+(define-vop (symbol-hash)
+ (:policy :fast-safe)
+ (:translate symbol-hash)
+ (:args (symbol :scs (descriptor-reg)))
+ (:results (res :scs (any-reg)))
+ (:result-types positive-fixnum)
+ (:generator 2
+ ;; The symbol-hash slot of NIL holds NIL because it is also the
+ ;; cdr slot, so we have to strip off the two low bits to make sure
+ ;; it is a fixnum. The lowtag selection magic that is required to
+ ;; ensure this is explained in the comment in objdef.lisp
+ (loadw res symbol symbol-hash-slot other-pointer-lowtag)
+ (inst clrrwi res res (1- n-lowtag-bits))))