[sledge] Improve simplification of negated booleans

Reviewed By: mbouaziz

Differential Revision: D12854516

fbshipit-source-id: e6d454a21

sledge/src/llair/exp.ml

@@ -839,6 +839,8 @@ let rec simp_not (typ : Typ.t) exp =
   | ( App {op= App {op= App {op= Conditional; arg= cnd}; arg= thn}; arg= els}
     , Integer {bits= 1} ) ->
       simp_cond cnd (simp_not typ thn) (simp_not typ els)
+  (* ¬false ==> true ¬true ==> false *)
+  | Integer {data}, Integer {bits= 1} -> bool (Z.is_false data)
   (* ¬b ==> false = b *)
   | b, Integer {bits= 1} -> App {op= App {op= Eq; arg= bool false}; arg= b}
   (* ¬e ==> true xor e *)

sledge/src/llair/exp_test.ml

@@ -178,7 +178,7 @@ let%test_module _ =
 
     let%expect_test _ =
       pf (z != z) ;
-      [%expect {| (0 = -1) |}]
+      [%expect {| 0 |}]
 
     let%expect_test _ =
       pf (!1 = !0) ;