[impurity] Refactor and ignore invalidations to constant dereferences

Summary:
- ignore  `ConstantDereference` invalidations since they just represent assignments to constants.
- add `impurity.mli`
- split `extract_impurity` into several sub functions.

Reviewed By: jvillard

Differential Revision: D20335674

fbshipit-source-id: f0fd6b5f4

infer/src/checkers/impurity.ml

@@ -12,9 +12,6 @@ open PulseDomainInterface
 
 let debug fmt = L.(debug Analysis Verbose fmt)
 
-(* An impurity analysis that relies on pulse to determine how the state
-   changes *)
-
 let get_matching_dest_addr_opt ~edges_pre ~edges_post : AbstractValue.t list option =
   match
     List.fold2 ~init:(Some [])
@@ -37,23 +34,19 @@ let add_invalid_and_modified ~check_empty attrs acc =
     Attributes.get_written_to attrs
     |> Option.value_map ~default:[] ~f:(fun modified -> [ImpurityDomain.WrittenTo modified])
   in
-  let res =
-    Attributes.get_invalid attrs
-    |> Option.value_map ~default:modified ~f:(fun invalid ->
-           ImpurityDomain.Invalid invalid :: modified )
+  let invalid_and_modified =
+    match Attributes.get_invalid attrs with
+    | None | Some (PulseInvalidation.ConstantDereference _, _) ->
+        modified
+    | Some invalid ->
+        ImpurityDomain.Invalid invalid :: modified
   in
-  if check_empty && List.is_empty res then
+  if check_empty && List.is_empty invalid_and_modified then
     L.(die InternalError) "Address is modified without being written to or invalidated."
-  else res @ acc
+  else invalid_and_modified @ acc
 
 
-(** Given Pulse summary, extract impurity info, i.e. parameters and global variables that are
-    modified by the function and skipped functions. *)
-let extract_impurity tenv pdesc pre_post : ImpurityDomain.t =
-  let pre_heap = (AbductiveDomain.extract_pre pre_post).BaseDomain.heap in
-  let post = AbductiveDomain.extract_post pre_post in
-  let post_stack = post.BaseDomain.stack in
-  let add_to_modified var addr acc =
+let add_to_modified var addr pre_heap post acc =
   let rec aux acc ~addr_to_explore ~visited : ImpurityDomain.trace list =
     match addr_to_explore with
     | [] ->
@@ -90,28 +83,39 @@ let extract_impurity tenv pdesc pre_post : ImpurityDomain.t =
       acc
   | hd :: tl ->
       ImpurityDomain.ModifiedVarSet.add {var; trace_list= (hd, tl)} acc
-  in
-  let pname = Procdesc.get_proc_name pdesc in
-  let modified_params =
-    Procdesc.get_formals pdesc
-    |> List.fold_left ~init:ImpurityDomain.ModifiedVarSet.empty ~f:(fun acc (name, typ) ->
+
+
+let get_modified_params pname post_stack pre_heap post formals =
+  List.fold_left formals ~init:ImpurityDomain.ModifiedVarSet.empty ~f:(fun acc (name, typ) ->
       let var = Var.of_pvar (Pvar.mk name pname) in
       match BaseStack.find_opt var post_stack with
       | Some (addr, _) when Typ.is_pointer typ -> (
         match BaseMemory.find_opt addr pre_heap with
         | Some edges_pre ->
             BaseMemory.Edges.fold
-                   (fun _ (addr, _) acc -> add_to_modified var addr acc)
+              (fun _ (addr, _) acc -> add_to_modified var addr pre_heap post acc)
               edges_pre acc
         | None ->
             debug "The address is not materialized in pre-heap." ;
             acc )
       | _ ->
           acc )
+
+
+(** Given Pulse summary, extract impurity info, i.e. parameters and global variables that are
+    modified by the function and skipped functions. *)
+let extract_impurity tenv pdesc pre_post : ImpurityDomain.t =
+  let pre_heap = (AbductiveDomain.extract_pre pre_post).BaseDomain.heap in
+  let post = AbductiveDomain.extract_post pre_post in
+  let post_stack = post.BaseDomain.stack in
+  let pname = Procdesc.get_proc_name pdesc in
+  let modified_params =
+    Procdesc.get_formals pdesc |> get_modified_params pname post_stack pre_heap post
   in
   let modified_globals =
     BaseStack.fold
-      (fun var (addr, _) acc -> if Var.is_global var then add_to_modified var addr acc else acc)
+      (fun var (addr, _) acc ->
+        if Var.is_global var then add_to_modified var addr pre_heap post acc else acc )
       post_stack ImpurityDomain.ModifiedVarSet.empty
   in
   let is_modeled_pure pname =

infer/src/checkers/impurity.mli

@@ -0,0 +1,11 @@
+(*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *)
+
+open! IStd
+
+val checker : Callbacks.proc_callback_t
+(** An impurity analysis that relies on pulse summaries to determine how the state changes *)