src/code/dyncount.lisp

   1 ;;;; runtime support for dynamic VOP statistics collection
   2
   3 ;;;; This software is part of the SBCL system. See the README file for
   4 ;;;; more information.
   5 ;;;;
   6 ;;;; This software is derived from the CMU CL system, which was
   7 ;;;; written at Carnegie Mellon University and released into the
   8 ;;;; public domain. The software is in the public domain and is
   9 ;;;; provided with absolutely no warranty. See the COPYING and CREDITS
  10 ;;;; files for more information.
  11
  12 (in-package "SB!DYNCOUNT")
  13
  14 #|
  15 comments from CMU CL:
  16   Make sure multi-cycle instruction costs are plausible.
  17   VOP classification.
  18     Make tables of %cost for benchmark X class.
  19     Could be represented as a sort of bar chart.
  20 |#
  21
  22 (eval-when (:compile-toplevel)
  23   (when *collect-dynamic-statistics*
  24     (error "Compiling this file with dynamic stat collection turned on would ~
  25     be a very bad idea.")))
  26 \f
  27 ;;;; hash utilities
  28
  29 (defun make-hash-table-like (table)
  30   #!+sb-doc
  31   "Make a hash-table with the same test as table."
  32   (declare (type hash-table table))
  33   (make-hash-table :test (sb!impl::hash-table-kind table)))
  34
  35 (defun hash-difference (table1 table2)
  36   #!+sb-doc
  37   "Return a hash-table containing only the entries in Table1 whose key is not
  38    also a key in Table2." (declare (type hash-table table1 table2))
  39   (let ((res (make-hash-table-like table1)))
  40     (dohash (k v table1)
  41       (unless (nth-value 1 (gethash k table2))
  42         (setf (gethash k res) v)))
  43     res))
  44
  45 (defun hash-list (table)
  46   #!+sb-doc
  47   "Return a list of the values in Table."
  48   (declare (type hash-table table))
  49   (collect ((res))
  50     (dohash (k v table)
  51       (declare (ignore k))
  52       (res v))
  53     (res)))
  54
  55 ;;; Read (or write) a hashtable from (or to) a file.
  56 (defun read-hash-table (file)
  57   (with-open-file (s file :direction :input)
  58     (dotimes (i 3)
  59       (format t "~%; ~A" (read-line s)))
  60     (let* ((eof '(nil))
  61            (test (read s))
  62            (reader (read s))
  63            (res (make-hash-table :test test)))
  64       (read s); Discard writer...
  65       (loop
  66         (let ((key (read s nil eof)))
  67           (when (eq key eof) (return))
  68           (setf (gethash key res)
  69                 (funcall reader s key))))
  70       res)))
  71 (defun write-hash-table (table file &key
  72                                (comment (format nil "Contents of ~S" table))
  73                                (reader 'read) (writer 'prin1) (test 'equal))
  74   (with-open-file (s file :direction :output :if-exists :new-version)
  75     (with-standard-io-syntax
  76       (let ((*print-readably* nil))
  77         (format s
  78                 "~A~%~A version ~A on ~A~%"
  79                 comment
  80                 (lisp-implementation-type)
  81                 (lisp-implementation-version)
  82                 (machine-instance))
  83         (format-universal-time s (get-universal-time))
  84         (terpri s)
  85         (format s "~S ~S ~S~%" test reader writer)
  86         (dohash (k v table)
  87           (prin1 k s)
  88           (write-char #\space s)
  89           (funcall writer v s)
  90           (terpri s)))))
  91   table)
  92 \f
  93 ;;;; info accumulation
  94
  95 ;;; Used to accumulate info about the usage of a single VOP. Cost and count
  96 ;;; are kept as double-floats, which lets us get more bits and avoid annoying
  97 ;;; overflows.
  98 (deftype count-vector () '(simple-array double-float (2)))
  99 (defstruct (vop-stats
 100             (:constructor %make-vop-stats (name))
 101             (:constructor make-vop-stats-key)
 102             (:copier nil))
 103   (name (missing-arg) :type simple-string)
 104   (data (make-array 2 :element-type 'double-float) :type count-vector))
 105
 106 (defmacro vop-stats-count (x) `(aref (vop-stats-data ,x) 0))
 107 (defmacro vop-stats-cost (x) `(aref (vop-stats-data ,x) 1))
 108
 109 (defun make-vop-stats (&key name count cost)
 110   (let ((res (%make-vop-stats name)))
 111     (setf (vop-stats-count res) count)
 112     (setf (vop-stats-cost res) cost)
 113     res))
 114
 115 #!-sb-fluid (declaim (freeze-type dyncount-info vop-stats))
 116
 117 ;;;    Add the Info into the cumulative result on the VOP name plist. We use
 118 ;;; plists so that we will touch minimal system code outside of this file
 119 ;;; (which may be compiled with profiling on.)
 120 (defun note-dyncount-info (info)
 121   (declare (type dyncount-info info) (inline get %put)
 122            (optimize (speed 2)))
 123   (let ((counts (dyncount-info-counts info))
 124         (vops (dyncount-info-vops info)))
 125     (dotimes (index (length counts))
 126       (declare (type index index))
 127       (let ((count (coerce (the (unsigned-byte 31)
 128                                 (aref counts index))
 129                            'double-float)))
 130         (when (minusp count)
 131           (warn "Oops: overflow.")
 132           (return-from note-dyncount-info nil))
 133         (unless (zerop count)
 134           (let* ((vop-info (svref vops index))
 135                  (length (length vop-info)))
 136             (declare (simple-vector vop-info))
 137             (do ((i 0 (+ i 4)))
 138                 ((>= i length))
 139               (declare (type index i))
 140               (let* ((name (svref vop-info i))
 141                      (entry (or (get name 'vop-stats)
 142                                 (setf (get name 'vop-stats)
 143                                       (%make-vop-stats (symbol-name name))))))
 144                 (incf (vop-stats-count entry)
 145                       (* (coerce (the index (svref vop-info (1+ i)))
 146                                  'double-float)
 147                          count))
 148                 (incf (vop-stats-cost entry)
 149                       (* (coerce (the index (svref vop-info (+ i 2)))
 150                                  'double-float)
 151                          count))))))))))
 152
 153 (defun clear-dyncount-info (info)
 154   (declare (type dyncount-info info))
 155   (declare (optimize (speed 3) (safety 0)))
 156   (let ((counts (dyncount-info-counts info)))
 157     (dotimes (i (length counts))
 158       (setf (aref counts i) 0))))
 159
 160 ;;; Clear any VOP-COUNTS properties and the counts vectors for all code
 161 ;;; objects. The latter loop must not call any random functions.
 162 (defun clear-vop-counts (&optional (spaces '(:dynamic)))
 163   #!+sb-doc
 164   "Clear all dynamic VOP counts for code objects in the specified spaces."
 165   (dohash (k v *backend-template-names*)
 166     (declare (ignore v))
 167     (remprop k 'vop-stats))
 168
 169   (locally
 170       (declare (optimize (speed 3) (safety 0))
 171                (inline sb!vm::map-allocated-objects))
 172     (without-gcing
 173       (dolist (space spaces)
 174         (sb!vm::map-allocated-objects
 175          (lambda (object type-code size)
 176            (declare (ignore type-code size))
 177            (when (dyncount-info-p object)
 178              (clear-dyncount-info object)))
 179          space)))))
 180
 181 ;;; Call NOTE-DYNCOUNT-INFO on all DYNCOUNT-INFO structure allocated in the
 182 ;;; specified spaces. Return a hashtable describing the counts. The initial
 183 ;;; loop must avoid calling any functions outside this file to prevent adding
 184 ;;; noise to the data, since other files may be compiled with profiling.
 185 (defun get-vop-counts (&optional (spaces '(:dynamic)) &key (clear nil))
 186   #!+sb-doc
 187   "Return a hash-table mapping string VOP names to VOP-STATS structures
 188    describing the VOPs executed. If clear is true, then reset all counts to
 189    zero as a side effect."
 190   (locally
 191       (declare (optimize (speed 3) (safety 0))
 192                (inline sb!vm::map-allocated-objects))
 193     (without-gcing
 194       (dolist (space spaces)
 195         (sb!vm::map-allocated-objects
 196          (lambda (object type-code size)
 197            (declare (ignore type-code size))
 198            (when (dyncount-info-p object)
 199              (note-dyncount-info object)
 200              (when clear
 201                (clear-dyncount-info object))))
 202          space))))
 203
 204   (let ((counts (make-hash-table :test 'equal)))
 205     (dohash (k v *backend-template-names*)
 206       (declare (ignore v))
 207       (let ((stats (get k 'vop-stats)))
 208         (when stats
 209           (setf (gethash (symbol-name k) counts) stats)
 210           (when clear
 211             (remprop k 'vop-stats)))))
 212     counts))
 213
 214 ;;; Return the DYNCOUNT-INFO for FUNCTION.
 215 (defun find-info-for (function)
 216   (declare (type function function))
 217   (let* ((function (%primitive closure-fun function))
 218          (component (sb!di::fun-code-header function)))
 219     (do ((end (get-header-data component))
 220          (i sb!vm:code-constants-offset (1+ i)))
 221         ((= end i))
 222       (let ((constant (code-header-ref component i)))
 223         (when (dyncount-info-p constant)
 224           (return constant))))))
 225
 226 (defun vop-counts-apply (function args &key (spaces '(:dynamic)) by-space)
 227   #!+sb-doc
 228   "Apply Function to Args, collecting dynamic statistics on the running.
 229    Spaces are the spaces to scan for counts. If By-Space is true, we return a
 230    list of result tables, instead of a single table. In this case, specify
 231    :READ-ONLY first."
 232   (clear-vop-counts spaces)
 233   (apply function args)
 234   (if by-space
 235       (mapcar (lambda (space)
 236                 (get-vop-counts (list space) :clear t))
 237               spaces)
 238       (get-vop-counts spaces)))
 239 \f
 240 ;;;; adjustments
 241
 242 (defun get-vop-costs ()
 243   #!+sb-doc
 244   "Return a hash-table mapping string VOP names to the cost recorded in the
 245    generator for all VOPs which are also the names of assembly routines."
 246   (let ((res (make-hash-table :test 'equal)))
 247      (dohash (name v *assembler-routines*)
 248        (declare (ignore v))
 249        (let ((vop (gethash name *backend-template-names*)))
 250          (when vop
 251            (setf (gethash (symbol-name name) res)
 252                  (template-cost (template-or-lose name))))))
 253     res))
 254
 255 (defvar *native-costs* (get-vop-costs)
 256   #!+sb-doc
 257   "Costs of assember routines on this machine.")
 258 \f
 259 ;;;; classification
 260
 261 (defparameter *basic-classes*
 262   '(("Integer multiplication"
 263      "*/FIXNUM" "*/SIGNED" "*/UNSIGNED" "SIGNED-*" "FIXNUM-*" "GENERIC-*")
 264     ("Integer division" "TRUNCATE")
 265     ("Generic arithmetic" "GENERIC" "TWO-ARG")
 266     ("Inline EQL" "EQL")
 267     ("Inline compare less/greater" "</" ">/" "<-C/" ">-C/")
 268     ("Inline arith" "*/" "//" "+/" "-/" "NEGATE" "ABS" "+-C" "--C")
 269     ("Inline logic" "-ASH" "$ASH" "LOG")
 270     ("CAR/CDR" "CAR" "CDR")
 271     ("Array type test" "ARRAYP" "VECTORP" "ARRAY-HEADER-P")
 272     ;; FIXME: STRUCTUREP? This looks somewhat stale..
 273     ("Simple type predicate" "STRUCTUREP" "LISTP" "FIXNUMP")
 274     ("Simple type check" "CHECK-LIST" "CHECK-FIXNUM" "CHECK-STRUCTURE")
 275     ("Array bounds check" "CHECK-BOUND")
 276     ("Complex type check" "$CHECK-" "COERCE-TO-FUN")
 277     ("Special read" "SYMBOL-VALUE")
 278     ("Special bind" "BIND$")
 279     ("Tagging" "MOVE-FROM")
 280     ("Untagging" "MOVE-TO" "MAKE-FIXNUM")
 281     ("Move" "MOVE")
 282     ("Non-local exit" "CATCH" "THROW" "DYNAMIC-STATE" "NLX" "UNWIND")
 283     ("Array write" "DATA-VECTOR-SET" "$SET-RAW-BITS$")
 284     ("Array read" "DATA-VECTOR-REF" "$RAW-BITS$" "VECTOR-LENGTH"
 285      "LENGTH/SIMPLE" "ARRAY-HEADER")
 286     ("List/string utility" "LENGTH/LIST" "SXHASH" "BIT-BASH" "$LENGTH$")
 287     ("Alien operations" "SAP" "ALLOC-NUMBER-STACK" "$CALL-OUT$")
 288     ("Function call/return" "CALL" "RETURN" "ALLOCATE-FRAME"
 289      "COPY-MORE-ARG" "LISTIFY-REST-ARG" "VERIFY-ARG-COUNT")
 290     ("Allocation" "MAKE-" "ALLOC" "$CONS$" "$LIST$" "$LIST*$")
 291     ("Float conversion" "%SINGLE-FLOAT" "%DOUBLE-FLOAT" "-BITS$")
 292     ("Complex type predicate" "P$")))
 293
 294 ;;;    Return true if Name patches a specified pattern. Pattern is a string
 295 ;;; (or symbol) or a list of strings (or symbols). If any specified string
 296 ;;; appears as a substring of name, the pattern is matched. #\$'s are wapped
 297 ;;; around name, allowing the use of $ to force a match at the beginning or
 298 ;;; end.
 299 (defun matches-pattern (name pattern)
 300   (declare (simple-string name))
 301   (let ((name (concatenate 'string "$" name "$")))
 302     (dolist (pat (if (listp pattern) pattern (list pattern)) nil)
 303       (when (search (the simple-string (string pat))
 304                     name :test #'char=)
 305         (return t)))))
 306
 307 ;;; Utilities for debugging classification rules. FIND-MATCHES returns a
 308 ;;; list of all the VOP names in Table that match Pattern. WHAT-CLASS returns
 309 ;;; the class that NAME would be placed in.
 310 (defun find-matches (table pattern)
 311   (collect ((res))
 312     (dohash (key value table)
 313       (declare (ignore value))
 314       (when (matches-pattern key pattern) (res key)))
 315     (res)))
 316 (defun what-class (name classes)
 317   (dolist (class classes nil)
 318     (when (matches-pattern name (rest class)) (return (first class)))))
 319
 320 ;;; Given a VOP-STATS hash-table, return a new one with VOPs in the same
 321 ;;; class merged into a single entry for that class. The classes are
 322 ;;; represented as a list of lists: (class-name pattern*). Each pattern is a
 323 ;;; string (or symbol) that can appear as a subsequence of the VOP name. A VOP
 324 ;;; is placed in the first class that it matches, or is left alone if it
 325 ;;; matches no class.
 326 (defun classify-costs (table classes)
 327   (let ((res (make-hash-table-like table)))
 328     (dohash (key value table)
 329       (let ((class (dolist (class classes nil)
 330                      (when (matches-pattern key (rest class))
 331                        (return (first class))))))
 332         (if class
 333             (let ((found (or (gethash class res)
 334                              (setf (gethash class res)
 335                                    (%make-vop-stats class)))))
 336               (incf (vop-stats-count found) (vop-stats-count value))
 337               (incf (vop-stats-cost found) (vop-stats-cost value)))
 338             (setf (gethash key res) value))))
 339     res))
 340 \f
 341 ;;;; analysis
 342
 343 ;;; Sum the count and costs.
 344 (defun cost-summary (table)
 345   (let ((total-count 0d0)
 346         (total-cost 0d0))
 347     (dohash (k v table)
 348       (declare (ignore k))
 349       (incf total-count (vop-stats-count v))
 350       (incf total-cost (vop-stats-cost v)))
 351     (values total-count total-cost)))
 352
 353 ;;; Return a hashtable of DYNCOUNT-INFO structures, with cost adjustments
 354 ;;; according to the Costs table. Any VOPs in the list IGNORE are ignored.
 355 (defun compensate-costs (table costs &optional ignore)
 356   (let ((res (make-hash-table-like table)))
 357     (dohash (key value table)
 358       (unless (or (string= key "COUNT-ME")
 359                   (member key ignore :test #'string=))
 360         (let ((cost (gethash key costs)))
 361           (if cost
 362               (let* ((count (vop-stats-count value))
 363                      (sum (+ (* cost count)
 364                              (vop-stats-cost value))))
 365                 (setf (gethash key res)
 366                       (make-vop-stats :name key :count count :cost sum)))
 367               (setf (gethash key res) value)))))
 368     res))
 369
 370 ;;; Take two tables of vop-stats and return a table of entries where the
 371 ;;; entries have been compared. The counts are normalized to Compared. The
 372 ;;; costs are the difference of the costs adjusted by the difference in counts:
 373 ;;; the cost for Original is modified to correspond to the count in Compared.
 374 (defun compare-stats (original compared)
 375   (declare (type hash-table original compared))
 376   (let ((res (make-hash-table-like original)))
 377     (dohash (k cv compared)
 378       (let ((ov (gethash k original)))
 379         (when ov
 380           (let ((norm-cnt (/ (vop-stats-count ov) (vop-stats-count cv))))
 381             (setf (gethash k res)
 382                   (make-vop-stats
 383                    :name k
 384                    :count norm-cnt
 385                    :cost (- (/ (vop-stats-cost ov) norm-cnt)
 386                             (vop-stats-cost cv))))))))
 387     res))
 388
 389 (defun combine-stats (&rest tables)
 390   #!+sb-doc
 391   "Sum the VOP stats for the specified tables, returning a new table with the
 392    combined results."
 393   (let ((res (make-hash-table-like (first tables))))
 394     (dolist (table tables)
 395       (dohash (k v table)
 396         (let ((found (or (gethash k res)
 397                          (setf (gethash k res) (%make-vop-stats k)))))
 398           (incf (vop-stats-count found) (vop-stats-count v))
 399           (incf (vop-stats-cost found) (vop-stats-cost v)))))
 400     res))
 401 \f
 402 ;;;; report generation
 403
 404 (defun sort-result (table by)
 405   (sort (hash-list table) #'>
 406         :key (lambda (x)
 407                (abs (ecase by
 408                       (:count (vop-stats-count x))
 409                       (:cost (vop-stats-cost x)))))))
 410
 411 ;;; Report about VOPs in the list of stats structures.
 412 (defun entry-report (entries cut-off compensated compare total-cost)
 413   (let ((counter (if (and cut-off (> (length entries) cut-off))
 414                      cut-off
 415                      most-positive-fixnum)))
 416   (dolist (entry entries)
 417     (let* ((cost (vop-stats-cost entry))
 418            (name (vop-stats-name entry))
 419            (entry-count (vop-stats-count entry))
 420            (comp-entry (if compare (gethash name compare) entry))
 421            (count (vop-stats-count comp-entry)))
 422       (format t "~30<~A~>: ~:[~13:D~;~13,2F~] ~9,2F  ~5,2,2F%~%"
 423               (vop-stats-name entry)
 424               compare
 425               (if compare entry-count (round entry-count))
 426               (/ cost count)
 427               (/ (if compare
 428                      (- (vop-stats-cost (gethash name compensated))
 429                         (vop-stats-cost comp-entry))
 430                      cost)
 431                  total-cost))
 432       (when (zerop (decf counter))
 433         (format t "[End of top ~W]~%" cut-off))))))
 434
 435 ;;; Divide SORTED into two lists, the first CUT-OFF elements long. Any VOP
 436 ;;; names that match one of the report strings are moved into the REPORT list
 437 ;;; even if they would otherwise fall below the CUT-OFF.
 438 (defun find-cut-off (sorted cut-off report)
 439   (if (or (not cut-off) (<= (length sorted) cut-off))
 440       (values sorted ())
 441       (let ((not-cut (subseq sorted 0 cut-off)))
 442         (collect ((select)
 443                   (reject))
 444           (dolist (el (nthcdr cut-off sorted))
 445             (let ((name (vop-stats-name el)))
 446               (if (matches-pattern name report)
 447                   (select el)
 448                   (reject el))))
 449           (values (append not-cut (select)) (reject))))))
 450
 451 ;;; Display information about entries that were not displayed due to the
 452 ;;; cut-off. Note: if compare, we find the total cost delta and the geometric
 453 ;;; mean of the normalized counts.
 454 (defun cut-off-report (other compare total-cost)
 455   (let ((rest-cost 0d0)
 456         (rest-count 0d0)
 457         (rest-entry-count (if compare 1d0 0d0)))
 458     (dolist (entry other)
 459       (incf rest-cost (vop-stats-cost entry))
 460       (incf rest-count
 461             (vop-stats-count
 462              (if compare
 463                  (gethash (vop-stats-name entry) compare)
 464                  entry)))
 465       (if compare
 466           (setq rest-entry-count
 467                 (* rest-entry-count (vop-stats-count entry)))
 468           (incf rest-entry-count (vop-stats-count entry))))
 469
 470     (let ((count (if compare
 471                      (expt rest-entry-count
 472                            (/ (coerce (length other) 'double-float)))
 473                      (round rest-entry-count))))
 474       (format t "~30<Other~>: ~:[~13:D~;~13,2F~] ~9,2F  ~@[~5,2,2F%~]~%"
 475               compare count
 476               (/ rest-cost rest-count)
 477               (unless compare
 478                 (/ rest-cost total-cost))))))
 479
 480 ;;; Report summary information about the difference between the comparison
 481 ;;; and base data sets.
 482 (defun compare-report (total-count total-cost compare-total-count
 483                                    compare-total-cost compensated compare)
 484   (format t "~30<Relative total~>: ~13,2F ~9,2F~%"
 485           (/ total-count compare-total-count)
 486           (/ total-cost compare-total-cost))
 487   (flet ((frob (a b sign wot)
 488            (multiple-value-bind (cost count)
 489                (cost-summary (hash-difference a b))
 490              (unless (zerop count)
 491                (format t "~30<~A~>: ~13:D ~9,2F  ~5,2,2F%~%"
 492                        wot (* sign (round count))
 493                        (* sign (/ cost count))
 494                        (* sign (/ cost compare-total-cost)))))))
 495     (frob compensated compare 1 "Not in comparison")
 496     (frob compare compensated -1 "Only in comparison"))
 497   (format t "~30<Comparison total~>: ~13,2E ~9,2E~%"
 498           compare-total-count compare-total-cost))
 499
 500 ;;; The fraction of system time that we guess happened during GC.
 501 (defparameter *gc-system-fraction* 2/3)
 502
 503 ;;; Estimate CPI from CPU time and cycles accounted in profiling information.
 504 (defun find-cpi (total-cost user system gc clock)
 505   (let ((adj-time (if (zerop gc)
 506                       user
 507                       (- user (- gc (* system *gc-system-fraction*))))))
 508     (/ (* adj-time clock) total-cost)))
 509
 510 ;;; Generate a report from the specified table.
 511 (defun generate-report (table &key (cut-off 15) (sort-by :cost)
 512                               (costs *native-costs*)
 513                               ((:compare uncomp-compare))
 514                               (compare-costs costs)
 515                               ignore report
 516                               (classes *basic-classes*)
 517                               user (system 0d0) (gc 0d0)
 518                               (clock 25d6))
 519   (let* ((compensated
 520           (classify-costs
 521            (if costs
 522                (compensate-costs table costs ignore)
 523                table)
 524            classes))
 525          (compare
 526           (when uncomp-compare
 527             (classify-costs
 528              (if compare-costs
 529                  (compensate-costs uncomp-compare compare-costs ignore)
 530                  uncomp-compare)
 531              classes)))
 532          (compared (if compare
 533                        (compare-stats compensated compare)
 534                        compensated)))
 535     (multiple-value-bind (total-count total-cost) (cost-summary compensated)
 536       (multiple-value-bind (compare-total-count compare-total-cost)
 537           (when compare (cost-summary compare))
 538         (format t "~2&~30<Vop~>  ~13<Count~> ~9<Cost~>  ~6:@<Percent~>~%")
 539         (let ((sorted (sort-result compared sort-by))
 540               (base-total (if compare compare-total-cost total-cost)))
 541           (multiple-value-bind (report other)
 542               (find-cut-off sorted cut-off report)
 543             (entry-report report cut-off compensated compare base-total)
 544             (when other
 545               (cut-off-report other compare base-total))))
 546
 547         (when compare
 548           (compare-report total-count total-cost compare-total-count
 549                           compare-total-cost compensated compare))
 550
 551         (format t "~30<Total~>: ~13,2E ~9,2E~%" total-count total-cost)
 552         (when user
 553           (format t "~%Cycles per instruction = ~,2F~%"
 554                   (find-cpi total-cost user system gc clock))))))
 555   (values))
 556
 557 ;;; Read & write VOP stats using hash IO utility.
 558 (defun stats-reader (stream key)
 559   (make-vop-stats :name key :count (read stream) :cost (read stream)))
 560 (defun stats-writer (object stream)
 561   (format stream "~S ~S" (vop-stats-count object) (vop-stats-cost object)))