _:: other_args, Sil.Call (_, _, _, _, { CallFlags.cf_virtual }) when cf_virtual ->

infer/src/backend/tabulation.ml

@@ -362,7 +362,7 @@ let post_process_sigma (sigma: Sil.hpred list) loc : Sil.hpred list =
 let check_path_errors_in_post caller_pname post post_path =
   let check_attr atom =
     match atom with
-    | Sil.Apred (Adiv0 path_pos, e) ->
+    | Sil.Apred (Adiv0 path_pos, [e]) ->
         if Prover.check_zero e then
           let desc = Errdesc.explain_divide_by_zero e (State.get_node ()) (State.get_loc ()) in
           let new_path, path_pos_opt =
@@ -386,12 +386,12 @@ let post_process_post
     | Some (Apred (Aresource ({ ra_kind = Rrelease }), _)) -> true
     | _ -> false in
   let atom_update_alloc_attribute = function
-    | Sil.Apred (Aresource ra, e)
+    | Sil.Apred (Aresource ra, [e])
       when not (ra.Sil.ra_kind = Sil.Rrelease && actual_pre_has_freed_attribute e) ->
         (* unless it was already freed before the call *)
         let vpath, _ = Errdesc.vpath_find post e in
         let ra' = { ra with Sil.ra_pname = callee_pname; Sil.ra_loc = loc; Sil.ra_vpath = vpath } in
-        Sil.Apred (Aresource ra', e)
+        Sil.Apred (Aresource ra', [e])
     | a -> a in
   let prop' = Prop.replace_sigma (post_process_sigma (Prop.get_sigma post) loc) post in
   let pi' = IList.map atom_update_alloc_attribute (Prop.get_pi prop') in
@@ -603,10 +603,10 @@ let prop_copy_footprint_pure p1 p2 =
   let res_noattr = Prop.replace_pi (Prop.get_pure p1 @ pi2_noattr) p2' in
   let replace_attr prop atom = (* call replace_atom_attribute which deals with existing attibutes *)
     (* if [atom] represents an attribute [att], add the attribure to [prop] *)
-    match Prop.atom_get_exp_attribute atom with
+    match Prop.atom_get_attribute atom with
     | None -> prop
     | Some atom ->
-        Prop.add_or_replace_exp_attribute_check_changed check_attr_dealloc_mismatch prop atom in
+        Prop.add_or_replace_attribute_check_changed check_attr_dealloc_mismatch prop atom in
   IList.fold_left replace_attr (Prop.normalize res_noattr) pi2_attr
 
 (** check if an expression is an exception *)
@@ -884,7 +884,7 @@ let mk_posts ret_ids prop callee_pname callee_attrs posts =
         let last_call_ret_non_null =
           IList.exists
             (function
-              | Sil.Apred (Aretval (pname, _), exp) when Procname.equal callee_pname pname ->
+              | Sil.Apred (Aretval (pname, _), [exp]) when Procname.equal callee_pname pname ->
                   Prover.check_disequal prop exp Sil.exp_zero
               | _ -> false)
             (Prop.get_all_attributes prop) in
@@ -904,8 +904,8 @@ let mk_posts ret_ids prop callee_pname callee_attrs posts =
             let taint_retval (prop, path) =
               let prop_normal = Prop.normalize prop in
               let prop' =
-                Prop.add_or_replace_exp_attribute prop_normal
-                  (Apred (Ataint { taint_source = callee_pname; taint_kind; }, Var ret_id))
+                Prop.add_or_replace_attribute prop_normal
+                  (Apred (Ataint { taint_source = callee_pname; taint_kind; }, [Sil.Var ret_id]))
                 |> Prop.expose in
               (prop', path) in
             IList.map taint_retval posts
@@ -936,11 +936,11 @@ let do_taint_check caller_pname callee_pname calling_prop missing_pi sub actual_
   (* build a map from exp -> [taint attrs, untaint attrs], keeping only exprs with both kinds of
      attrs (we will flag errors on those exprs) *)
   let collect_taint_untaint_exprs acc_map atom =
-    match Prop.atom_get_exp_attribute atom with
-    | Some (Apred (Ataint _, e)) ->
+    match Prop.atom_get_attribute atom with
+    | Some (Apred (Ataint _, [e])) ->
         let taint_atoms, untaint_atoms = try Sil.ExpMap.find e acc_map with Not_found -> ([], []) in
         Sil.ExpMap.add e (atom :: taint_atoms, untaint_atoms) acc_map
-    | Some (Apred (Auntaint _, e)) ->
+    | Some (Apred (Auntaint _, [e])) ->
         let taint_atoms, untaint_atoms = try Sil.ExpMap.find e acc_map with Not_found -> ([], []) in
         Sil.ExpMap.add e (taint_atoms, atom :: untaint_atoms) acc_map
     | _ -> acc_map in
@@ -955,7 +955,7 @@ let do_taint_check caller_pname callee_pname calling_prop missing_pi sub actual_
      the untaint atoms *)
   let report_taint_errors e (taint_atoms, _untaint_atoms) =
     let report_one_error taint_atom =
-      let taint_info = match Prop.atom_get_exp_attribute taint_atom with
+      let taint_info = match Prop.atom_get_attribute taint_atom with
         | Some (Apred (Ataint taint_info, _)) -> taint_info
         | _ -> failwith "Expected to get taint attr on atom" in
       report_taint_error e taint_info callee_pname caller_pname calling_prop in
@@ -1262,7 +1262,7 @@ let exe_call_postprocess ret_ids trace_call callee_pname callee_attrs loc result
       let ret_var = Sil.Var ret_id in
       let mark_id_as_retval (p, path) =
         let att_retval = Sil.Aretval (callee_pname, ret_annot) in
-        Prop.set_exp_attribute p att_retval ret_var, path in
+        Prop.set_attribute p att_retval [ret_var], path in
       IList.map mark_id_as_retval res
   | _ -> res
 

infer/src/backend/taint.ml

@@ -379,6 +379,6 @@ let add_tainting_attribute att pvar_param prop =
          when Pvar.equal pvar pvar_param ->
            L.d_strln ("TAINT ANALYSIS: setting taint/untaint attribute of parameter " ^
                       (Pvar.to_string pvar));
-           Prop.add_or_replace_exp_attribute prop_acc (Apred (att, rhs))
+           Prop.add_or_replace_attribute prop_acc (Apred (att, [rhs]))
        | _ -> prop_acc)
     prop (Prop.get_sigma prop)