From 25d9f940fe27b0935c35a1cad42875d84a8386ec Mon Sep 17 00:00:00 2001
From: Sam Blackshear <shb@fb.com>
Date: Tue, 1 Aug 2017 14:46:50 -0700
Subject: [PATCH] [dead stores] fix FPs due to capture by ref

Reviewed By: jeremydubreil

Differential Revision: D5534605

fbshipit-source-id: e8048a5
---
 infer/src/checkers/liveness.ml                | 15 +++++++++-
 .../cpp/liveness/dead_stores.cpp              | 30 ++++++++++++++++++-
 .../codetoanalyze/cpp/liveness/issues.exp     |  2 +-
 3 files changed, 44 insertions(+), 3 deletions(-)

diff --git a/infer/src/checkers/liveness.ml b/infer/src/checkers/liveness.ml
index 7c5171409..4b3180723 100644
--- a/infer/src/checkers/liveness.ml
+++ b/infer/src/checkers/liveness.ml
@@ -64,11 +64,24 @@ let checker {Callbacks.tenv; summary; proc_desc} : Specs.summary =
   let invariant_map =
     Analyzer.exec_cfg cfg (ProcData.make_default proc_desc tenv) ~initial:Domain.empty ~debug:true
   in
+  let procname = Procdesc.get_proc_name proc_desc in
+  let is_cpp_lambda =
+    match Typ.Procname.get_method procname with "operator()" -> true | _ -> false
+  in
+  let is_captured_var pvar =
+    let pvar_name = Pvar.get_name pvar in
+    let pvar_matches (name, _) = Mangled.equal name pvar_name in
+    (* var is captured if the procedure is a lambda and the var is not in the locals or formals *)
+    is_cpp_lambda
+    && not
+         ( List.exists ~f:pvar_matches (Procdesc.get_locals proc_desc)
+         || List.exists ~f:pvar_matches (Procdesc.get_formals proc_desc) )
+  in
   let report_dead_store live_vars = function
     | Sil.Store (Lvar pvar, _, _, loc)
       when not
              ( Pvar.is_frontend_tmp pvar || Pvar.is_return pvar || Pvar.is_global pvar
-             || Domain.mem (Var.of_pvar pvar) live_vars )
+             || Domain.mem (Var.of_pvar pvar) live_vars || is_captured_var pvar )
      -> let issue_id = Localise.to_issue_id Localise.dead_store in
         let message = F.asprintf "The value written to %a is never used" (Pvar.pp Pp.text) pvar in
         let ltr = [Errlog.make_trace_element 0 loc "Write of unused value" []] in
diff --git a/infer/tests/codetoanalyze/cpp/liveness/dead_stores.cpp b/infer/tests/codetoanalyze/cpp/liveness/dead_stores.cpp
index 7c9ee8a3b..1f18d91a4 100644
--- a/infer/tests/codetoanalyze/cpp/liveness/dead_stores.cpp
+++ b/infer/tests/codetoanalyze/cpp/liveness/dead_stores.cpp
@@ -124,6 +124,15 @@ int plus_plus_loop_ok(int n) {
   return i;
 }
 
+void lambda_bad() {
+  int x = []() {
+    int y = 1;
+    y = 2;
+    return y;
+  }();
+  return x;
+}
+
 void capture1_ok() {
   int x = 1;
   [x]() { return x; }();
@@ -133,12 +142,31 @@ void capture2_ok(int x) {
   [x]() { return x; }();
 }
 
-int FP_capture_by_ref_ok() {
+int capture_by_ref1_ok() {
   int x = 0;
   [&x]() { x++; }();
   return x;
 }
 
+int capture_by_ref2_ok() {
+  int x = 0;
+  int y = 0;
+  [&]() {
+    x = x + y;
+    y = x;
+  }();
+  return x + y;
+}
+
+int FN_capture_by_ref_reuseBad() {
+  int x = 0;
+  [&x]() {
+    x = 1; // dead, but we won't report
+    x = 2;
+  }();
+  return x;
+}
+
 void init_capture_ok() {
   [i = 0]() { return i; };
 }
diff --git a/infer/tests/codetoanalyze/cpp/liveness/issues.exp b/infer/tests/codetoanalyze/cpp/liveness/issues.exp
index b88fe2923..980121935 100644
--- a/infer/tests/codetoanalyze/cpp/liveness/issues.exp
+++ b/infer/tests/codetoanalyze/cpp/liveness/issues.exp
@@ -1,8 +1,8 @@
 codetoanalyze/cpp/liveness/dead_stores.cpp, dead_stores::FP_assign_array_tricky_ok, 3, DEAD_STORE, [Write of unused value]
-codetoanalyze/cpp/liveness/dead_stores.cpp, dead_stores::FP_capture_by_ref_ok::lambda_dead_stores.cpp:138:3_operator(), 0, DEAD_STORE, [Write of unused value]
 codetoanalyze/cpp/liveness/dead_stores.cpp, dead_stores::dead_pointer_bad, 2, DEAD_STORE, [Write of unused value]
 codetoanalyze/cpp/liveness/dead_stores.cpp, dead_stores::dead_then_live_bad, 1, DEAD_STORE, [Write of unused value]
 codetoanalyze/cpp/liveness/dead_stores.cpp, dead_stores::easy_bad, 0, DEAD_STORE, [Write of unused value]
+codetoanalyze/cpp/liveness/dead_stores.cpp, dead_stores::lambda_bad::lambda_dead_stores.cpp:128:11_operator(), 1, DEAD_STORE, [Write of unused value]
 codetoanalyze/cpp/liveness/dead_stores.cpp, dead_stores::plus_plus1_bad, 2, DEAD_STORE, [Write of unused value]
 codetoanalyze/cpp/liveness/dead_stores.cpp, dead_stores::plus_plus2_bad, 2, DEAD_STORE, [Write of unused value]
 codetoanalyze/cpp/liveness/dead_stores.cpp, dead_stores::plus_plus3_bad, 2, DEAD_STORE, [Write of unused value]