From 63545b1e648be29ddbe6973f3a57184c59016854 Mon Sep 17 00:00:00 2001
From: Sungkeun Cho <scho@fb.com>
Date: Tue, 26 Jan 2021 03:19:29 -0800
Subject: [PATCH] [liveness] Fix liveness analysis not to kill constructor
 targets

Summary:
In the previous live analysis, it handled class constructor targets as
dead before its calling.  For example,

```
// BEFORE live variables {src}
A::A(&tgt, &src)
// AFTER live variables {tgt, src}
```

It *may* be correct if we says the field values written in `tgt` is
dead.  However, we cannot says the location of `tgt` is dead.

Because of this bug,

```
A x = y;
```

was translated to

```
VARIABLE_DECLARED(x)
EXIT_SCOPE(x)

// x was dead here
A::A(&x, &y)
```

See that `EXIT_SCOPE(x)` is added right after its declaration, since
the liveness analysis said `x` was dead there.

Reviewed By: ezgicicek

Differential Revision: D26048344

fbshipit-source-id: a172994e2
---
 infer/src/checkers/liveness.ml | 19 +++----------------
 1 file changed, 3 insertions(+), 16 deletions(-)

diff --git a/infer/src/checkers/liveness.ml b/infer/src/checkers/liveness.ml
index 103528439..af5a8f9e1 100644
--- a/infer/src/checkers/liveness.ml
+++ b/infer/src/checkers/liveness.ml
@@ -107,21 +107,9 @@ module TransferFunctions (LConfig : LivenessConfig) (CFG : ProcCfg.S) = struct
            Domain.add (Var.of_pvar pvar) astate_acc )
 
 
-  let add_live_actuals actuals call_exp live_acc =
-    let add_live_actuals_ exps acc =
-      List.fold exps ~f:(fun acc_ exp -> exp_add_live exp acc_) ~init:acc
-    in
+  let add_live_actuals actuals live_acc =
     let actuals = List.map actuals ~f:(fun (e, _) -> Exp.ignore_cast e) in
-    match Exp.ignore_cast call_exp with
-    | Exp.Const (Cfun (Procname.ObjC_Cpp _ as pname)) when Procname.is_constructor pname -> (
-      (* first actual passed to a C++ constructor is actually written, not read *)
-      match actuals with
-      | Exp.Lvar pvar :: exps ->
-          Domain.remove (Var.of_pvar pvar) live_acc |> add_live_actuals_ exps
-      | exps ->
-          add_live_actuals_ exps live_acc )
-    | _ ->
-        add_live_actuals_ actuals live_acc
+    List.fold actuals ~f:(fun acc_ exp -> exp_add_live exp acc_) ~init:live_acc
 
 
   let exec_instr astate proc_desc _ = function
@@ -156,8 +144,7 @@ module TransferFunctions (LConfig : LivenessConfig) (CFG : ProcCfg.S) = struct
           else (actuals, astate)
         in
         Domain.remove (Var.of_id ret_id) astate
-        |> exp_add_live call_exp
-        |> add_live_actuals actuals_to_read call_exp
+        |> exp_add_live call_exp |> add_live_actuals actuals_to_read
     | Sil.Metadata _ ->
         astate