[sledge] Interpret conversions between float types as identity

Summary:
Since floats of any width are interpreted the same (as exact rationals
where possible and uninterpreted constants otherwise), this does not
introduce additional infidelity.

Reviewed By: da319

Differential Revision: D24746225

fbshipit-source-id: bc8e7bdb9

sledge/src/llair_to_Fol.ml

@@ -87,6 +87,7 @@ and term : Llair.Exp.t -> T.t =
         | _ -> uap1 (Unsigned bits) a
       else uap1 (Unsigned bits) a
   | Ap1 (Convert {src= Pointer _}, Pointer _, e) -> term e
+  | Ap1 (Convert {src= Float _}, Float _, e) -> term e
   | Ap1 (Convert {src}, dst, e) ->
       let s =
         Format.asprintf "convert_%a_of_%a" Llair.Typ.pp dst Llair.Typ.pp src