;;; -*- Package: ALPHA -*-
;;;
;;; **********************************************************************
;;; This code was written as part of the CMU Common Lisp project at
;;; Carnegie Mellon University, and has been placed in the public domain.
;;;
(ext:file-comment
  "$Header: /project/cmucl/cvsroot/src/compiler/alpha/insts.lisp,v 1.5 2003-03-06 14:13:08 pmai Exp $")
;;;
;;; **********************************************************************
;;;
;;; This file contains the instruction set definition for the Alpha.
;;;
;;; Written by Sean Hallgren.
;;;

(in-package :alpha)

(use-package :new-assem)

(def-assembler-params
  :scheduler-p nil)


;;;; Utility functions.

(defun reg-tn-encoding (tn)
  (declare (type tn tn)
           (values (unsigned-byte 5)))
  (sc-case tn
    (zero zero-offset)
    (null null-offset)
    (t
     (assert (eq (sb-name (sc-sb (tn-sc tn))) 'registers))
     (tn-offset tn))))

(defun fp-reg-tn-encoding (tn)
  (declare (type tn tn))
  (sc-case tn
    (fp-single-zero (tn-offset fp-single-zero-tn))
    (fp-double-zero (tn-offset fp-double-zero-tn))
    (t
     (unless (eq (sb-name (sc-sb (tn-sc tn))) 'float-registers)
       (error "~S isn't a floating-point register." tn))
     (tn-offset tn))))


;;;; Initial disassembler setup.

(disassem:set-disassem-params :instruction-alignment 32)

(defvar *disassem-use-lisp-reg-names* t)

(defparameter reg-symbols
  (map 'vector
       #'(lambda (name)
           (cond ((null name) nil)
                 (t (make-symbol (concatenate 'string "$" name)))))
       *register-names*))

(disassem:define-argument-type reg
  :printer #'(lambda (value stream dstate)
               (declare (stream stream) (fixnum value))
               (let ((regname (aref reg-symbols value)))
                 (princ regname stream)
                 (disassem:maybe-note-associated-storage-ref
                  value
                  'registers
                  regname
                  dstate))))

(defparameter float-reg-symbols
  (coerce
   (loop for n from 0 to 31 collect (make-symbol (format nil "~d" n)))
   'vector))

(disassem:define-argument-type fp-reg
  :printer #'(lambda (value stream dstate)
               (declare (stream stream) (fixnum value))
               (let ((regname (aref float-reg-symbols value)))
                 (princ regname stream)
                 (disassem:maybe-note-associated-storage-ref
                  value
                  'float-registers
                  regname
                  dstate))))

(disassem:define-argument-type relative-label
  :sign-extend t
  :use-label #'(lambda (value dstate)
		 (declare (type (signed-byte 21) value)
			  (type disassem:disassem-state dstate))
		 (+ (ash value 2) (disassem:dstate-cur-addr dstate))))



;;;; Define-instruction-formats for disassembler.
(disassem:define-instruction-format
    (memory 32 :default-printer '(:name :tab ra "," disp "(" rb ")"))
  (op   :field (byte 6 26))
  (ra   :field (byte 5 21) :type 'reg)
  (rb   :field (byte 5 16) :type 'reg)
  (disp :field (byte 16 0) :sign-extend t))

(disassem:define-instruction-format
    (jump 32 :default-printer '(:name :tab ra ",(" rb ")," hint))
  (op    :field (byte 6 26))
  (ra    :field (byte 5 21) :type 'reg)
  (rb    :field (byte 5 16) :type 'reg)
  (subop :field (byte 2 14))
  (hint  :field (byte 14 0)))

(disassem:define-instruction-format
    (branch 32 :default-printer '(:name :tab ra "," disp))
  (op   :field (byte 6 26))
  (ra   :field (byte 5 21) :type 'reg)
  (disp :field (byte 21 0) :type 'relative-label))

(disassem:define-instruction-format
    (reg-operate 32 :default-printer '(:name :tab ra "," rb "," rc))
  (op  :field (byte 6 26))
  (ra  :field (byte 5 21) :type 'reg)
  (rb  :field (byte 5 16) :type 'reg)
  (sbz :field (byte 3 13))
  (f   :field (byte 1 12) :value 0)
  (fn  :field (byte 7 5))
  (rc  :field (byte 5 0) :type 'reg))

(disassem:define-instruction-format
    (lit-operate 32 :default-printer '(:name :tab ra "," lit "," rc))
  (op  :field (byte 6 26))
  (ra  :field (byte 5 21) :type 'reg)
  (lit :field (byte 8 13))
  (f   :field (byte 1 12) :value 1)
  (fn  :field (byte 7 5))
  (rc  :field (byte 5 0) :type 'reg))

(disassem:define-instruction-format
    (fp-operate 32 :default-printer '(:name :tab fa "," fb "," fc))
  (op :field (byte 6 26))
  (fa :field (byte 5 21) :type 'fp-reg)
  (fb :field (byte 5 16) :type 'fp-reg)
  (fn :field (byte 11 5))
  (fc :field (byte 5 0) :type 'fp-reg))

(disassem:define-instruction-format
    (call-pal 32 :default-printer '('call_pal :tab 'pal_ :name))
  (op      :field (byte 6 26) :value 0)
  (palcode :field (byte 26 0)))


;;;; Emitters.
(define-emitter emit-word 16
  (byte 16 0))

(define-emitter emit-lword 32
  (byte 32 0))

(define-emitter emit-qword 64
  (byte 64 0))

(define-emitter emit-memory 32
  (byte 6 26) (byte 5 21) (byte 5 16) (byte 16 0))

(define-emitter emit-branch 32
  (byte 6 26) (byte 5 21) (byte 21 0))

(define-emitter emit-reg-operate 32
  (byte 6 26) (byte 5 21) (byte 5 16) (byte 3 13) (byte 1 12) (byte 7 5)
  (byte 5 0))

(define-emitter emit-lit-operate 32
  (byte 6 26) (byte 5 21) (byte 8 13) (byte 1 12) (byte 7 5) (byte 5 0))

(define-emitter emit-fp-operate 32
  (byte 6 26) (byte 5 21) (byte 5 16) (byte 11 5) (byte 5 0))

(define-emitter emit-pal 32
  (byte 6 26) (byte 26 0))


;;;; Macros for instructions.
(defmacro define-memory (name op &optional fixup float)
  `(define-instruction ,name (segment ra disp rb ,@(if fixup
						       '(&optional type)))
     (:declare (type tn ra rb)
	       ,@(if fixup    ; ### unsigned-byte 16 bad idea?
		     '((type (or (unsigned-byte 16) (signed-byte 16) fixup)
			     disp))
		     '((type (or (unsigned-byte 16) (signed-byte 16)) disp))))
     (:printer memory ((op ,op)))
     (:emitter
      ,@(when fixup
	  `((when (fixup-p disp)
	      (note-fixup segment (or type ,fixup) disp)
	      (setf disp 0))))
      (emit-memory segment ,op ,@(if float
				     '((fp-reg-tn-encoding ra))
				     '((reg-tn-encoding ra)))
		   (reg-tn-encoding rb)
		   disp))))

(defmacro define-jump (name subop)
  `(define-instruction ,name (segment ra rb &optional (hint 0))
     (:declare (type tn ra rb)
	       (type (or (unsigned-byte 14) fixup) hint))
     (:printer jump ((op #x1a) (subop ,subop)))
     (:emitter
      (when (fixup-p hint)
	(note-fixup segment :jmp-hint hint)
	(setf hint 0))
      (emit-memory segment #x1a (reg-tn-encoding ra) (reg-tn-encoding rb)
		   (logior (ash ,subop 14) hint)))))

(defmacro define-branch (name op &optional (float nil))
  `(define-instruction ,name (segment ra target)
     (:declare (type tn ra)
	       (type label target))
     (:printer branch ((op ,op)
		       ,@(when float
			   '((ra nil :type 'fp-reg)))))
     (:emitter
      (emit-back-patch segment 4
		       #'(lambda (segment posn)
			   (emit-branch segment ,op
					,@(if float
					      '((fp-reg-tn-encoding ra))
					      '((reg-tn-encoding ra)))
					(ash (- (label-position target)
						(+ posn 4))
					     -2)))))))

(defmacro define-operate (name op fn)
  `(define-instruction ,name (segment ra rb rc)
     (:declare (type tn ra rc)
	       (type (or tn (unsigned-byte 8)) rb))
     (:printer reg-operate ((op ,op) (fn ,fn)))
     (:printer lit-operate ((op ,op) (fn ,fn)))
     ,@(when (and (= op #x11) (= fn #x20))
	 `((:printer reg-operate ((op ,op) (fn ,fn) (ra 31))
		     '('move :tab rb "," rc))
	   (:printer reg-operate ((op ,op) (fn ,fn) (ra 31) (rb 31) (rc 31))
		     '('nop))))
     (:emitter
      (etypecase rb
	(tn
	 (emit-reg-operate segment ,op (reg-tn-encoding ra)
			   (reg-tn-encoding rb) 0 0 ,fn (reg-tn-encoding rc)))
	(number
	 (emit-lit-operate segment ,op (reg-tn-encoding ra) rb 1 ,fn
		       (reg-tn-encoding rc)))))))

(defmacro define-fp-operate (name op fn &optional (args 3))
  `(define-instruction ,name (segment ,@(when (= args 3) '(fa)) fb fc)
     (:declare (type tn ,@(when (= args 3) '(fa)) fb fc))
     (:printer fp-operate ((op ,op) (fn ,fn) ,@(when (= args 2) '((fa 31))))
	       ,@(when (= args 2)
		   '('(:name :tab fb "," fc))))
     ,@(when (and (= op #x17) (= fn #x20))
	 `((:printer fp-operate ((op ,op) (fn ,fn) (fa 31))
		     '('fabs :tab fb "," fc))))
     (:emitter
      (emit-fp-operate segment ,op ,@(if (= args 3)
					 '((fp-reg-tn-encoding fa))
					 '(31))
		       (fp-reg-tn-encoding fb) ,fn (fp-reg-tn-encoding fc)))))


;;;; Instructions.
(define-memory lda   #x08 :lda)
(define-memory ldah  #x09 :ldah)
(define-memory ldl   #x28)
(define-memory ldq   #x29)
(define-memory ldl_l #x2a)
(define-memory ldq_q #x2b)
(define-memory ldq_u #x0b)
(define-memory stl   #x2c)
(define-memory stq   #x2d)
(define-memory stl_c #x2e)
(define-memory stq_c #x2f)
(define-memory stq_u #x0f)
(define-memory ldf   #x20 nil t)
(define-memory ldg   #x21 nil t)
(define-memory lds   #x22 nil t)
(define-memory ldt   #x23 nil t)
(define-memory stf   #x24 nil t)
(define-memory stg   #x25 nil t)
(define-memory sts   #x26 nil t)
(define-memory stt   #x27 nil t)

(define-jump jmp 0)
(define-jump jsr 1)
(define-jump ret 2)
(define-jump jsr-coroutine 3)

(define-branch br   #x30)
(define-branch bsr  #x34)
(define-branch blbc #x38)
(define-branch blbs #x3c)
(define-branch fbeq #x31 t)
(define-branch fbne #x35 t)
(define-branch beq  #x39)
(define-branch bne  #x3d)
(define-branch fblt #x32 t)
(define-branch fbge #x36 t)
(define-branch blt  #x3a)
(define-branch bge  #x3e)
(define-branch fble #x33 t)
(define-branch fbgt #x37 t)
(define-branch ble  #x3b)
(define-branch bgt  #x3f)

(define-operate addl   #x10 #x00)
(define-operate addl/v #x10 #x40)
(define-operate addq   #x10 #x20)
(define-operate addq/v #x10 #x60)
(define-operate cmpule #x10 #x3d)
(define-operate cmpbge #x10 #x0f)
(define-operate subl   #x10 #x09)
(define-operate subl/v #x10 #x49)
(define-operate subq   #x10 #x29)
(define-operate subq/v #x10 #x69)
(define-operate cmpeq  #x10 #x2d)
(define-operate cmplt  #x10 #x4d)
(define-operate cmple  #x10 #x6d)
(define-operate cmpult #x10 #x1d)
(define-operate s4addl #x10 #x02)
(define-operate s4addq #x10 #x22)
(define-operate s4subl #x10 #x0b)
(define-operate s4subq #x10 #x2b)
(define-operate s8addl #x10 #x12)
(define-operate s8addq #x10 #x32)
(define-operate s8subl #x10 #x1b)
(define-operate s8subq #x10 #x3b)

(define-operate and     #x11 #x00)
(define-operate bic     #x11 #x08)
(define-operate cmoveq  #x11 #x24)
(define-operate cmovne  #x11 #x26)
(define-operate cmovlbs #x11 #x14)
(define-operate bis     #x11 #x20)
(define-operate ornot   #x11 #x28)
(define-operate cmovlt  #x11 #x44)
(define-operate cmovge  #x11 #x46)
(define-operate cmovlbc #x11 #x16)
(define-operate xor     #x11 #x40)
(define-operate eqv     #x11 #x48)
(define-operate cmovle  #x11 #x64)
(define-operate cmovgt  #x11 #x66)

(define-operate sll    #x12 #x39)
(define-operate extbl  #x12 #x06)
(define-operate extwl  #x12 #x16)
(define-operate extll  #x12 #x26)
(define-operate extql  #x12 #x36)
(define-operate extwh  #x12 #x5a)
(define-operate extlh  #x12 #x6a)
(define-operate extqh  #x12 #x7a)
(define-operate sra    #x12 #x3c)
(define-operate insbl  #x12 #x0b)
(define-operate inswl  #x12 #x1b)
(define-operate insll  #x12 #x2b)
(define-operate insql  #x12 #x3b)
(define-operate inswh  #x12 #x57)
(define-operate inslh  #x12 #x67)
(define-operate insqh  #x12 #x77)
(define-operate srl    #x12 #x34)
(define-operate mskbl  #x12 #x02)
(define-operate mskwl  #x12 #x12)
(define-operate mskll  #x12 #x22)
(define-operate mskql  #x12 #x32)
(define-operate mskwh  #x12 #x52)
(define-operate msklh  #x12 #x62)
(define-operate mskqh  #x12 #x72)
(define-operate zap    #x12 #x30)
(define-operate zapnot #x12 #x31)

(define-operate mull   #x13 #x00)
(define-operate mulq/v #x13 #x60)
(define-operate mull/v #x13 #x40)
(define-operate umulh  #x13 #x30)
(define-operate mulq   #x13 #x20)

(define-fp-operate cpys     #x17 #x020)
(define-fp-operate mf_fpcr  #x17 #x025)
(define-fp-operate cpysn    #x17 #x021)
(define-fp-operate mt_fpcr  #x17 #x024)
(define-fp-operate cpyse    #x17 #x022)
(define-fp-operate cvtql/sv #x17 #x530 2)
(define-fp-operate cvtlq    #x17 #x010 2)
(define-fp-operate cvtql    #x17 #x030 2)
(define-fp-operate cvtql/v  #x17 #x130 2)
(define-fp-operate fcmoveq  #x17 #x02a)
(define-fp-operate fcmovne  #x17 #x02b)
(define-fp-operate fcmovlt  #x17 #x02c)
(define-fp-operate fcmovge  #x17 #x02d)
(define-fp-operate fcmovle  #x17 #x02e)
(define-fp-operate fcmovgt  #x17 #x02f)

(define-fp-operate cvtqs #x16 #x0bc 2)
(define-fp-operate cvtqt #x16 #x0be 2)
(define-fp-operate cvtts #x16 #x0ac 2)
(define-fp-operate cvttq #x16 #x0af 2)
(define-fp-operate cvttq/c #x16 #x02f 2)
(define-fp-operate cmpteq #x16 #x5a5)
(define-fp-operate cmptlt #x16 #x5a6)
(define-fp-operate cmptle #x16 #x5a7)
(define-fp-operate cmptun #x16 #x5a4)
(define-fp-operate adds #x16 #x080)
(define-fp-operate addt #x16 #x0a0)
(define-fp-operate divs #x16 #x083)
(define-fp-operate divt #x16 #x0a3)
(define-fp-operate muls #x16 #x082)
(define-fp-operate mult #x16 #x0a2)
(define-fp-operate subs #x16 #x081)
(define-fp-operate subt #x16 #x0a1)

;;; IEEE support
(defconstant +su+   #x500)		; software, underflow enabled
(defconstant +sui+  #x700)		; software, inexact & underflow enabled
(defconstant +sv+   #x500)		; software, interger overflow enabled
(defconstant +svi+  #x700)
(defconstant +rnd+  #x0c0)		; dynamic rounding mode
(defconstant +sud+  #x5c0)
(defconstant +svid+ #x7c0)
(defconstant +suid+ #x7c0)

(define-fp-operate cvtqs_su #x16 (logior +su+ #x0bc) 2)
(define-fp-operate cvtqt_su #x16 (logior +su+ #x0be) 2)
(define-fp-operate cvtts_su #x16 (logior +su+ #x0ac) 2)

(define-fp-operate adds_su #x16 (logior +su+ #x080))
(define-fp-operate addt_su #x16 (logior +su+ #x0a0))
(define-fp-operate divs_su #x16 (logior +su+ #x083))
(define-fp-operate divt_su #x16 (logior +su+ #x0a3))
(define-fp-operate muls_su #x16 (logior +su+ #x082))
(define-fp-operate mult_su #x16 (logior +su+ #x0a2))
(define-fp-operate subs_su #x16 (logior +su+ #x081))
(define-fp-operate subt_su #x16 (logior +su+ #x0a1))

(define-instruction  excb (segment)
  (:emitter (emit-lword segment #x63ff0400)))

(define-instruction trapb (segment)
  (:emitter (emit-lword segment #x63ff0000)))

(define-instruction imb (segment)
  (:emitter (emit-pal segment 0 #x000086)))

(define-instruction gentrap (segment code)
  (:printer call-pal ((palcode #xaa0000)))
  (:emitter
	 ; BAU: This *might* cause troubles on Alphas that only have ARC firmware,
	 ; as the Alpha Architecture Handbook lists the bugchk PALcode instruction
	 ; only for the OpenVMS/Digital UNIX PALcode (SRM firmware), but not for
	 ; the Windows NT PALcode (ARC firmware) (see p. C-19 in the AAH,
	 ; opcode 00.0081)
	 ; Oddly enough, even though the gentrap instruction is defined for all
	 ; three PALcode instruction sets, Eric Marsden noticed that it was not
	 ; working as expected under some PALcode setups.
   (emit-pal segment 0 #x000081)      ; actually bugchk PALcode instruction
   ;; (emit-pal segment 0 #x0000aa)   ; gentrap PALcode instruction
   (emit-lword segment code)))

(define-instruction-macro move (src dst)
  `(inst bis zero-tn ,src ,dst))

(define-instruction-macro not (src dst)
  `(inst ornot zero-tn ,src ,dst))

(define-instruction-macro fmove (src dst)
  `(inst cpys ,src ,src ,dst))

(define-instruction-macro fabs (src dst)
  `(inst cpys fp-single-zero-tn ,src ,dst))

(define-instruction-macro fneg (src dst)
  `(inst cpysn ,src ,src ,dst))

(define-instruction-macro nop ()
  `(inst bis zero-tn zero-tn zero-tn))

(defun %li (value reg)
  (etypecase value
    ((signed-byte 16)
     (inst lda reg value zero-tn))
    ((signed-byte 32)
     (flet ((se (x n)
	      (let ((x (logand x (lognot (ash -1 n)))))
		(if (logbitp (1- n) x)
		    (logior (ash -1 (1- n)) x)
		    x))))
       (let* ((value (se value 32))
	      (low (ldb (byte 16 0) value))
	      (tmp1 (- value (se low 16)))
	      (high (ldb (byte 16 16) tmp1))
	      (tmp2 (- tmp1 (se (ash high 16) 32)))
	      (extra 0))
	 (unless (= tmp2 0)
	   (setf extra #x4000)
	   (setf tmp1 (- tmp1 #x40000000))
	   (setf high (ldb (byte 16 16) tmp1)))
	 (inst lda reg low zero-tn)
	 (unless (= extra 0)
	   (inst ldah reg extra reg))
	 (unless (= high 0)
	   (inst ldah reg high reg)))))
    ((or (unsigned-byte 32) (signed-byte 64) (unsigned-byte 64))
     (let* ((value1 (if (logbitp 15 value) (+ value (ash 1 16)) value))
	    (value2 (if (logbitp 31 value) (+ value (ash 1 32)) value1))
	    (value3 (if (logbitp 47 value) (+ value (ash 1 48)) value2)))
       (inst lda reg (ldb (byte 16 32) value2) zero-tn)
       (unless (= value3 0)
	 (inst ldah reg (ldb (byte 16 48) value3) reg))
       (unless (and (= value2 0) (= value3 0))
	 (inst sll reg 32 reg))
       (unless (= value 0)
	 (inst lda reg (ldb (byte 16 0) value) reg))
       (unless (= value1 0)
	 (inst ldah reg (ldb (byte 16 16) value1) reg))))
    (fixup
     (inst lda reg value zero-tn :bits-47-32)
     (inst ldah reg value reg :bits-63-48)
     (inst sll reg 32 reg)
     (inst lda reg value reg)
     (inst ldah reg value reg))))
  
(define-instruction-macro li (value reg)
  `(%li ,value ,reg))


;;;;

(define-instruction lword (segment lword)
  (:declare (type (or (unsigned-byte 32) (signed-byte 32)) lword))
  (:cost 0)
  (:emitter
   (emit-lword segment lword)))

(define-instruction short (segment word)
  (:declare (type (or (unsigned-byte 16) (signed-byte 16)) word))
  (:cost 0)
  (:emitter
   (emit-word segment word)))

(define-instruction byte (segment byte)
  (:declare (type (or (unsigned-byte 8) (signed-byte 8)) byte))
  (:cost 0)
  (:emitter
   (emit-byte segment byte)))

(defun emit-header-data (segment type)
  (emit-back-patch
   segment 4
   #'(lambda (segment posn)
       (emit-lword segment
		  (logior type
			  (ash (+ posn (component-header-length))
			       (- type-bits word-shift)))))))

(define-instruction function-header-word (segment)
  (:cost 0)
  (:emitter
   (emit-header-data segment function-header-type)))

(define-instruction lra-header-word (segment)
  (:cost 0)
  (:emitter
   (emit-header-data segment return-pc-header-type)))

(defun emit-compute-inst (segment vop dst src label temp calc)
  (declare (ignore temp))
  (emit-chooser
   ;; We emit either 12 or 4 bytes, so we maintain 8 byte alignments.
   segment 12 3
   #'(lambda (segment posn delta-if-after)
       (let ((delta (funcall calc label posn delta-if-after)))
	  (when (<= (- (ash 1 15)) delta (1- (ash 1 15)))
	    (emit-back-patch segment 4
			     #'(lambda (segment posn)
				 (assemble (segment vop)
					   (inst lda dst
						 (funcall calc label posn 0)
						 src))))
	    t)))
   #'(lambda (segment posn)
       (assemble (segment vop)
	 (flet ((se (x n)
		  (let ((x (logand x (lognot (ash -1 n)))))
		    (if (logbitp (1- n) x)
			(logior (ash -1 (1- n)) x)
			x))))
	   (let* ((value (se (funcall calc label posn 0) 32))
		  (low (ldb (byte 16 0) value))
		  (tmp1 (- value (se low 16)))
		  (high (ldb (byte 16 16) tmp1))
		  (tmp2 (- tmp1 (se (ash high 16) 32)))
		  (extra 0))
	     (unless (= tmp2 0)
	       (setf extra #x4000)
	       (setf tmp1 (- tmp1 #x40000000))
	       (setf high (ldb (byte 16 16) tmp1)))
	     (inst lda dst low src)
	     (inst ldah dst extra dst)
	     (inst ldah dst high dst)))))))

;; code = fn - header - label-offset + other-pointer-tag
(define-instruction compute-code-from-fn (segment dst src label temp)
  (:declare (type tn dst src temp) (type label label))
  (:vop-var vop)
  (:emitter
   (emit-compute-inst segment vop dst src label temp
		      #'(lambda (label posn delta-if-after)
			  (- other-pointer-type
			     (label-position label posn delta-if-after)
			     (component-header-length))))))

;; code = lra - other-pointer-tag - header - label-offset + other-pointer-tag
;;      = lra - (header + label-offset)
(define-instruction compute-code-from-lra (segment dst src label temp)
  (:declare (type tn dst src temp) (type label label))
  (:vop-var vop)
  (:emitter
   (emit-compute-inst segment vop dst src label temp
		      #'(lambda (label posn delta-if-after)
			  (- (+ (label-position label posn delta-if-after)
				(component-header-length)))))))

;; lra = code + other-pointer-tag + header + label-offset - other-pointer-tag
(define-instruction compute-lra-from-code (segment dst src label temp)
  (:declare (type tn dst src temp) (type label label))
  (:vop-var vop)
  (:emitter
   (emit-compute-inst segment vop dst src label temp
		      #'(lambda (label posn delta-if-after)
			  (+ (label-position label posn delta-if-after)
			     (component-header-length))))))
