widen for access trees

Reviewed By: jberdine

Differential Revision: D3605415

fbshipit-source-id: 26f1eec

infer/src/checkers/accessTree.ml

@@ -236,6 +236,42 @@ module Make (TraceDomain : AbstractDomain.S) = struct
             node_opt in
       BaseMap.merge (fun _ n1 n2 -> node_merge n1 n2) tree1 tree2
 
+  (* replace the normal leaves of [node] with starred leaves *)
+  let rec node_add_stars ((trace, tree) as node) = match tree with
+    | Subtree subtree ->
+        if AccessMap.is_empty subtree
+        then make_starred_leaf trace
+        else
+          let subtree' = AccessMap.map node_add_stars subtree in
+          if subtree' == subtree
+          then node
+          else trace, Subtree subtree'
+    | Star -> node
+
+  let widen ~prev ~next ~num_iters =
+    if prev == next
+    then prev
+    else
+      let trace_widen prev next =
+        TraceDomain.widen ~prev ~next ~num_iters in
+      let rec node_widen prev_node_opt next_node_opt =
+        match prev_node_opt, next_node_opt with
+        | Some prev_node, Some next_node ->
+            let widened_node = node_join node_widen trace_widen prev_node next_node in
+            if widened_node == prev_node
+            then prev_node_opt
+            else if widened_node == next_node
+            then next_node_opt
+            else Some widened_node
+        | None, Some next_node ->
+            let widened_node = node_add_stars next_node in
+            if widened_node == next_node
+            then next_node_opt
+            else Some widened_node
+        | Some _, None | None, None ->
+            prev_node_opt in
+      BaseMap.merge (fun _ prev_node next_node -> node_widen prev_node next_node) prev next
+
   let pp fmt base_tree =
     let rec pp_node fmt (trace, subtree) =
       let pp_subtree fmt = function

infer/src/unit/accessTreeTests.ml

@@ -12,13 +12,42 @@ open !Utils
 module F = Format
 
 (* string set domain we use to ensure we're getting the expected traces *)
-module MockTraceDomain =
-  AbstractDomain.FiniteSet
+module MockTraceDomain = struct
+  include AbstractDomain.FiniteSet
     (PrettyPrintable.MakePPSet(struct
        include String
        let pp_element fmt s = Format.fprintf fmt "%s" s
      end))
 
+  let top_str = "T"
+
+  let top = singleton top_str
+
+  (* stop others from creating top by accident, adding to top, or removing it *)
+  let add e s =
+    assert (e <> top_str);
+    if s == top
+    then top
+    else add e s
+
+  let singleton e =
+    assert (e <> top_str);
+    singleton e
+
+  (* total hack of a widening just to test that widening of traces is working *)
+  let widen ~prev ~next ~num_iters:_ =
+    let trace_diff = diff next prev in
+    if not (is_empty trace_diff)
+    then top
+    else join prev next
+
+  (* similarly, hack printing so top looks different *)
+  let pp fmt s =
+    if s == top
+    then F.fprintf fmt "T"
+    else pp fmt s
+end
+
 module Domain = AccessTree.Make (MockTraceDomain)
 
 let assert_trees_equal tree1 tree2 =
@@ -300,4 +329,57 @@ let tests =
       assert_trees_equal (Domain.join x_star_tree xFG_tree) x_star_tree_xFG_trace in
     "join">::join_test_ in
 
-  "access_tree_suite">:::[get_trace_test; add_trace_test; lteq_test; join_test]
+  let widen_test =
+    let widen_test_ _ =
+      let make_x_base_tree trace =
+        Domain.BaseMap.singleton x_base (Domain.make_normal_leaf trace) in
+      let widen prev next =
+        Domain.widen ~prev ~next ~num_iters:0 in
+      (* a bit light on the tests here, since widen is implemented as a simple wrapper of join *)
+
+      (* widening traces works:
+         x |-> ("x", empty) \/ x |-> ("y", empty) =
+         x |-> (T, empty)
+      *)
+      let x_tree_x_trace = make_x_base_tree x_trace in
+      let x_tree_y_trace = make_x_base_tree y_trace in
+      let x_tree_top_trace = make_x_base_tree MockTraceDomain.top in
+      assert_trees_equal (widen x_tree_x_trace x_tree_y_trace) x_tree_top_trace;
+
+      (* adding stars to a base works:
+         x |-> ({}, empty) \/ y |-> ({}, empty) =
+         (x |-> ({}, empty), y |-> ({}, Star) )
+      *)
+      let x_y_star_base_tree =
+        Domain.BaseMap.add
+          y_base
+          (Domain.make_starred_leaf MockTraceDomain.initial)
+          x_base_tree in
+      assert_trees_equal (widen x_base_tree y_base_tree) x_y_star_base_tree;
+
+      (* adding stars to a subtree works:
+         x |-> ("y", empty) \/
+         x |-> ("x" , f |-> ("f", g |-> ("g", empty))) =
+         x |-> (T , f |-> ("f", g |-> ("g", Star)))
+      *)
+      let xFG_star_tree =
+        let g_subtree = Domain.make_starred_leaf xFG_trace in
+        Domain.AccessMap.singleton g g_subtree
+        |> Domain.make_node xF_trace
+        |> Domain.AccessMap.singleton f
+        |> Domain.make_node MockTraceDomain.top
+        |> Domain.BaseMap.singleton x_base in
+      assert_trees_equal (widen x_tree_y_trace xFG_tree) xFG_star_tree;
+
+      (* widening is not commutative, and is it not join:
+         x |-> ("x" , f |-> ("f", g |-> ("g", empty))) \/
+         x |-> ("y", empty) =
+         x |-> (T , f |-> ("f", g |-> ("g", empty)))
+      *)
+      let xFG_tree_widened_trace =
+        let _, xFG_node = x_subtree in
+        Domain.BaseMap.singleton x_base (MockTraceDomain.top, xFG_node) in
+      assert_trees_equal (widen xFG_tree x_tree_y_trace) xFG_tree_widened_trace in
+    "widen">::widen_test_ in
+
+  "access_tree_suite">:::[get_trace_test; add_trace_test; lteq_test; join_test; widen_test]