;;;; the x86 definitions of some general purpose memory reference VOPs
;;;; inherited by basic memory reference operations

;;;; 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")

(defun symbol-slot-ea (symbol slot &optional (size :qword))
  (make-ea size :disp
           (let ((offset (- (* slot n-word-bytes) other-pointer-lowtag)))
             (if (static-symbol-p symbol)
                 (+ nil-value (static-symbol-offset symbol) offset)
                 (make-fixup symbol :immobile-object offset)))))

(defun gen-cell-set (ea value result)
  (when (sc-is value immediate)
    (let ((bits (encode-value-if-immediate value)))
      (cond ((not result)
             ;; Try to move imm-to-mem if BITS fits
             (acond ((or (and (fixup-p bits)
                              ;; immobile-object fixups must fit in 32 bits
                              (eq (fixup-flavor bits) :immobile-object)
                              bits)
                         (immediate32-p bits))
                     (inst mov ea it))
                    (t
                     (inst mov temp-reg-tn bits)
                     (inst mov ea temp-reg-tn)))
             (return-from gen-cell-set))
            ;; Move the immediate value into RESULT provided that doing so
            ;; doesn't clobber EA. If it would, use TEMP-REG-TN instead.
            ;; TODO: if RESULT is unused, and the immediate fits in an
            ;; imm32 operand, then perform imm-to-mem move, but as the comment
            ;; observes, there's no easy way to spot an unused TN.
            ((or (location= (ea-base ea) result)
                 (awhen (ea-index ea) (location= it result)))
             (inst mov temp-reg-tn bits)
             (setq value temp-reg-tn))
            (t
             ;; Can move into RESULT, then into EA
             (inst mov result bits)
             (inst mov ea result)
             (return-from gen-cell-set)))))
  (inst mov ea value)
  (when result
    ;; Ideally we would skip this move if RESULT is unused hereafter,
    ;; but unfortunately (NOT (TN-READS RESULT)) isn't equivalent
    ;; to there being no reads from the TN at all.
    (move result value)))

;;; CELL-REF and CELL-SET are used to define VOPs like CAR, where the
;;; offset to be read or written is a property of the VOP used.
(define-vop (cell-ref)
  (:args (object :scs (descriptor-reg)))
  (:results (value :scs (descriptor-reg any-reg)))
  (:variant-vars offset lowtag)
  (:policy :fast-safe)
  (:generator 4
    (loadw value object offset lowtag)))
;; This vop's sole purpose is to be an ancestor for other vops, to assign
;; default operands, policy, and generator.
(define-vop (cell-set)
  (:args (object :scs (descriptor-reg))
         (value :scs (descriptor-reg any-reg immediate)))
  (:variant-vars offset lowtag)
  (:policy :fast-safe)
  (:generator 4
    (gen-cell-set (make-ea-for-object-slot object offset lowtag)
                  value nil)))

;;; X86 special
(define-vop (cell-xadd)
  (:args (object :scs (descriptor-reg) :to :result)
         (value :scs (any-reg) :target result))
  (:results (result :scs (any-reg) :from (:argument 1)))
  (:result-types tagged-num)
  (:variant-vars offset lowtag)
  (:policy :fast-safe)
  (:generator 4
    (move result value)
    (inst xadd (make-ea-for-object-slot object offset lowtag) result :lock)))

(define-vop (cell-xsub cell-xadd)
  (:args (object)
         (value :scs (any-reg immediate) :target result))
  (:generator 5
    ;; For constant delta we can avoid a mov followed by neg
    ;; but if 'delta' is most-negative-fixnum, don't negate it.
    ;; Decrementing by most-negative-fixnum is the same as incrementing.
    (sc-case value
     (immediate
      (let ((k (tn-value value)))
        (inst mov result (fixnumize (if (= k most-negative-fixnum) k (- k))))))
     (t
      (move result value)
      (inst neg result)))
    (inst xadd (make-ea-for-object-slot object offset lowtag) result :lock)))

(define-vop (atomic-inc-symbol-global-value cell-xadd)
  (:translate %atomic-inc-symbol-global-value)
  ;; The function which this vop translates will not
  ;; be used unless the variable is proclaimed as fixnum.
  ;; All stores are checked in a safe policy, so this
  ;; vop is safe because it increments a known fixnum.
  (:policy :fast-safe)
  (:arg-types * tagged-num)
  (:variant symbol-value-slot other-pointer-lowtag))

(define-vop (atomic-dec-symbol-global-value cell-xsub)
  (:translate %atomic-dec-symbol-global-value)
  (:policy :fast-safe)
  (:arg-types * tagged-num)
  (:variant symbol-value-slot other-pointer-lowtag))

(macrolet
    ((def-atomic (fun-name inherit slot)
       `(progn
          (define-vop (,(symbolicate fun-name "/FAST") ,inherit)
            (:translate ,fun-name)
            (:policy :fast)
            (:arg-types * tagged-num)
            (:variant ,slot list-pointer-lowtag))
          (define-vop (,(symbolicate fun-name "/SAFE"))
            (:translate ,fun-name)
            (:policy :fast-safe)
            (:args (cell :scs (descriptor-reg))
                   (delta :scs (any-reg immediate)))
            (:results (result :scs (any-reg)))
            (:temporary (:sc descriptor-reg :offset rax-offset) rax)
            (:temporary (:sc any-reg) newval)
            (:arg-types * tagged-num)
            (:result-types tagged-num)
            (:vop-var vop)
            (:generator 10
             (let ((err (generate-error-code vop 'object-not-fixnum-error rax))
                   (const (if (sc-is delta immediate)
                              (fixnumize ,(if (eq inherit 'cell-xsub)
                                              `(let ((x (tn-value delta)))
                                                 (if (= x most-negative-fixnum)
                                                     x (- x)))
                                              `(tn-value delta)))))
                   (retry (gen-label)))
               (loadw rax cell ,slot list-pointer-lowtag)
               (emit-label retry)
               (inst test rax fixnum-tag-mask)
               (inst jmp :nz err)
               (if const
                   (cond ((typep const '(signed-byte 32))
                          (inst lea newval
                                (make-ea :qword :base rax :disp const)))
                         (t
                          (inst mov newval const)
                          (inst add newval rax)))
                   ,(if (eq inherit 'cell-xsub)
                        `(progn (move newval rax)
                                (inst sub newval delta))
                        `(inst lea newval
                               (make-ea :qword :base rax :index delta))))
               (inst cmpxchg
                     (make-ea-for-object-slot cell ,slot list-pointer-lowtag)
                     newval :lock)
               (inst jmp :ne retry)
               (inst mov result rax)))))))
  (def-atomic %atomic-inc-car cell-xadd cons-car-slot)
  (def-atomic %atomic-inc-cdr cell-xadd cons-cdr-slot)
  (def-atomic %atomic-dec-car cell-xsub cons-car-slot)
  (def-atomic %atomic-dec-cdr cell-xsub cons-cdr-slot))
