[infer][backend] Only call the prover to check that an expression being dereferenced is not null after checking if the expression is associated with @Nullable

Summary: I tested on Fresco and this reduced the number of calls to Prover.check_disequal by 30%.

Reviewed By: cristianoc

Differential Revision: D5237774

fbshipit-source-id: 377545e

infer/src/backend/rearrange.ml

@@ -1368,8 +1368,9 @@ let check_dereference_error tenv pdesc (prop : Prop.normal Prop.t) lexp loc =
   let is_deref_of_nullable =
     let is_definitely_non_null exp prop =
       Prover.check_disequal tenv prop exp Exp.zero in
-    Config.report_nullable_inconsistency && not (is_definitely_non_null root prop)
-    && Option.is_some nullable_var_opt in
+    Config.report_nullable_inconsistency
+    && Option.is_some nullable_var_opt
+    && not (is_definitely_non_null root prop) in
   let relevant_attributes_getters = [
     Attribute.get_resource tenv;
     Attribute.get_undef tenv;