[hil] don't crash on deref of magic address

Summary: In HIL, allow deref'ing a magic address like `0xdeadbeef` for debugging purposes. Previously, we would crash on code like this.

Reviewed By: mbouaziz

Differential Revision: D6143802

fbshipit-source-id: 4151924

infer/src/IR/HilInstr.ml

@@ -89,6 +89,13 @@ let of_sil ~include_array_indexes ~f_resolve_id (instr: Sil.instr) =
                 L.(die InternalError)
                   "Invalid pointer arithmetic expression %a used as LHS at %a" Exp.pp lhs_exp
                   Location.pp_file_pos loc )
+        | Constant Const.Cint i ->
+            (* this can happen in intentionally crashing code like *0xdeadbeef = 0 used for
+               debugging. doesn't really matter what we do here, so just create a dummy var *)
+            let dummy_base_var =
+              Var.of_id (Ident.create_normal (Ident.string_to_name (IntLit.to_string i)) 0)
+            in
+            ((dummy_base_var, Typ.void_star), [])
         | _ ->
             L.(die InternalError)
               "Non-assignable LHS expression %a at %a" Exp.pp lhs_exp Location.pp_file_pos loc

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

@@ -137,3 +137,6 @@ int ok6() {
   x = 7;
   return x;
 }
+
+// this crashes HIL if we're not careful
+void deref_magic_addr_ok() { *(int*)0xdeadbeef = 0; }