[pulse] Avoid destructing artificial variables related to coroutine

Summary:
This diff avoids destructing the artificial variables that are related to coroutine, `__promise` and
`__coro_frame`.

https://github.com/llvm/llvm-project/blob/fc6faa1113e9069f41b5500db051210af0eea843/lldb/source/Plugins/LanguageRuntime/CPlusPlus/CPPLanguageRuntime.cpp#L38-L39

Before this diff, they were addressed as if local variables, so that they were nullified/destructed when out of
scope, which introduced false positives of use-after-lifetime.

Reviewed By: ngorogiannis

Differential Revision: D52700500

fbshipit-source-id: 1a941acbae735eaa56c635ccedea6daa56978628

infer/src/IR/Mangled.ml

@@ -41,6 +41,8 @@ let self = from_string "self"
 
 let is_self = function {plain= "self"} -> true | _ -> false
 
+let is_artificial = function {plain= "__promise" | "__coro_frame"} -> true | _ -> false
+
 let return_param = from_string "__return_param"
 
 let is_return_param = function {plain= "__return_param"} -> true | _ -> false

infer/src/IR/Mangled.mli

@@ -39,6 +39,8 @@ val self : t [@@warning "-unused-value-declaration"]
 
 val is_self : t -> bool
 
+val is_artificial : t -> bool
+
 val return_param : t
 
 val is_return_param : t -> bool

infer/src/IR/Pvar.ml

@@ -118,6 +118,8 @@ let is_this pvar = Mangled.is_this (get_name pvar)
 (** Check if a pvar is the special "self" var *)
 let is_self pvar = Mangled.is_self (get_name pvar)
 
+let is_artificial pvar = Mangled.is_artificial (get_name pvar)
+
 (** Check if the pvar is a return var *)
 let is_return pv = Mangled.equal (get_name pv) Ident.name_return
 

infer/src/IR/Pvar.mli

@@ -78,6 +78,9 @@ val is_this : t -> bool
 val is_self : t -> bool
 (** Check if a pvar is the special "self" var *)
 
+val is_artificial : t -> bool
+(** Check if a pvar is an artificial variable related coroutine, "__promise" or "__coro_frame" *)
+
 val is_frontend_tmp : t -> bool
 (** return true if [pvar] is a temporary variable generated by the frontend *)
 

infer/src/IR/Var.ml

@@ -47,6 +47,8 @@ let is_none = function LogicalVar id -> Ident.is_none id | _ -> false
 
 let is_this = function ProgramVar pv -> Pvar.is_this pv | LogicalVar _ -> false
 
+let is_artificial = function ProgramVar pv -> Pvar.is_artificial pv | LogicalVar _ -> false
+
 let get_all_vars_in_exp e =
   let acc = Exp.free_vars e |> Sequence.map ~f:of_id in
   Exp.program_vars e |> Sequence.map ~f:of_pvar |> Sequence.append acc

infer/src/IR/Var.mli

@@ -42,6 +42,8 @@ val is_none : t -> bool
 
 val is_this : t -> bool
 
+val is_artificial : t -> bool
+
 val appears_in_source_code : t -> bool
 (** return true if this variable appears in source code (i.e., is not a LogicalVar or a
     frontend-generated ProgramVar) *)

infer/src/backend/preanal.ml

@@ -381,7 +381,9 @@ module Liveness = struct
     let is_local pvar = not (Liveness.is_always_in_scope proc_desc pvar) in
     let prepend_node_nullify_instructions loc pvars instrs =
       List.fold pvars ~init:instrs ~f:(fun instrs pvar ->
-          if is_local pvar then Sil.Metadata (Nullify (pvar, loc)) :: instrs else instrs )
+          if is_local pvar && not (Pvar.is_artificial pvar) then
+            Sil.Metadata (Nullify (pvar, loc)) :: instrs
+          else instrs )
     in
     let node_deadvars_instruction loc vars =
       let local_vars =
@@ -399,6 +401,7 @@ module Liveness = struct
             let dead_vars, pvars_to_nullify =
               VarDomain.fold
                 (fun var (dead_vars, pvars_to_nullify) ->
+                  let dead_vars = if Var.is_artificial var then dead_vars else var :: dead_vars in
                   let pvars_to_nullify =
                     match Var.get_pvar var with
                     | Some pvar when not (AddressTaken.Domain.mem pvar address_taken_vars) ->
@@ -408,7 +411,7 @@ module Liveness = struct
                     | _ ->
                         pvars_to_nullify
                   in
-                  (var :: dead_vars, pvars_to_nullify) )
+                  (dead_vars, pvars_to_nullify) )
                 to_nullify ([], [])
             in
             let loc = Procdesc.Node.get_last_loc node in

infer/src/pulse/Pulse.ml

@@ -310,7 +310,9 @@ module PulseTransferFunctions = struct
     if flags.cf_injected_destructor then
       match (callee_pname, actuals) with
       | Some (Procname.ObjC_Cpp pname), [(Exp.Lvar pvar, typ)]
-        when Pvar.is_local pvar && not (Procname.ObjC_Cpp.is_inner_destructor pname) ->
+        when Pvar.is_local pvar
+             && (not (Procname.ObjC_Cpp.is_inner_destructor pname))
+             && not (Pvar.is_artificial pvar) ->
           (* ignore inner destructors, only trigger out of scope on the final destructor call *)
           Some (pvar, typ)
       | _ ->

infer/src/pulse/PulseAbductiveDomain.ml

@@ -972,7 +972,7 @@ module Internal = struct
                        else None )
                  in
                  match var with
-                 | Var.ProgramVar pvar ->
+                 | Var.ProgramVar pvar when not (Pvar.is_artificial pvar) ->
                      get_local_typ_opt pvar
                      |> Option.value_map ~default:acc
                           ~f:(add_out_of_scope_attribute addr pvar location history acc)