[sbcl.git] / src / compiler / x86-64 / call.lisp

;;;; function call 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")
\f
;;;; interfaces to IR2 conversion

;;; Return a wired TN describing the N'th full call argument passing
;;; location.
(!def-vm-support-routine standard-arg-location (n)
  (declare (type unsigned-byte n))
  (if (< n register-arg-count)
      (make-wired-tn *backend-t-primitive-type* descriptor-reg-sc-number
                     (nth n *register-arg-offsets*))
      (make-wired-tn *backend-t-primitive-type* control-stack-sc-number n)))

;;; Make a passing location TN for a local call return PC.
;;;
;;; Always wire the return PC location to the stack in its standard
;;; location.
(!def-vm-support-routine make-return-pc-passing-location (standard)
  (declare (ignore standard))
  (make-wired-tn (primitive-type-or-lose 'system-area-pointer)
                 sap-stack-sc-number return-pc-save-offset))

;;; This is similar to MAKE-RETURN-PC-PASSING-LOCATION, but makes a
;;; location to pass OLD-FP in.
;;;
;;; This is wired in both the standard and the local-call conventions,
;;; because we want to be able to assume it's always there. Besides,
;;; the x86 doesn't have enough registers to really make it profitable
;;; to pass it in a register.
(!def-vm-support-routine make-old-fp-passing-location (standard)
  (declare (ignore standard))
  (make-wired-tn *fixnum-primitive-type* control-stack-sc-number
                 ocfp-save-offset))

;;; Make the TNs used to hold OLD-FP and RETURN-PC within the current
;;; function. We treat these specially so that the debugger can find
;;; them at a known location.
;;;
;;; Without using a save-tn - which does not make much sense if it is
;;; wired to the stack?
(!def-vm-support-routine make-old-fp-save-location (physenv)
  (physenv-debug-live-tn (make-wired-tn *fixnum-primitive-type*
                                        control-stack-sc-number
                                        ocfp-save-offset)
                         physenv))
(!def-vm-support-routine make-return-pc-save-location (physenv)
  (physenv-debug-live-tn
   (make-wired-tn (primitive-type-or-lose 'system-area-pointer)
                  sap-stack-sc-number return-pc-save-offset)
   physenv))

;;; Make a TN for the standard argument count passing location. We only
;;; need to make the standard location, since a count is never passed when we
;;; are using non-standard conventions.
(!def-vm-support-routine make-arg-count-location ()
  (make-wired-tn *fixnum-primitive-type* any-reg-sc-number rcx-offset))

;;; Make a TN to hold the number-stack frame pointer. This is allocated
;;; once per component, and is component-live.
(!def-vm-support-routine make-nfp-tn ()
  (make-restricted-tn *fixnum-primitive-type* ignore-me-sc-number))

(!def-vm-support-routine make-stack-pointer-tn ()
  (make-normal-tn *fixnum-primitive-type*))

(!def-vm-support-routine make-number-stack-pointer-tn ()
  (make-restricted-tn *fixnum-primitive-type* ignore-me-sc-number))

;;; Return a list of TNs that can be used to represent an unknown-values
;;; continuation within a function.
(!def-vm-support-routine make-unknown-values-locations ()
  (list (make-stack-pointer-tn)
        (make-normal-tn *fixnum-primitive-type*)))

;;; This function is called by the ENTRY-ANALYZE phase, allowing
;;; VM-dependent initialization of the IR2-COMPONENT structure. We
;;; push placeholder entries in the CONSTANTS to leave room for
;;; additional noise in the code object header.
(!def-vm-support-routine select-component-format (component)
  (declare (type component component))
  ;; The 1+ here is because for the x86 the first constant is a
  ;; pointer to a list of fixups, or NIL if the code object has none.
  ;; (If I understand correctly, the fixups are needed at GC copy
  ;; time because the X86 code isn't relocatable.)
  ;;
  ;; KLUDGE: It'd be cleaner to have the fixups entry be a named
  ;; element of the CODE (aka component) primitive object. However,
  ;; it's currently a large, tricky, error-prone chore to change
  ;; the layout of any primitive object, so for the foreseeable future
  ;; we'll just live with this ugliness. -- WHN 2002-01-02
  (dotimes (i (1+ code-constants-offset))
    (vector-push-extend nil
                        (ir2-component-constants (component-info component))))
  (values))
\f
;;;; frame hackery

;;; This is used for setting up the Old-FP in local call.
(define-vop (current-fp)
  (:results (val :scs (any-reg control-stack)))
  (:generator 1
    (move val rbp-tn)))

;;; We don't have a separate NFP, so we don't need to do anything here.
(define-vop (compute-old-nfp)
  (:results (val))
  (:ignore val)
  (:generator 1
    nil))

(define-vop (xep-allocate-frame)
  (:info start-lab copy-more-arg-follows)
  (:vop-var vop)
  (:generator 1
    (emit-alignment n-lowtag-bits)
    (trace-table-entry trace-table-fun-prologue)
    (emit-label start-lab)
    ;; Skip space for the function header.
    (inst simple-fun-header-word)
    (dotimes (i (* n-word-bytes (1- simple-fun-code-offset)))
      (inst byte 0))

    ;; The start of the actual code.
    ;; Save the return-pc.
    (popw rbp-tn (frame-word-offset return-pc-save-offset))

    ;; If copy-more-arg follows it will allocate the correct stack
    ;; size. The stack is not allocated first here as this may expose
    ;; args on the stack if they take up more space than the frame!
    (unless copy-more-arg-follows
      ;; The args fit within the frame so just allocate the frame.
      (inst lea rsp-tn
            (make-ea :qword :base rbp-tn
                     :disp (- (* n-word-bytes
                                 (max 3 (sb-allocated-size 'stack)))))))

    (trace-table-entry trace-table-normal)))

;;; This is emitted directly before either a known-call-local, call-local,
;;; or a multiple-call-local. All it does is allocate stack space for the
;;; callee (who has the same size stack as us).
(define-vop (allocate-frame)
  (:results (res :scs (any-reg control-stack))
            (nfp))
  (:info callee)
  (:ignore nfp callee)
  (:generator 2
    (move res rsp-tn)
    (inst sub rsp-tn (* n-word-bytes (sb-allocated-size 'stack)))))

;;; Allocate a partial frame for passing stack arguments in a full
;;; call. NARGS is the number of arguments passed. We allocate at
;;; least 3 slots, because the XEP noise is going to want to use them
;;; before it can extend the stack.
(define-vop (allocate-full-call-frame)
  (:info nargs)
  (:results (res :scs (any-reg control-stack)))
  (:generator 2
    (move res rsp-tn)
    (inst sub rsp-tn (* (max nargs 3) n-word-bytes))))
\f
;;; Emit code needed at the return-point from an unknown-values call
;;; for a fixed number of values. Values is the head of the TN-REF
;;; list for the locations that the values are to be received into.
;;; Nvals is the number of values that are to be received (should
;;; equal the length of Values).
;;;
;;; MOVE-TEMP is a DESCRIPTOR-REG TN used as a temporary.
;;;
;;; This code exploits the fact that in the unknown-values convention,
;;; a single value return returns at the return PC + 2, whereas a
;;; return of other than one value returns directly at the return PC.
;;;
;;; If 0 or 1 values are expected, then we just emit an instruction to
;;; reset the SP (which will only be executed when other than 1 value
;;; is returned.)
;;;
;;; In the general case we have to do three things:
;;;  -- Default unsupplied register values. This need only be done
;;;     when a single value is returned, since register values are
;;;     defaulted by the called in the non-single case.
;;;  -- Default unsupplied stack values. This needs to be done whenever
;;;     there are stack values.
;;;  -- Reset SP. This must be done whenever other than 1 value is
;;;     returned, regardless of the number of values desired.
(defun default-unknown-values (vop values nvals)
  (declare (type (or tn-ref null) values)
           (type unsigned-byte nvals))
  (cond
   ((<= nvals 1)
    (note-this-location vop :single-value-return)
    (inst cmov :c rsp-tn rbx-tn))
   ((<= nvals register-arg-count)
    (let ((regs-defaulted (gen-label)))
      (note-this-location vop :unknown-return)
      (inst jmp :c regs-defaulted)
      ;; Default the unsupplied registers.
      (let* ((2nd-tn-ref (tn-ref-across values))
             (2nd-tn (tn-ref-tn 2nd-tn-ref)))
        (inst mov 2nd-tn nil-value)
        (when (> nvals 2)
          (loop
            for tn-ref = (tn-ref-across 2nd-tn-ref)
            then (tn-ref-across tn-ref)
            for count from 2 below register-arg-count
            do (inst mov (tn-ref-tn tn-ref) 2nd-tn))))
      (inst mov rbx-tn rsp-tn)
      (emit-label regs-defaulted)
      (inst mov rsp-tn rbx-tn)))
   ((<= nvals 7)
    ;; The number of bytes depends on the relative jump instructions.
    ;; Best case is 31+(n-3)*14, worst case is 35+(n-3)*18. For
    ;; NVALS=6 that is 73/89 bytes, and for NVALS=7 that is 87/107
    ;; bytes which is likely better than using the blt below.
    (let ((regs-defaulted (gen-label))
          (defaulting-done (gen-label))
          (default-stack-slots (gen-label)))
      (note-this-location vop :unknown-return)
      ;; Branch off to the MV case.
      (inst jmp :c regs-defaulted)
      ;; Do the single value case.
      ;; Default the register args
      (inst mov rax-tn nil-value)
      (do ((i 1 (1+ i))
           (val (tn-ref-across values) (tn-ref-across val)))
          ((= i (min nvals register-arg-count)))
        (inst mov (tn-ref-tn val) rax-tn))

      ;; Fake other registers so it looks like we returned with all the
      ;; registers filled in.
      (move rbx-tn rsp-tn)
      (inst push rdx-tn)
      (inst jmp default-stack-slots)

      (emit-label regs-defaulted)

      (inst mov rax-tn nil-value)
      (storew rdx-tn rbx-tn -1)
      (collect ((defaults))
        (do ((i register-arg-count (1+ i))
             (val (do ((i 0 (1+ i))
                       (val values (tn-ref-across val)))
                      ((= i register-arg-count) val))
                  (tn-ref-across val)))
            ((null val))
          (let ((default-lab (gen-label))
                (tn (tn-ref-tn val)))
            (defaults (cons default-lab tn))

            (inst cmp rcx-tn (fixnumize i))
            (inst jmp :be default-lab)
            (loadw rdx-tn rbx-tn (frame-word-offset i))
            (inst mov tn rdx-tn)))

        (emit-label defaulting-done)
        (loadw rdx-tn rbx-tn -1)
        (move rsp-tn rbx-tn)

        (let ((defaults (defaults)))
          (when defaults
            (assemble (*elsewhere*)
              (trace-table-entry trace-table-fun-prologue)
              (emit-label default-stack-slots)
              (dolist (default defaults)
                (emit-label (car default))
                (inst mov (cdr default) rax-tn))
              (inst jmp defaulting-done)
              (trace-table-entry trace-table-normal)))))))
   (t
    (let ((regs-defaulted (gen-label))
          (restore-edi (gen-label))
          (no-stack-args (gen-label))
          (default-stack-vals (gen-label))
          (count-okay (gen-label)))
      (note-this-location vop :unknown-return)
      ;; Branch off to the MV case.
      (inst jmp :c regs-defaulted)

      ;; Default the register args, and set up the stack as if we
      ;; entered the MV return point.
      (inst mov rbx-tn rsp-tn)
      (inst push rdx-tn)
      (inst mov rdi-tn nil-value)
      (inst push rdi-tn)
      (inst mov rsi-tn rdi-tn)
      ;; Compute a pointer to where to put the [defaulted] stack values.
      (emit-label no-stack-args)
      (inst lea rdi-tn
            (make-ea :qword :base rbp-tn
                     :disp (frame-byte-offset register-arg-count)))
      ;; Load RAX with NIL so we can quickly store it, and set up
      ;; stuff for the loop.
      (inst mov rax-tn nil-value)
      (inst std)
      (inst mov rcx-tn (- nvals register-arg-count))
      ;; Jump into the default loop.
      (inst jmp default-stack-vals)

      ;; The regs are defaulted. We need to copy any stack arguments,
      ;; and then default the remaining stack arguments.
      (emit-label regs-defaulted)
      ;; Save EDI.
      (storew rdi-tn rbx-tn (frame-word-offset 1))
      ;; Compute the number of stack arguments, and if it's zero or
      ;; less, don't copy any stack arguments.
      (inst sub rcx-tn (fixnumize register-arg-count))
      (inst jmp :le no-stack-args)

      ;; Throw away any unwanted args.
      (inst cmp rcx-tn (fixnumize (- nvals register-arg-count)))
      (inst jmp :be count-okay)
      (inst mov rcx-tn (fixnumize (- nvals register-arg-count)))
      (emit-label count-okay)
      ;; Save the number of stack values.
      (inst mov rax-tn rcx-tn)
      ;; Compute a pointer to where the stack args go.
      (inst lea rdi-tn
            (make-ea :qword :base rbp-tn
                     :disp (frame-byte-offset register-arg-count)))
      ;; Save ESI, and compute a pointer to where the args come from.
      (storew rsi-tn rbx-tn (frame-word-offset 2))
      (inst lea rsi-tn
            (make-ea :qword :base rbx-tn
                     :disp (frame-byte-offset register-arg-count)))
      ;; Do the copy.
      (inst shr rcx-tn word-shift)              ; make word count
      (inst std)
      (inst rep)
      (inst movs :qword)
      ;; Restore RSI.
      (loadw rsi-tn rbx-tn (frame-word-offset 2))
      ;; Now we have to default the remaining args. Find out how many.
      (inst sub rax-tn (fixnumize (- nvals register-arg-count)))
      (inst neg rax-tn)
      ;; If none, then just blow out of here.
      (inst jmp :le restore-edi)
      (inst mov rcx-tn rax-tn)
      (inst shr rcx-tn word-shift)      ; word count
      ;; Load RAX with NIL for fast storing.
      (inst mov rax-tn nil-value)
      ;; Do the store.
      (emit-label default-stack-vals)
      (inst rep)
      (inst stos rax-tn)
      ;; Restore EDI, and reset the stack.
      (emit-label restore-edi)
      (loadw rdi-tn rbx-tn (frame-word-offset 1))
      (inst mov rsp-tn rbx-tn)
      (inst cld))))
  (values))
\f
;;;; unknown values receiving

;;; Emit code needed at the return point for an unknown-values call
;;; for an arbitrary number of values.
;;;
;;; We do the single and non-single cases with no shared code: there
;;; doesn't seem to be any potential overlap, and receiving a single
;;; value is more important efficiency-wise.
;;;
;;; When there is a single value, we just push it on the stack,
;;; returning the old SP and 1.
;;;
;;; When there is a variable number of values, we move all of the
;;; argument registers onto the stack, and return ARGS and NARGS.
;;;
;;; ARGS and NARGS are TNs wired to the named locations. We must
;;; explicitly allocate these TNs, since their lifetimes overlap with
;;; the results start and count. (Also, it's nice to be able to target
;;; them.)
(defun receive-unknown-values (args nargs start count)
  (declare (type tn args nargs start count))
  (let ((variable-values (gen-label))
        (done (gen-label)))
    (inst jmp :c variable-values)

    (cond ((location= start (first *register-arg-tns*))
           (inst push (first *register-arg-tns*))
           (inst lea start (make-ea :qword :base rsp-tn :disp n-word-bytes)))
          (t (inst mov start rsp-tn)
             (inst push (first *register-arg-tns*))))
    (inst mov count (fixnumize 1))
    (inst jmp done)

    (emit-label variable-values)
    ;; dtc: this writes the registers onto the stack even if they are
    ;; not needed, only the number specified in rcx are used and have
    ;; stack allocated to them. No harm is done.
    (loop
      for arg in *register-arg-tns*
      for i downfrom -1
      do (storew arg args i))
    (move start args)
    (move count nargs)

    (emit-label done))
  (values))

;;; VOP that can be inherited by unknown values receivers. The main thing this
;;; handles is allocation of the result temporaries.
(define-vop (unknown-values-receiver)
  (:temporary (:sc descriptor-reg :offset rbx-offset
                   :from :eval :to (:result 0))
              values-start)
  (:temporary (:sc any-reg :offset rcx-offset
               :from :eval :to (:result 1))
              nvals)
  (:results (start :scs (any-reg control-stack))
            (count :scs (any-reg control-stack))))
\f
;;;; local call with unknown values convention return

;;; Non-TR local call for a fixed number of values passed according to
;;; the unknown values convention.
;;;
;;; FP is the frame pointer in install before doing the call.
;;;
;;; NFP would be the number-stack frame pointer if we had a separate
;;; number stack.
;;;
;;; Args are the argument passing locations, which are specified only
;;; to terminate their lifetimes in the caller.
;;;
;;; VALUES are the return value locations (wired to the standard
;;; passing locations). NVALS is the number of values received.
;;;
;;; Save is the save info, which we can ignore since saving has been
;;; done.
;;;
;;; TARGET is a continuation pointing to the start of the called
;;; function.
(define-vop (call-local)
  (:args (fp)
         (nfp)
         (args :more t))
  (:temporary (:sc unsigned-reg) return-label)
  (:results (values :more t))
  (:save-p t)
  (:move-args :local-call)
  (:info arg-locs callee target nvals)
  (:vop-var vop)
  (:ignore nfp arg-locs args #+nil callee)
  (:generator 5
    (trace-table-entry trace-table-call-site)
    (move rbp-tn fp)

    (let ((ret-tn (callee-return-pc-tn callee)))
      #+nil
      (format t "*call-local ~S; tn-kind ~S; tn-save-tn ~S; its tn-kind ~S~%"
              ret-tn (sb!c::tn-kind ret-tn) (sb!c::tn-save-tn ret-tn)
              (sb!c::tn-kind (sb!c::tn-save-tn ret-tn)))

      ;; Is the return-pc on the stack or in a register?
      (sc-case ret-tn
        ((sap-stack)
         (unless (= (tn-offset ret-tn) return-pc-save-offset)
           (error "ret-tn ~A in wrong stack slot" ret-tn))
         #+nil (format t "*call-local: ret-tn on stack; offset=~S~%"
                       (tn-offset ret-tn))
         (inst lea return-label (make-fixup nil :code-object RETURN))
         (storew return-label rbp-tn (frame-word-offset (tn-offset ret-tn))))
        (t
         (error "ret-tn ~A in sap-reg" ret-tn))))

    (note-this-location vop :call-site)
    (inst jmp target)
    RETURN
    (default-unknown-values vop values nvals)
    (trace-table-entry trace-table-normal)))

;;; Non-TR local call for a variable number of return values passed according
;;; to the unknown values convention. The results are the start of the values
;;; glob and the number of values received.
(define-vop (multiple-call-local unknown-values-receiver)
  (:args (fp)
         (nfp)
         (args :more t))
  (:temporary (:sc unsigned-reg) return-label)
  (:save-p t)
  (:move-args :local-call)
  (:info save callee target)
  (:ignore args save nfp #+nil callee)
  (:vop-var vop)
  (:generator 20
    (trace-table-entry trace-table-call-site)
    (move rbp-tn fp)

    (let ((ret-tn (callee-return-pc-tn callee)))
      #+nil
      (format t "*multiple-call-local ~S; tn-kind ~S; tn-save-tn ~S; its tn-kind ~S~%"
              ret-tn (sb!c::tn-kind ret-tn) (sb!c::tn-save-tn ret-tn)
              (sb!c::tn-kind (sb!c::tn-save-tn ret-tn)))

      ;; Is the return-pc on the stack or in a register?
      (sc-case ret-tn
        ((sap-stack)
         #+nil (format t "*multiple-call-local: ret-tn on stack; offset=~S~%"
                       (tn-offset ret-tn))
         ;; Stack
         (inst lea return-label (make-fixup nil :code-object RETURN))
         (storew return-label rbp-tn (frame-word-offset (tn-offset ret-tn))))
        (t
         (error "multiple-call-local: return-pc not on stack."))))

    (note-this-location vop :call-site)
    (inst jmp target)
    RETURN
    (note-this-location vop :unknown-return)
    (receive-unknown-values values-start nvals start count)
    (trace-table-entry trace-table-normal)))
\f
;;;; local call with known values return

;;; Non-TR local call with known return locations. Known-value return
;;; works just like argument passing in local call.
;;;
;;; Note: we can't use normal load-tn allocation for the fixed args,
;;; since all registers may be tied up by the more operand. Instead,
;;; we use MAYBE-LOAD-STACK-TN.
(define-vop (known-call-local)
  (:args (fp)
         (nfp)
         (args :more t))
  (:temporary (:sc unsigned-reg) return-label)
  (:results (res :more t))
  (:move-args :local-call)
  (:save-p t)
  (:info save callee target)
  (:ignore args res save nfp #+nil callee)
  (:vop-var vop)
  (:generator 5
    (trace-table-entry trace-table-call-site)
    (move rbp-tn fp)

    (let ((ret-tn (callee-return-pc-tn callee)))

      #+nil
      (format t "*known-call-local ~S; tn-kind ~S; tn-save-tn ~S; its tn-kind ~S~%"
              ret-tn (sb!c::tn-kind ret-tn) (sb!c::tn-save-tn ret-tn)
              (sb!c::tn-kind (sb!c::tn-save-tn ret-tn)))

      ;; Is the return-pc on the stack or in a register?
      (sc-case ret-tn
        ((sap-stack)
         #+nil (format t "*known-call-local: ret-tn on stack; offset=~S~%"
                       (tn-offset ret-tn))
         ;; Stack
         (inst lea return-label (make-fixup nil :code-object RETURN))
         (storew return-label rbp-tn (frame-word-offset (tn-offset ret-tn))))
        (t
         (error "known-call-local: return-pc not on stack."))))

    (note-this-location vop :call-site)
    (inst jmp target)
    RETURN
    (note-this-location vop :known-return)
    (trace-table-entry trace-table-normal)))
\f
;;; Return from known values call. We receive the return locations as
;;; arguments to terminate their lifetimes in the returning function. We
;;; restore FP and CSP and jump to the Return-PC.
;;;
;;; We can assume we know exactly where old-fp and return-pc are because
;;; make-old-fp-save-location and make-return-pc-save-location always
;;; return the same place.
#+nil
(define-vop (known-return)
  (:args (old-fp)
         (return-pc :scs (any-reg immediate-stack) :target rpc)
         (vals :more t))
  (:move-args :known-return)
  (:info val-locs)
  (:temporary (:sc unsigned-reg :from (:argument 1)) rpc)
  (:ignore val-locs vals)
  (:vop-var vop)
  (:generator 6
    (trace-table-entry trace-table-fun-epilogue)
    ;; Save the return-pc in a register 'cause the frame-pointer is
    ;; going away. Note this not in the usual stack location so we
    ;; can't use RET
    (move rpc return-pc)
    ;; Restore the stack.
    (move rsp-tn rbp-tn)
    ;; Restore the old fp. We know OLD-FP is going to be in its stack
    ;; save slot, which is a different frame that than this one,
    ;; so we don't have to worry about having just cleared
    ;; most of the stack.
    (move rbp-tn old-fp)
    (inst jmp rpc)
    (trace-table-entry trace-table-normal)))
\f
;;; From Douglas Crosher
;;; Return from known values call. We receive the return locations as
;;; arguments to terminate their lifetimes in the returning function. We
;;; restore FP and CSP and jump to the Return-PC.
;;;
;;; The old-fp may be either in a register or on the stack in its
;;; standard save locations - slot 0.
;;;
;;; The return-pc may be in a register or on the stack in any slot.
(define-vop (known-return)
  (:args (old-fp)
         (return-pc)
         (vals :more t))
  (:move-args :known-return)
  (:info val-locs)
  (:ignore val-locs vals)
  (:vop-var vop)
  (:generator 6
    (trace-table-entry trace-table-fun-epilogue)
    ;; return-pc may be either in a register or on the stack.
    (sc-case return-pc
      ((sap-stack)
       (unless (and (sc-is old-fp control-stack)
                    (= (tn-offset old-fp) ocfp-save-offset))
         (error "known-return: ocfp not on stack in standard save location?"))
       (unless (and (sc-is return-pc sap-stack)
                    (= (tn-offset return-pc) return-pc-save-offset))
         (error
          "known-return: return-pc not on stack in standard save location?"))

       ;; Zot all of the stack except for the old-fp and return-pc.
       (inst lea rsp-tn
             (make-ea :qword :base rbp-tn
                      :disp (frame-byte-offset ocfp-save-offset)))
       (inst pop rbp-tn)
       (inst ret (* (tn-offset return-pc) n-word-bytes)))
      (t
       (error "known-return, return-pc not on stack")))

    (trace-table-entry trace-table-normal)))
\f
;;;; full call
;;;
;;; There is something of a cross-product effect with full calls.
;;; Different versions are used depending on whether we know the
;;; number of arguments or the name of the called function, and
;;; whether we want fixed values, unknown values, or a tail call.
;;;
;;; In full call, the arguments are passed creating a partial frame on
;;; the stack top and storing stack arguments into that frame. On
;;; entry to the callee, this partial frame is pointed to by FP.

;;; This macro helps in the definition of full call VOPs by avoiding
;;; code replication in defining the cross-product VOPs.
;;;
;;; NAME is the name of the VOP to define.
;;;
;;; NAMED is true if the first argument is an fdefinition object whose
;;; definition is to be called.
;;;
;;; RETURN is either :FIXED, :UNKNOWN or :TAIL:
;;; -- If :FIXED, then the call is for a fixed number of values, returned in
;;;    the standard passing locations (passed as result operands).
;;; -- If :UNKNOWN, then the result values are pushed on the stack, and the
;;;    result values are specified by the Start and Count as in the
;;;    unknown-values continuation representation.
;;; -- If :TAIL, then do a tail-recursive call. No values are returned.
;;;    The Old-Fp and Return-PC are passed as the second and third arguments.
;;;
;;; In non-tail calls, the pointer to the stack arguments is passed as
;;; the last fixed argument. If Variable is false, then the passing
;;; locations are passed as a more arg. Variable is true if there are
;;; a variable number of arguments passed on the stack. Variable
;;; cannot be specified with :TAIL return. TR variable argument call
;;; is implemented separately.
;;;
;;; In tail call with fixed arguments, the passing locations are
;;; passed as a more arg, but there is no new-FP, since the arguments
;;; have been set up in the current frame.
(macrolet ((define-full-call (name named return variable)
            (aver (not (and variable (eq return :tail))))
            `(define-vop (,name
                          ,@(when (eq return :unknown)
                              '(unknown-values-receiver)))
               (:args
               ,@(unless (eq return :tail)
                   '((new-fp :scs (any-reg) :to (:argument 1))))

               (fun :scs (descriptor-reg control-stack)
                    :target rax :to (:argument 0))

               ,@(when (eq return :tail)
                   '((old-fp)
                     (return-pc)))

               ,@(unless variable '((args :more t :scs (descriptor-reg)))))

               ,@(when (eq return :fixed)
               '((:results (values :more t))))

               (:save-p ,(if (eq return :tail) :compute-only t))

               ,@(unless (or (eq return :tail) variable)
               '((:move-args :full-call)))

               (:vop-var vop)
               (:info
               ,@(unless (or variable (eq return :tail)) '(arg-locs))
               ,@(unless variable '(nargs))
               ,@(when (eq return :fixed) '(nvals))
               step-instrumenting)

               (:ignore
               ,@(unless (or variable (eq return :tail)) '(arg-locs))
               ,@(unless variable '(args)))

               ;; We pass either the fdefn object (for named call) or
               ;; the actual function object (for unnamed call) in
               ;; RAX. With named call, closure-tramp will replace it
               ;; with the real function and invoke the real function
               ;; for closures. Non-closures do not need this value,
               ;; so don't care what shows up in it.
               (:temporary
               (:sc descriptor-reg
                    :offset rax-offset
                    :from (:argument 0)
                    :to :eval)
               rax)

               ;; We pass the number of arguments in RCX.
               (:temporary (:sc unsigned-reg :offset rcx-offset :to :eval) rcx)

               ;; With variable call, we have to load the
               ;; register-args out of the (new) stack frame before
               ;; doing the call. Therefore, we have to tell the
               ;; lifetime stuff that we need to use them.
               ,@(when variable
                   (mapcar (lambda (name offset)
                             `(:temporary (:sc descriptor-reg
                                               :offset ,offset
                                               :from (:argument 0)
                                               :to :eval)
                                          ,name))
                           *register-arg-names* *register-arg-offsets*))

               ,@(when (eq return :tail)
                   '((:temporary (:sc unsigned-reg
                                      :from (:argument 1)
                                      :to (:argument 2))
                                 old-fp-tmp)))

               (:generator ,(+ (if named 5 0)
                               (if variable 19 1)
                               (if (eq return :tail) 0 10)
                               15
                               (if (eq return :unknown) 25 0))
               (trace-table-entry trace-table-call-site)

               ;; This has to be done before the frame pointer is
               ;; changed! RAX stores the 'lexical environment' needed
               ;; for closures.
               (move rax fun)


               ,@(if variable
                     ;; For variable call, compute the number of
                     ;; arguments and move some of the arguments to
                     ;; registers.
                     (collect ((noise))
                              ;; Compute the number of arguments.
                              (noise '(inst mov rcx new-fp))
                              (noise '(inst sub rcx rsp-tn))
                              ;; Move the necessary args to registers,
                              ;; this moves them all even if they are
                              ;; not all needed.
                              (loop
                               for name in *register-arg-names*
                               for index downfrom -1
                               do (noise `(loadw ,name new-fp ,index)))
                              (noise))
                   '((if (zerop nargs)
                         (zeroize rcx)
                       (inst mov rcx (fixnumize nargs)))))
               ,@(cond ((eq return :tail)
                        '(;; Python has figured out what frame we should
                          ;; return to so might as well use that clue.
                          ;; This seems really important to the
                          ;; implementation of things like
                          ;; (without-interrupts ...)
                          ;;
                          ;; dtc; Could be doing a tail call from a
                          ;; known-local-call etc in which the old-fp
                          ;; or ret-pc are in regs or in non-standard
                          ;; places. If the passing location were
                          ;; wired to the stack in standard locations
                          ;; then these moves will be un-necessary;
                          ;; this is probably best for the x86.
                          (sc-case old-fp
                                   ((control-stack)
                                    (unless (= ocfp-save-offset
                                               (tn-offset old-fp))
                                      ;; FIXME: FORMAT T for stale
                                      ;; diagnostic output (several of
                                      ;; them around here), ick
                                      (error "** tail-call old-fp not S0~%")
                                      (move old-fp-tmp old-fp)
                                      (storew old-fp-tmp
                                              rbp-tn
                                              (frame-word-offset ocfp-save-offset))))
                                   ((any-reg descriptor-reg)
                                    (error "** tail-call old-fp in reg not S0~%")
                                    (storew old-fp
                                            rbp-tn
                                            (frame-word-offset ocfp-save-offset))))

                          ;; For tail call, we have to push the
                          ;; return-pc so that it looks like we CALLed
                          ;; despite the fact that we are going to JMP.
                          (inst push return-pc)
                          ))
                       (t
                        ;; For non-tail call, we have to save our
                        ;; frame pointer and install the new frame
                        ;; pointer. We can't load stack tns after this
                        ;; point.
                        `(;; Python doesn't seem to allocate a frame
                          ;; here which doesn't leave room for the
                          ;; ofp/ret stuff.

                          ;; The variable args are on the stack and
                          ;; become the frame, but there may be <3
                          ;; args and 3 stack slots are assumed
                          ;; allocate on the call. So need to ensure
                          ;; there are at least 3 slots. This hack
                          ;; just adds 3 more.
                          ,(if variable
                               '(inst sub rsp-tn (fixnumize 3)))

                          ;; Save the fp
                          (storew rbp-tn new-fp
                                  (frame-word-offset ocfp-save-offset))

                          (move rbp-tn new-fp) ; NB - now on new stack frame.
                          )))

               (when step-instrumenting
                 (emit-single-step-test)
                 (inst jmp :eq DONE)
                 (inst break single-step-around-trap))
               DONE

               (note-this-location vop :call-site)

               (inst ,(if (eq return :tail) 'jmp 'call)
                     (make-ea :qword :base rax
                              :disp ,(if named
                                         '(- (* fdefn-raw-addr-slot
                                                n-word-bytes)
                                             other-pointer-lowtag)
                                       '(- (* closure-fun-slot n-word-bytes)
                                           fun-pointer-lowtag))))
               ,@(ecase return
                   (:fixed
                    '((default-unknown-values vop values nvals)))
                   (:unknown
                    '((note-this-location vop :unknown-return)
                      (receive-unknown-values values-start nvals start count)))
                   (:tail))
               (trace-table-entry trace-table-normal)))))

  (define-full-call call nil :fixed nil)
  (define-full-call call-named t :fixed nil)
  (define-full-call multiple-call nil :unknown nil)
  (define-full-call multiple-call-named t :unknown nil)
  (define-full-call tail-call nil :tail nil)
  (define-full-call tail-call-named t :tail nil)

  (define-full-call call-variable nil :fixed t)
  (define-full-call multiple-call-variable nil :unknown t))

;;; This is defined separately, since it needs special code that BLT's
;;; the arguments down. All the real work is done in the assembly
;;; routine. We just set things up so that it can find what it needs.
(define-vop (tail-call-variable)
  (:args (args :scs (any-reg control-stack) :target rsi)
         (function :scs (descriptor-reg control-stack) :target rax)
         (old-fp)
         (ret-addr))
  (:temporary (:sc unsigned-reg :offset rsi-offset :from (:argument 0)) rsi)
  (:temporary (:sc unsigned-reg :offset rax-offset :from (:argument 1)) rax)
  (:temporary (:sc unsigned-reg) call-target)
;  (:ignore ret-addr old-fp)
  (:generator 75
    ;; Move these into the passing locations if they are not already there.
    (move rsi args)
    (move rax function)

    ;; The following assumes that the return-pc and old-fp are on the
    ;; stack in their standard save locations - Check this.
    (unless (and (sc-is old-fp control-stack)
                 (= (tn-offset old-fp) ocfp-save-offset))
            (error "tail-call-variable: ocfp not on stack in standard save location?"))
    (unless (and (sc-is ret-addr sap-stack)
                 (= (tn-offset ret-addr) return-pc-save-offset))
            (error "tail-call-variable: ret-addr not on stack in standard save location?"))


    (inst lea call-target
          (make-ea :qword
                   :disp (make-fixup 'tail-call-variable :assembly-routine)))
    ;; And jump to the assembly routine.
    (inst jmp call-target)))
\f
;;;; unknown values return

;;; Return a single-value using the Unknown-Values convention.
;;;
;;; pfw--get wired-tn conflicts sometimes if register sc specd for args
;;; having problems targeting args to regs -- using temps instead.
;;;
;;; First off, modifying the return-pc defeats the branch-prediction
;;; optimizations on modern CPUs quite handily. Second, we can do all
;;; this without needing a temp register. Fixed the latter, at least.
;;; -- AB 2006/Feb/04
(define-vop (return-single)
  (:args (old-fp)
         (return-pc)
         (value))
  (:ignore value)
  (:generator 6
    (trace-table-entry trace-table-fun-epilogue)
    ;; Code structure lifted from known-return.
    (sc-case return-pc
      ((sap-stack)
       ;; Note that this will only work right if, when old-fp is on
       ;; the stack, it has a lower tn-offset than return-pc. One of
       ;; the comments in known-return indicate that this is the case
       ;; (in that it will be in its save location), but we may wish
       ;; to assert that (in either the weaker or stronger forms).
       ;; Should this ever not be the case, we should load old-fp into
       ;; a temp reg while we fix the stack.
       (unless (and (sc-is old-fp control-stack)
                    (= (tn-offset old-fp) ocfp-save-offset))
         (error "ocfp not on stack in standard save location?"))
       (unless (and (sc-is return-pc sap-stack)
                    (= (tn-offset return-pc) return-pc-save-offset))
         (error "return-pc not on stack in standard save location?"))
       ;; Drop stack above old-fp
       (inst lea rsp-tn (make-ea :qword :base rbp-tn
                                 :disp (frame-byte-offset (tn-offset old-fp))))
       ;; Set single-value return flag
       (inst clc)
       ;; Restore the old frame pointer
       (inst pop rbp-tn)
       ;; And return, dropping the rest of the stack as we go.
       (inst ret (* (tn-offset return-pc) n-word-bytes)))
      (t
       (error "return pc not on stack")))))

;;; Do unknown-values return of a fixed (other than 1) number of
;;; values. The VALUES are required to be set up in the standard
;;; passing locations. NVALS is the number of values returned.
;;;
;;; Basically, we just load RCX with the number of values returned and
;;; RBX with a pointer to the values, set RSP to point to the end of
;;; the values, and jump directly to return-pc.
(define-vop (return)
  (:args (old-fp)
         (return-pc :to (:eval 1))
         (values :more t))
  (:ignore values)
  (:info nvals)

  ;; In the case of other than one value, we need these registers to
  ;; tell the caller where they are and how many there are.
  (:temporary (:sc unsigned-reg :offset rbx-offset) rbx)
  (:temporary (:sc unsigned-reg :offset rcx-offset) rcx)

  ;; We need to stretch the lifetime of return-pc past the argument
  ;; registers so that we can default the argument registers without
  ;; trashing return-pc.
  (:temporary (:sc unsigned-reg :offset (first *register-arg-offsets*)
                   :from :eval) a0)
  (:temporary (:sc unsigned-reg :offset (second *register-arg-offsets*)
                   :from :eval) a1)
  (:temporary (:sc unsigned-reg :offset (third *register-arg-offsets*)
                   :from :eval) a2)

  (:generator 6
    (trace-table-entry trace-table-fun-epilogue)
    ;; Establish the values pointer and values count.
    (move rbx rbp-tn)
    (if (zerop nvals)
        (zeroize rcx) ; smaller
      (inst mov rcx (fixnumize nvals)))
    ;; Restore the frame pointer.
    (move rbp-tn old-fp)
    ;; Clear as much of the stack as possible, but not past the return
    ;; address.
    (inst lea rsp-tn
          (make-ea :qword :base rbx
                   :disp (frame-byte-offset (max (1- nvals)
                                                 return-pc-save-offset))))
    ;; Pre-default any argument register that need it.
    (when (< nvals register-arg-count)
      (let* ((arg-tns (nthcdr nvals (list a0 a1 a2)))
             (first (first arg-tns)))
        (inst mov first nil-value)
        (dolist (tn (cdr arg-tns))
          (inst mov tn first))))
    ;; Set the multiple value return flag.
    (inst stc)
    ;; And away we go. Except that return-pc is still on the
    ;; stack and we've changed the stack pointer. So we have to
    ;; tell it to index off of RBX instead of RBP.
    (cond ((zerop nvals)
           ;; Return popping the return address and what's earlier in
           ;; the frame.
           (inst ret (* return-pc-save-offset n-word-bytes)))
          ((= nvals 1)
           ;; This is handled in RETURN-SINGLE.
           (error "nvalues is 1"))
          (t
           ;; Thou shalt not JMP unto thy return address.
           (inst push (make-ea :qword :base rbx
                               :disp (frame-byte-offset (tn-offset return-pc))))
           (inst ret)))

    (trace-table-entry trace-table-normal)))

;;; Do unknown-values return of an arbitrary number of values (passed
;;; on the stack.) We check for the common case of a single return
;;; value, and do that inline using the normal single value return
;;; convention. Otherwise, we branch off to code that calls an
;;; assembly-routine.
;;;
;;; The assembly routine takes the following args:
;;;  RAX -- the return-pc to finally jump to.
;;;  RBX -- pointer to where to put the values.
;;;  RCX -- number of values to find there.
;;;  RSI -- pointer to where to find the values.
(define-vop (return-multiple)
  (:args (old-fp :to (:eval 1) :target old-fp-temp)
         (return-pc :target rax)
         (vals :scs (any-reg) :target rsi)
         (nvals :scs (any-reg) :target rcx))

  (:temporary (:sc unsigned-reg :offset rax-offset :from (:argument 1)) rax)
  (:temporary (:sc unsigned-reg :offset rsi-offset :from (:argument 2)) rsi)
  (:temporary (:sc unsigned-reg :offset rcx-offset :from (:argument 3)) rcx)
  (:temporary (:sc unsigned-reg :offset rbx-offset :from (:eval 0)) rbx)
  (:temporary (:sc unsigned-reg) return-asm)
  (:temporary (:sc descriptor-reg :offset (first *register-arg-offsets*)
                   :from (:eval 0)) a0)
  (:temporary (:sc unsigned-reg :from (:eval 1)) old-fp-temp)
  (:node-var node)

  (:generator 13
    (trace-table-entry trace-table-fun-epilogue)
    ;; Load the return-pc.
    (move rax return-pc)
    (unless (policy node (> space speed))
      ;; Check for the single case.
      (let ((not-single (gen-label)))
        (inst cmp nvals (fixnumize 1))
        (inst jmp :ne not-single)

        ;; Return with one value.
        (loadw a0 vals -1)
        ;; Clear the stack. We load old-fp into a register before clearing
        ;; the stack.
        (move old-fp-temp old-fp)
        (move rsp-tn rbp-tn)
        (move rbp-tn old-fp-temp)
        ;; clear the multiple-value return flag
        (inst clc)
        ;; Out of here.
        (inst push rax)
        (inst ret)
        ;; Nope, not the single case. Jump to the assembly routine.
        (emit-label not-single)))
    (move rsi vals)
    (move rcx nvals)
    (move rbx rbp-tn)
    (move rbp-tn old-fp)
    (inst lea return-asm
          (make-ea :qword :disp (make-fixup 'return-multiple
                                            :assembly-routine)))
    (inst jmp return-asm)
    (trace-table-entry trace-table-normal)))
\f
;;;; XEP hackery

;;; We don't need to do anything special for regular functions.
(define-vop (setup-environment)
  (:info label)
  (:ignore label)
  (:generator 0
    ;; Don't bother doing anything.
    nil))

;;; Get the lexical environment from its passing location.
(define-vop (setup-closure-environment)
  (:results (closure :scs (descriptor-reg)))
  (:info label)
  (:ignore label)
  (:generator 6
    ;; Get result.
    (move closure rax-tn)))

;;; Copy a &MORE arg from the argument area to the end of the current
;;; frame. FIXED is the number of non-&MORE arguments.
(define-vop (copy-more-arg)
  (:temporary (:sc any-reg :offset r8-offset) copy-index)
  (:temporary (:sc any-reg :offset r9-offset) source)
  (:temporary (:sc descriptor-reg :offset r10-offset) temp)
  (:info fixed)
  (:generator 20
    ;; Avoid the copy if there are no more args.
    (cond ((zerop fixed)
           (inst jrcxz JUST-ALLOC-FRAME))
          (t
           (inst cmp rcx-tn (fixnumize fixed))
           (inst jmp :be JUST-ALLOC-FRAME)))

    ;; Allocate the space on the stack.
    ;; stack = rbp - (max 3 frame-size) - (nargs - fixed)
    (inst lea rbx-tn
          (make-ea :qword :base rbp-tn
                   :disp (- (fixnumize fixed)
                            (* n-word-bytes
                               (max 3 (sb-allocated-size 'stack))))))
    (inst sub rbx-tn rcx-tn)  ; Got the new stack in rbx
    (inst mov rsp-tn rbx-tn)

    ;; Now: nargs>=1 && nargs>fixed

    ;; Save the original count of args.
    (inst mov rbx-tn rcx-tn)

    (cond ((< fixed register-arg-count)
           ;; We must stop when we run out of stack args, not when we
           ;; run out of more args.
           ;; Number to copy = nargs-3
           (inst sub rcx-tn (fixnumize register-arg-count))
           ;; Everything of interest in registers.
           (inst jmp :be DO-REGS))
          (t
           ;; Number to copy = nargs-fixed
           (inst sub rcx-tn (fixnumize fixed))))

    ;; Initialize R8 to be the end of args.
    (inst mov source rbp-tn)
    (inst sub source rbx-tn)

    ;; We need to copy from downwards up to avoid overwriting some of
    ;; the yet uncopied args. So we need to use R9 as the copy index
    ;; and RCX as the loop counter, rather than using RCX for both.
    (zeroize copy-index)

    ;; We used to use REP MOVS here, but on modern x86 it performs
    ;; much worse than an explicit loop for small blocks.
    COPY-LOOP
    (inst mov temp (make-ea :qword :base source :index copy-index))
    (inst mov (make-ea :qword :base rsp-tn :index copy-index) temp)
    (inst add copy-index n-word-bytes)
    (inst sub rcx-tn n-word-bytes)
    (inst jmp :nz COPY-LOOP)

    DO-REGS

    ;; Restore RCX
    (inst mov rcx-tn rbx-tn)

    ;; Here: nargs>=1 && nargs>fixed
    (when (< fixed register-arg-count)
      ;; Now we have to deposit any more args that showed up in
      ;; registers.
      (do ((i fixed))
          ( nil )
        ;; Store it relative to rbp
        (inst mov (make-ea :qword :base rbp-tn
                           :disp (- (* n-word-bytes
                                       (+ 1 (- i fixed)
                                          (max 3 (sb-allocated-size 'stack))))))
              (nth i *register-arg-tns*))

        (incf i)
        (when (>= i register-arg-count)
          (return))

        ;; Don't deposit any more than there are.
        (if (zerop i)
            (inst test rcx-tn rcx-tn)
            (inst cmp rcx-tn (fixnumize i)))
        (inst jmp :eq DONE)))

    (inst jmp DONE)

    JUST-ALLOC-FRAME
    (inst lea rsp-tn
          (make-ea :qword :base rbp-tn
                   :disp (- (* n-word-bytes
                               (max 3 (sb-allocated-size 'stack))))))

    DONE))

(define-vop (more-kw-arg)
  (:translate sb!c::%more-kw-arg)
  (:policy :fast-safe)
  (:args (object :scs (descriptor-reg) :to (:result 1))
         (index :scs (any-reg) :to (:result 1) :target keyword))
  (:arg-types * tagged-num)
  (:results (value :scs (descriptor-reg any-reg))
            (keyword :scs (descriptor-reg any-reg)))
  (:result-types * *)
  (:generator 4
     (inst mov value (make-ea :qword :base object :index index))
     (inst mov keyword (make-ea :qword :base object :index index
                                :disp n-word-bytes))))

(define-vop (more-arg)
    (:translate sb!c::%more-arg)
  (:policy :fast-safe)
  (:args (object :scs (descriptor-reg) :to (:result 1))
         (index :scs (any-reg) :to (:result 1) :target value))
  (:arg-types * tagged-num)
  (:results (value :scs (descriptor-reg any-reg)))
  (:result-types *)
  (:generator 4
    (move value index)
    (inst neg value)
    (inst mov value (make-ea :qword :base object :index value))))

;;; Turn more arg (context, count) into a list.
(define-vop (listify-rest-args)
  (:translate %listify-rest-args)
  (:policy :safe)
  (:args (context :scs (descriptor-reg) :target src)
         (count :scs (any-reg) :target rcx))
  (:arg-types * tagged-num)
  (:temporary (:sc unsigned-reg :offset rsi-offset :from (:argument 0)) src)
  (:temporary (:sc unsigned-reg :offset rcx-offset :from (:argument 1)) rcx)
  (:temporary (:sc unsigned-reg :offset rax-offset) rax)
  (:temporary (:sc unsigned-reg) dst)
  (:results (result :scs (descriptor-reg)))
  (:node-var node)
  (:generator 20
    (let ((enter (gen-label))
          (loop (gen-label))
          (done (gen-label))
          (stack-allocate-p (node-stack-allocate-p node)))
      (move src context)
      (move rcx count)
      ;; Check to see whether there are no args, and just return NIL if so.
      (inst mov result nil-value)
      (inst jrcxz done)
      (inst lea dst (make-ea :qword :base rcx :index rcx))
      (maybe-pseudo-atomic stack-allocate-p
       (allocation dst dst node stack-allocate-p list-pointer-lowtag)
       (inst shr rcx (1- n-lowtag-bits))
       ;; Set decrement mode (successive args at lower addresses)
       (inst std)
       ;; Set up the result.
       (move result dst)
       ;; Jump into the middle of the loop, 'cause that's where we want
       ;; to start.
       (inst jmp enter)
       (emit-label loop)
       ;; Compute a pointer to the next cons.
       (inst add dst (* cons-size n-word-bytes))
       ;; Store a pointer to this cons in the CDR of the previous cons.
       (storew dst dst -1 list-pointer-lowtag)
       (emit-label enter)
       ;; Grab one value and stash it in the car of this cons.
       (inst lods rax)
       (storew rax dst 0 list-pointer-lowtag)
       ;; Go back for more.
       (inst sub rcx 1)
       (inst jmp :nz loop)
       ;; NIL out the last cons.
       (storew nil-value dst 1 list-pointer-lowtag)
       (inst cld))
      (emit-label done))))

;;; Return the location and size of the &MORE arg glob created by
;;; COPY-MORE-ARG. SUPPLIED is the total number of arguments supplied
;;; (originally passed in RCX). FIXED is the number of non-rest
;;; arguments.
;;;
;;; We must duplicate some of the work done by COPY-MORE-ARG, since at
;;; that time the environment is in a pretty brain-damaged state,
;;; preventing this info from being returned as values. What we do is
;;; compute supplied - fixed, and return a pointer that many words
;;; below the current stack top.
(define-vop (more-arg-context)
  (:policy :fast-safe)
  (:translate sb!c::%more-arg-context)
  (:args (supplied :scs (any-reg) :target count))
  (:arg-types positive-fixnum (:constant fixnum))
  (:info fixed)
  (:results (context :scs (descriptor-reg))
            (count :scs (any-reg)))
  (:result-types t tagged-num)
  (:note "more-arg-context")
  (:generator 5
    (move count supplied)
    ;; SP at this point points at the last arg pushed.
    ;; Point to the first more-arg, not above it.
    (inst lea context (make-ea :qword :base rsp-tn
                               :index count :scale 1
                               :disp (- (+ (fixnumize fixed) n-word-bytes))))
    (unless (zerop fixed)
      (inst sub count (fixnumize fixed)))))

;;; Signal wrong argument count error if NARGS isn't equal to COUNT.
(define-vop (verify-arg-count)
  (:policy :fast-safe)
  (:translate sb!c::%verify-arg-count)
  (:args (nargs :scs (any-reg)))
  (:arg-types positive-fixnum (:constant t))
  (:info count)
  (:vop-var vop)
  (:save-p :compute-only)
  (:generator 3
    (let ((err-lab
           (generate-error-code vop 'invalid-arg-count-error nargs)))
      (if (zerop count)
          (inst test nargs nargs)  ; smaller instruction
        (inst cmp nargs (fixnumize count)))
      (inst jmp :ne err-lab))))

;;; Various other error signallers.
(macrolet ((def (name error translate &rest args)
             `(define-vop (,name)
                ,@(when translate
                    `((:policy :fast-safe)
                      (:translate ,translate)))
                (:args ,@(mapcar (lambda (arg)
                                   `(,arg :scs (any-reg descriptor-reg)))
                                 args))
                (:vop-var vop)
                (:save-p :compute-only)
                (:generator 1000
                  (error-call vop ',error ,@args)))))
  (def arg-count-error invalid-arg-count-error
    sb!c::%arg-count-error nargs)
  (def type-check-error object-not-type-error sb!c::%type-check-error
    object type)
  (def layout-invalid-error layout-invalid-error sb!c::%layout-invalid-error
    object layout)
  (def odd-key-args-error odd-key-args-error
    sb!c::%odd-key-args-error)
  (def unknown-key-arg-error unknown-key-arg-error
    sb!c::%unknown-key-arg-error key)
  (def nil-fun-returned-error nil-fun-returned-error nil fun))

;;; Single-stepping

(defun emit-single-step-test ()
  ;; We use different ways of representing whether stepping is on on
  ;; +SB-THREAD / -SB-THREAD: on +SB-THREAD, we use a slot in the
  ;; thread structure. On -SB-THREAD we use the value of a static
  ;; symbol. Things are done this way, since reading a thread-local
  ;; slot from a symbol would require an extra register on +SB-THREAD,
  ;; and reading a slot from a thread structure would require an extra
  ;; register on -SB-THREAD. While this isn't critical for x86-64,
  ;; it's more serious for x86.
  #!+sb-thread
  (inst cmp (make-ea :qword
                     :base thread-base-tn
                     :disp (* thread-stepping-slot n-word-bytes))
        nil-value)
  #!-sb-thread
  (inst cmp (make-ea :qword
                     :disp (+ nil-value (static-symbol-offset
                                         'sb!impl::*stepping*)
                              (* symbol-value-slot n-word-bytes)
                              (- other-pointer-lowtag)))
        nil-value))

(define-vop (step-instrument-before-vop)
  (:policy :fast-safe)
  (:vop-var vop)
  (:generator 3
     (emit-single-step-test)
     (inst jmp :eq DONE)
     (inst break single-step-before-trap)
     DONE
     (note-this-location vop :step-before-vop)))