[deadstore] Do not report on __tmp

Reviewed By: mbouaziz

Differential Revision: D9482603

fbshipit-source-id: 303b74eb4

infer/src/checkers/liveness.ml

@@ -171,8 +171,11 @@ let checker {Callbacks.tenv; summary; proc_desc} : Summary.t =
         false
   in
   let should_report pvar typ live_vars captured_by_ref_vars =
+    (* T32000971: a temporay fix for dead store false positives until we support __unused__ attribute *)
+    let is_unused_tmp_var pvar = String.equal "__tmp" (Pvar.to_string pvar) in
     not
       ( Pvar.is_frontend_tmp pvar || Pvar.is_return pvar || Pvar.is_global pvar
+      || is_unused_tmp_var pvar
       || VarSet.mem (Var.of_pvar pvar) captured_by_ref_vars
       || Domain.mem (Var.of_pvar pvar) live_vars
       || Procdesc.is_captured_var proc_desc pvar

infer/tests/codetoanalyze/cpp/liveness/dead_stores.cpp

@@ -478,4 +478,16 @@ class Exceptions {
 
 void init_in_binop_bad(int x) { x = -x & ~int{0}; }
 
+void FN_unused_tmp_bad() {
+  // T32000971
+  int __tmp = 1;
+}
+
+#define UNUSED(a) __typeof__(&a) __attribute__((unused)) __tmp = &a;
+
+void unused_attribute_ok() {
+  int x;
+  UNUSED(x);
+}
+
 } // namespace dead_stores