[dead store] Removed special case for constexpr in lambda captures

Summary: We had a special case for fixing false positives on constexpr implicitly captured by lambdas. However, we do not report dead stores on constexpr anymore, hence, do not need the special case anymore. Moreover, the special case was not only capturing constexpr in lambdas, but also any variables which type had `const` (see new test `capture_const_bad` which was not being reported before this diff)

Reviewed By: mbouaziz

Differential Revision: D9654848

fbshipit-source-id: 882fd2804

infer/src/checkers/liveness.ml

@@ -48,27 +48,7 @@ module TransferFunctions (CFG : ProcCfg.S) = struct
         add_live_actuals_ actuals live_acc
 
 
-  (* In C++14, for a lambda at block scope, constexpr variables in the
+  let exec_instr astate _ _ = function
-     reaching scope may be used inside the lambda, even if they are
-     not captured.  For further details:
-     https://timsong-cpp.github.io/cppwp/n4140/expr.prim.lambda#12 *)
-  let add_local_consts_for_lambdas pdesc call_exp astate =
-    let pname = Procdesc.get_proc_name pdesc in
-    match call_exp with
-    | Exp.Const (Cfun (Typ.Procname.ObjC_Cpp cpp_pname))
-      when Typ.Procname.ObjC_Cpp.is_cpp_lambda cpp_pname ->
-        Procdesc.get_locals pdesc
-        |> List.fold ~init:astate ~f:(fun acc var_data ->
-               let open ProcAttributes in
-               if Typ.is_const var_data.typ.quals then
-                 let const_local_var = Pvar.mk var_data.name pname |> Var.of_pvar in
-                 Domain.add const_local_var acc
-               else acc )
-    | _ ->
-        astate
-
-
-  let exec_instr astate {ProcData.pdesc} _ = function
     | Sil.Load (lhs_id, _, _, _) when Ident.is_none lhs_id ->
         (* dummy deref inserted by frontend--don't count as a read *)
         astate
@@ -87,7 +67,6 @@ module TransferFunctions (CFG : ProcCfg.S) = struct
     | Sil.Call ((ret_id, _), call_exp, actuals, _, _) ->
         Domain.remove (Var.of_id ret_id) astate
         |> exp_add_live call_exp |> add_live_actuals actuals call_exp
-        |> add_local_consts_for_lambdas pdesc call_exp
     | Sil.Remove_temps _ | Abstract _ | Nullify _ ->
         astate
 

infer/tests/codetoanalyze/cpp/liveness/dead_stores_constexpr.cpp

@@ -17,7 +17,7 @@ void capture_constexpr_good() {
 
 void call_it(void (*f)(void)) { f(); }
 
-void FP_capture_constexpr_good() {
+void capture_constexpr2_good() {
   constexpr int x = 1;
   auto lambda = []() {
     foo(x);
@@ -26,6 +26,14 @@ void FP_capture_constexpr_good() {
   call_it(lambda);
 }
 
+void capture_const_bad(const int y) {
+  const int x = y;
+  []() {
+    foo(0);
+    return;
+  }();
+}
+
 // we always assume const exprs are captured in lambdas
 void FN_capture_constexpr_good() {
   constexpr int x = 10;

infer/tests/codetoanalyze/cpp/liveness/issues.exp

@@ -18,5 +18,6 @@ codetoanalyze/cpp/liveness/dead_stores.cpp, dead_stores::plus_plus2_bad, 2, DEAD
 codetoanalyze/cpp/liveness/dead_stores.cpp, dead_stores::plus_plus3_bad, 2, DEAD_STORE, no_bucket, ERROR, [Write of unused value]
 codetoanalyze/cpp/liveness/dead_stores.cpp, dead_stores::reassign_param_bad, 0, DEAD_STORE, no_bucket, ERROR, [Write of unused value]
 codetoanalyze/cpp/liveness/dead_stores.cpp, dead_stores::use_then_dead_bad, 3, DEAD_STORE, no_bucket, ERROR, [Write of unused value]
+codetoanalyze/cpp/liveness/dead_stores_constexpr.cpp, capture_const_bad, 1, DEAD_STORE, no_bucket, ERROR, [Write of unused value]
 codetoanalyze/cpp/liveness/non_type_template_param.cpp, X<3>_isZeroBad, 1, DEAD_STORE, no_bucket, ERROR, [Write of unused value]
 codetoanalyze/cpp/liveness/non_type_template_param.cpp, instanciateTemplateBad, 3, DEAD_STORE, no_bucket, ERROR, [Write of unused value]