;;;; predicate VOPs for the x86 VM

;;;; This software is part of the SBCL system. See the README file for
;;;; more information.
;;;;
;;;; This software is derived from the CMU CL system, which was
;;;; written at Carnegie Mellon University and released into the
;;;; public domain. The software is in the public domain and is
;;;; provided with absolutely no warranty. See the COPYING and CREDITS
;;;; files for more information.

(in-package "SB!VM")

;;;; the branch VOP

;;; The unconditional branch, emitted when we can't drop through to the desired
;;; destination. Dest is the continuation we transfer control to.
(define-vop (branch)
  (:info dest)
  (:generator 5
    (inst jmp dest)))


;;;; conditional VOPs

;;; Note: a constant-tn is allowed in CMP; it uses an EA displacement,
;;; not immediate data.
(define-vop (if-eq)
  (:args (x :scs (any-reg descriptor-reg control-stack constant)
            :load-if (not (and (sc-is x immediate)
                               (sc-is y any-reg descriptor-reg
                                      control-stack constant))))
         (y :scs (any-reg descriptor-reg immediate)
            :load-if (not (and (sc-is x any-reg descriptor-reg immediate)
                               (sc-is y control-stack constant)))))
  (:conditional)
  (:info target not-p)
  (:policy :fast-safe)
  (:translate eq)
  (:generator 3
    (let ((x-val (encode-value-if-immediate x))
          (y-val (encode-value-if-immediate y)))
      (cond
        ;; Shorter instruction sequences for these two cases.
        ((and (eql 0 y-val) (sc-is x any-reg descriptor-reg)) (inst test x x))
        ((and (eql 0 x-val) (sc-is y any-reg descriptor-reg)) (inst test y y))

        ;; An encoded value (literal integer) has to be the second argument.
        ((sc-is x immediate) (inst cmp y x-val))

        (t (inst cmp x y-val))))

    (inst jmp (if not-p :ne :e) target)))