[frontend] Record attribute unused in local variable data

Summary: To avoid dead store false positives we skip initialization of a variable that has an `unused` attribute. However, this causes uninitialized value false positives when the variable is later used in macros. To fix this, instead of skipping initialization we record the information about `unused` attribute in local variable data that we can later use for filtering out dead store issues.

Reviewed By: jvillard

Differential Revision: D22868050

fbshipit-source-id: 4a2d0e680

infer/src/IR/ProcAttributes.ml

@@ -29,12 +29,13 @@ let pp_objc_accessor_type fmt objc_accessor_type =
     annots
 
 
-type var_data = {name: Mangled.t; typ: Typ.t; modify_in_block: bool; is_constexpr: bool}
+type var_data =
+  {name: Mangled.t; typ: Typ.t; modify_in_block: bool; is_constexpr: bool; is_declared_unused: bool}
 [@@deriving compare]
 
-let pp_var_data fmt {name; typ; modify_in_block} =
+let pp_var_data fmt {name; typ; modify_in_block; is_declared_unused} =
-  F.fprintf fmt "@[<h>{ name=@ %a;@ typ=@ %a;@ modify_in_block=@ %b@ }@]" Mangled.pp name
+  F.fprintf fmt "@[<h>{ name=@ %a;@ typ=@ %a;@ modify_in_block=@ %b;@ is_declared_unused=@ %b@ }@]"
-    (Typ.pp_full Pp.text) typ modify_in_block
+    Mangled.pp name (Typ.pp_full Pp.text) typ modify_in_block is_declared_unused
 
 
 type t =

infer/src/IR/ProcAttributes.mli

@@ -17,7 +17,8 @@ type var_data =
   ; modify_in_block: bool
         (** __block attribute of Objective-C variables, means that it will be modified inside a
             block *)
-  ; is_constexpr: bool }
+  ; is_constexpr: bool
+  ; is_declared_unused: bool  (** variable declared with attribute [unused] *) }
 
 type t =
   { access: PredSymb.access  (** visibility access *)

infer/src/checkers/liveness.ml

@@ -236,14 +236,16 @@ let checker {IntraproceduralAnalysis.proc_desc; err_log} =
         false
   in
   let locals = Procdesc.get_locals proc_desc in
-  let is_constexpr pvar =
+  let is_constexpr_or_unused pvar =
     List.find locals ~f:(fun local_data ->
         Mangled.equal (Pvar.get_name pvar) local_data.ProcAttributes.name )
-    |> Option.exists ~f:(fun local -> local.ProcAttributes.is_constexpr)
+    |> Option.exists ~f:(fun local ->
+           local.ProcAttributes.is_constexpr || local.ProcAttributes.is_declared_unused )
   in
   let should_report pvar typ live_vars captured_by_ref_vars =
     not
-      ( Pvar.is_frontend_tmp pvar || Pvar.is_return pvar || Pvar.is_global pvar || is_constexpr pvar
+      ( Pvar.is_frontend_tmp pvar || Pvar.is_return pvar || Pvar.is_global pvar
+      || is_constexpr_or_unused pvar
       || VarSet.mem (Var.of_pvar pvar) captured_by_ref_vars
       || Domain.mem (Var.of_pvar pvar) live_vars
       || Procdesc.is_captured_pvar proc_desc pvar

infer/src/clang/cTrans.ml

@@ -205,7 +205,12 @@ module CTrans_funct (F : CModule_type.CFrontend) : CModule_type.CTranslation = s
       CVar_decl.mk_temp_sil_var_for_expr context ~name:var_name ~clang_pointer expr_info
     in
     let var_data =
-      ProcAttributes.{name= Pvar.get_name pvar; typ; modify_in_block= false; is_constexpr= false}
+      ProcAttributes.
+        { name= Pvar.get_name pvar
+        ; typ
+        ; modify_in_block= false
+        ; is_constexpr= false
+        ; is_declared_unused= false }
     in
     Procdesc.append_locals procdesc [var_data] ;
     (Exp.Lvar pvar, typ)
@@ -245,7 +250,8 @@ module CTrans_funct (F : CModule_type.CFrontend) : CModule_type.CTranslation = s
                 { name= Pvar.get_name pvar
                 ; typ= return_type
                 ; modify_in_block= false
-                ; is_constexpr= false }
+                ; is_constexpr= false
+                ; is_declared_unused= false }
               in
               Procdesc.append_locals procdesc [var_data] ;
               Exp.Lvar pvar
@@ -1201,7 +1207,11 @@ module CTrans_funct (F : CModule_type.CFrontend) : CModule_type.CTranslation = s
           let pvar = Pvar.mk_tmp "__temp_construct_" (Procdesc.get_proc_name procdesc) in
           let class_type = CType_decl.get_type_from_expr_info ei context.CContext.tenv in
           let var_data : ProcAttributes.var_data =
-            {name= Pvar.get_name pvar; typ= class_type; modify_in_block= false; is_constexpr= false}
+            { name= Pvar.get_name pvar
+            ; typ= class_type
+            ; modify_in_block= false
+            ; is_constexpr= false
+            ; is_declared_unused= false }
           in
           Procdesc.append_locals procdesc [var_data] ;
           (Exp.Lvar pvar, class_type)
@@ -1615,7 +1625,11 @@ module CTrans_funct (F : CModule_type.CFrontend) : CModule_type.CTranslation = s
         let pvar = CVar_decl.mk_temp_sil_var procdesc ~name:"SIL_temp_conditional___" in
         let var_data =
           ProcAttributes.
-            {name= Pvar.get_name pvar; typ= var_typ; modify_in_block= false; is_constexpr= false}
+            { name= Pvar.get_name pvar
+            ; typ= var_typ
+            ; modify_in_block= false
+            ; is_constexpr= false
+            ; is_declared_unused= false }
         in
         Procdesc.append_locals procdesc [var_data] ;
         let continuation' = mk_cond_continuation trans_state.continuation in
@@ -2435,8 +2449,8 @@ module CTrans_funct (F : CModule_type.CFrontend) : CModule_type.CTranslation = s
     |> mk_trans_result ret_exp_typ
 
 
-  and init_expr_trans ?(is_var_unused = false) ?(is_initListExpr_builtin = false) trans_state
+  and init_expr_trans ?(is_initListExpr_builtin = false) trans_state var_exp_typ ?qual_type
-      var_exp_typ ?qual_type var_stmt_info init_expr_opt =
+      var_stmt_info init_expr_opt =
     match init_expr_opt with
     | None -> (
       match Option.bind qual_type ~f:(fun qt -> CAst_utils.get_type qt.Clang_ast_t.qt_type_ptr) with
@@ -2464,8 +2478,7 @@ module CTrans_funct (F : CModule_type.CFrontend) : CModule_type.CTranslation = s
         in
         let assign_trans_control_opt =
           if
-            is_var_unused
+            (* variable might be initialized already - do nothing in that case*)
-            || (* variable might be initialized already - do nothing in that case*)
             List.exists ~f:(Exp.equal var_exp) res_trans_ie.control.initd_exps
           then None
           else
@@ -2501,21 +2514,18 @@ module CTrans_funct (F : CModule_type.CFrontend) : CModule_type.CTranslation = s
     let context = trans_state.context in
     let procdesc = context.CContext.procdesc in
     let procname = Procdesc.get_proc_name procdesc in
-    let do_var_dec ~is_var_unused var_decl qual_type vdi next_node =
+    let do_var_dec var_decl qual_type vdi next_node =
       let pvar = CVar_decl.sil_var_of_decl context var_decl procname in
       let typ = CType_decl.qual_type_to_sil_type context.CContext.tenv qual_type in
       CVar_decl.add_var_to_locals procdesc var_decl typ pvar ;
       let trans_state' = {trans_state with succ_nodes= next_node} in
-      init_expr_trans ~is_var_unused trans_state' (Exp.Lvar pvar, typ) ~qual_type stmt_info
+      init_expr_trans trans_state' (Exp.Lvar pvar, typ) ~qual_type stmt_info
         vdi.Clang_ast_t.vdi_init_expr
     in
-    let has_unused_attr attributes =
-      List.exists attributes ~f:(function `UnusedAttr _ -> true | _ -> false)
-    in
     let rec aux : decl list -> trans_result option = function
       | [] ->
           None
-      | (VarDecl ({di_attributes}, _, qt, vdi) as var_decl) :: var_decls' ->
+      | (VarDecl (_, _, qt, vdi) as var_decl) :: var_decls' ->
           (* Var are defined when procdesc is created, here we only take care of initialization *)
           let res_trans_tl = aux var_decls' in
           let root_nodes_tl, instrs_tl, initd_exps_tl =
@@ -2525,8 +2535,7 @@ module CTrans_funct (F : CModule_type.CFrontend) : CModule_type.CTranslation = s
             | Some {control= {root_nodes; instrs; initd_exps}} ->
                 (root_nodes, instrs, initd_exps)
           in
-          let is_var_unused = has_unused_attr di_attributes in
+          let res_trans_tmp = do_var_dec var_decl qt vdi root_nodes_tl in
-          let res_trans_tmp = do_var_dec ~is_var_unused var_decl qt vdi root_nodes_tl in
           (* keep the last return and leaf_nodes from the list *)
           let return, leaf_nodes =
             match res_trans_tl with
@@ -2895,7 +2904,8 @@ module CTrans_funct (F : CModule_type.CFrontend) : CModule_type.CTranslation = s
       [ { ProcAttributes.name= Pvar.get_name temp
         ; typ= array_typ
         ; modify_in_block= false
-        ; is_constexpr= false } ] ;
+        ; is_constexpr= false
+        ; is_declared_unused= false } ] ;
     (* 2. Translate array elements *)
     let res_trans_elems = List.mapi ~f:(exec_instruction_with_trans_state trans_state None) stmts in
     (* 3. Add array initialization (elements assignments) *)
@@ -3240,7 +3250,12 @@ module CTrans_funct (F : CModule_type.CFrontend) : CModule_type.CTranslation = s
     let res_trans = init_expr_trans trans_state var_exp_typ stmt_info (Some temp_exp) in
     let _, typ = res_trans.return in
     let var_data =
-      ProcAttributes.{name= Pvar.get_name pvar; typ; modify_in_block= false; is_constexpr= false}
+      ProcAttributes.
+        { name= Pvar.get_name pvar
+        ; typ
+        ; modify_in_block= false
+        ; is_constexpr= false
+        ; is_declared_unused= false }
     in
     Procdesc.append_locals procdesc [var_data] ;
     res_trans

infer/src/clang/cVar_decl.ml

@@ -70,8 +70,11 @@ let add_var_to_locals procdesc var_decl typ pvar =
           vdi.Clang_ast_t.vdi_is_const_expr
           || (Typ.is_const typ.Typ.quals && vdi.Clang_ast_t.vdi_is_init_expr_cxx11_constant)
         in
+        let is_declared_unused =
+          List.exists decl_info.di_attributes ~f:(function `UnusedAttr _ -> true | _ -> false)
+        in
         let var_data : ProcAttributes.var_data =
-          {name= Pvar.get_name pvar; typ; modify_in_block; is_constexpr}
+          {name= Pvar.get_name pvar; typ; modify_in_block; is_constexpr; is_declared_unused}
         in
         Procdesc.append_locals procdesc [var_data]
   | _ ->

infer/src/java/jTrans.ml

@@ -437,7 +437,8 @@ let create_cm_procdesc source_file program icfg cm proc_name =
     let locals_ = translate_locals program tenv formals bytecode jbir_code in
     let locals =
       List.map locals_ ~f:(fun (name, typ) ->
-          ({name; typ; modify_in_block= false; is_constexpr= false} : ProcAttributes.var_data) )
+          ( {name; typ; modify_in_block= false; is_constexpr= false; is_declared_unused= false}
+            : ProcAttributes.var_data ) )
     in
     let method_annotation = JAnnotation.translate_method cm.Javalib.cm_annotations in
     let proc_attributes =

infer/tests/codetoanalyze/cpp/uninit/uninit.cpp

@@ -344,3 +344,8 @@ void use_uninit_in_expr_bad() {
   int x;
   int y = x + 2;
 }
+
+int unused_attribute_ok() {
+  int __attribute__((unused)) x = 42;
+  return x;
+}

infer/tests/codetoanalyze/objc/shared/field_superclass/SuperExample.m.dot

@@ -7,7 +7,7 @@ digraph cfg {
 "super_example_main.e3ebe95e6c5ae811733f235c29fbbf6d_2" [label="2: Exit super_example_main \n  " color=yellow style=filled]
 	
 
-"super_example_main.e3ebe95e6c5ae811733f235c29fbbf6d_3" [label="3:  DeclStmt \n   VARIABLE_DECLARED(a:objc_object*); [line 40, column 5]\n  n$0=_fun___objc_alloc_no_fail(sizeof(t=ASuper):unsigned long) [line 40, column 21]\n  n$1=_fun_NSObject.init(n$0:ASuper*) virtual [line 40, column 21]\n " shape="box"]
+"super_example_main.e3ebe95e6c5ae811733f235c29fbbf6d_3" [label="3:  DeclStmt \n   VARIABLE_DECLARED(a:objc_object*); [line 40, column 5]\n  n$0=_fun___objc_alloc_no_fail(sizeof(t=ASuper):unsigned long) [line 40, column 21]\n  n$1=_fun_NSObject.init(n$0:ASuper*) virtual [line 40, column 21]\n  *&a:objc_object*=n$1 [line 40, column 5]\n " shape="box"]
 	
 
 	 "super_example_main.e3ebe95e6c5ae811733f235c29fbbf6d_3" -> "super_example_main.e3ebe95e6c5ae811733f235c29fbbf6d_2" ;