Add a config option to whitelist common initializer values for liveness analysis (#1340)

Summary:
Implements https://github.com/facebook/infer/issues/1083

Pull Request resolved: https://github.com/facebook/infer/pull/1340

Reviewed By: mityal

Differential Revision: D24956747

Pulled By: jvillard

fbshipit-source-id: 820eb538a

infer/man/man1/infer-analyze.txt

@@ -200,6 +200,9 @@ OPTIONS
            Deactivates: checker liveness: Detection of dead stores and unused
            variables. (Conversely: --liveness)
 
+       --liveness-ignored-constant +string
+           List of integer constants to be ignored by liveness analysis
+
        --liveness-only
            Activates: Enable liveness and disable all other checkers
            (Conversely: --no-liveness-only)

infer/man/man1/infer-full.txt

@@ -790,6 +790,10 @@ OPTIONS
            unique_ptr<type>) will count as dead stores when the variables are
            not read explicitly by the program.           See also infer-analyze(1).
 
+       --liveness-ignored-constant +string
+           List of integer constants to be ignored by liveness analysis       
+    See also infer-analyze(1).
+
        --liveness-only
            Activates: Enable liveness and disable all other checkers
            (Conversely: --no-liveness-only)           See also infer-analyze(1).
@@ -1597,6 +1601,9 @@ INTERNAL OPTIONS
        --linters-doc-url-reset
            Set --linters-doc-url to the empty list.
 
+       --liveness-ignored-constant-reset
+           Set --liveness-ignored-constant to the empty list.
+
        --load-average-reset
            Cancel the effect of --load-average.
 

infer/man/man1/infer.txt

@@ -790,6 +790,10 @@ OPTIONS
            unique_ptr<type>) will count as dead stores when the variables are
            not read explicitly by the program.           See also infer-analyze(1).
 
+       --liveness-ignored-constant +string
+           List of integer constants to be ignored by liveness analysis       
+    See also infer-analyze(1).
+
        --liveness-only
            Activates: Enable liveness and disable all other checkers
            (Conversely: --no-liveness-only)           See also infer-analyze(1).

infer/src/base/Config.ml

@@ -1497,6 +1497,12 @@ and liveness_dangerous_classes =
      by the program."
 
 
+and liveness_ignored_constant =
+  CLOpt.mk_string_list ~default:["0"] ~long:"liveness-ignored-constant"
+    ~in_help:InferCommand.[(Analyze, manual_generic)]
+    "List of integer constants to be ignored by liveness analysis"
+
+
 and _log_events =
   CLOpt.mk_bool ~long:"" ~deprecated:["-log-events"] ~deprecated_no:["-no-log-events"]
     "[DOES NOTHING] Turn on the feature that logs events in a machine-readable format"
@@ -2962,6 +2968,8 @@ and list_issue_types = !list_issue_types
 
 and liveness_dangerous_classes = !liveness_dangerous_classes
 
+and liveness_ignored_constant = !liveness_ignored_constant
+
 and load_average =
   match !load_average with None when !buck -> Some (float_of_int ncpu) | _ -> !load_average
 

infer/src/base/Config.mli

@@ -376,6 +376,8 @@ val list_issue_types : bool
 
 val liveness_dangerous_classes : Yojson.Basic.t
 
+val liveness_ignored_constant : string list
+
 val max_nesting : int option
 
 val merge : bool

infer/src/checkers/liveness.ml

@@ -212,6 +212,21 @@ let get_captured_by_ref_invariant_map proc_desc =
   CapturedByRefAnalyzer.exec_cfg cfg () ~initial:VarSet.empty
 
 
+module IntLitSet = Caml.Set.Make (IntLit)
+
+let ignored_constants =
+  let int_lit_constants =
+    List.map
+      ~f:(fun el ->
+        try IntLit.of_string el
+        with Invalid_argument _ ->
+          L.die UserError
+            "Ill-formed option  '%s' for --liveness-ignored-constant: an integer was expected" el )
+      Config.liveness_ignored_constant
+  in
+  IntLitSet.of_list int_lit_constants
+
+
 let checker {IntraproceduralAnalysis.proc_desc; err_log} =
   let captured_by_ref_invariant_map = get_captured_by_ref_invariant_map proc_desc in
   let cfg = CFG.from_pdesc proc_desc in
@@ -223,9 +238,13 @@ let checker {IntraproceduralAnalysis.proc_desc; err_log} =
     | Exp.Cast (_, e) ->
         is_sentinel_exp e
     | Exp.Const (Cint i) ->
-        IntLit.iszero i || IntLit.isnull i
-    | Exp.Const (Cfloat 0.0) ->
-        true
+        IntLitSet.mem i ignored_constants
+    | Exp.Const (Cfloat f) -> (
+      match Z.of_float f with
+      | z ->
+          IntLitSet.mem (IntLit.of_big_int z) ignored_constants
+      | exception Z.Overflow ->
+          false )
     | _ ->
         false
   in

infer/tests/codetoanalyze/cpp/liveness/.inferconfig

@@ -1,4 +1,5 @@
 {
+  "liveness-ignored-constant" : ["44"],
   "liveness-dangerous-classes": [
     "dead_stores::BlacklistedStruct"
   ],

infer/tests/codetoanalyze/cpp/liveness/dead_stores.cpp

@@ -609,4 +609,10 @@ void switch_with_temporary_ok() {
   };
 }
 
+void ignored_constants_ok() {
+  int x = 0;
+  float f = 0.0;
+  int z = 44;
+}
+
 } // namespace dead_stores