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master 09bfb12 1/4: * lisp/emacs-lisp/byte-opt.el (byte-optimize-lapcode


From: Stefan Monnier
Subject: master 09bfb12 1/4: * lisp/emacs-lisp/byte-opt.el (byte-optimize-lapcode): Re-indent
Date: Wed, 20 Jan 2021 14:13:27 -0500 (EST)

branch: master
commit 09bfb12edc57ace138090861e335366d8f1cc4b2
Author: Stefan Monnier <monnier@iro.umontreal.ca>
Commit: Stefan Monnier <monnier@iro.umontreal.ca>

    * lisp/emacs-lisp/byte-opt.el (byte-optimize-lapcode): Re-indent
---
 lisp/emacs-lisp/byte-opt.el | 914 ++++++++++++++++++++++----------------------
 1 file changed, 457 insertions(+), 457 deletions(-)

diff --git a/lisp/emacs-lisp/byte-opt.el b/lisp/emacs-lisp/byte-opt.el
index f29f85b..6d1f417 100644
--- a/lisp/emacs-lisp/byte-opt.el
+++ b/lisp/emacs-lisp/byte-opt.el
@@ -1561,467 +1561,467 @@ If FOR-EFFECT is non-nil, the return value is assumed 
to be of no importance."
        ;; You may notice that sequences like "dup varset discard" are
        ;; optimized but sequences like "dup varset TAG1: discard" are not.
        ;; You may be tempted to change this; resist that temptation.
-       (cond ;;
-             ;; <side-effect-free> pop -->  <deleted>
-             ;;  ...including:
-             ;; const-X pop   -->  <deleted>
-             ;; varref-X pop  -->  <deleted>
-             ;; dup pop       -->  <deleted>
-             ;;
-             ((and (eq 'byte-discard (car lap1))
-                   (memq (car lap0) side-effect-free))
-              (setq keep-going t)
-              (setq tmp (aref byte-stack+-info (symbol-value (car lap0))))
-              (setq rest (cdr rest))
-              (cond ((= tmp 1)
-                     (byte-compile-log-lap
-                      "  %s discard\t-->\t<deleted>" lap0)
-                     (setq lap (delq lap0 (delq lap1 lap))))
-                    ((= tmp 0)
-                     (byte-compile-log-lap
-                      "  %s discard\t-->\t<deleted> discard" lap0)
-                     (setq lap (delq lap0 lap)))
-                    ((= tmp -1)
-                     (byte-compile-log-lap
-                      "  %s discard\t-->\tdiscard discard" lap0)
-                     (setcar lap0 'byte-discard)
-                     (setcdr lap0 0))
-                    ((error "Optimizer error: too much on the stack"))))
-             ;;
-             ;; goto*-X X:  -->  X:
-             ;;
-             ((and (memq (car lap0) byte-goto-ops)
-                   (eq (cdr lap0) lap1))
-              (cond ((eq (car lap0) 'byte-goto)
-                     (setq lap (delq lap0 lap))
-                     (setq tmp "<deleted>"))
-                    ((memq (car lap0) byte-goto-always-pop-ops)
-                     (setcar lap0 (setq tmp 'byte-discard))
-                     (setcdr lap0 0))
-                    ((error "Depth conflict at tag %d" (nth 2 lap0))))
-              (and (memq byte-optimize-log '(t byte))
-                   (byte-compile-log "  (goto %s) %s:\t-->\t%s %s:"
-                                     (nth 1 lap1) (nth 1 lap1)
-                                     tmp (nth 1 lap1)))
-              (setq keep-going t))
-             ;;
-             ;; varset-X varref-X  -->  dup varset-X
-             ;; varbind-X varref-X  -->  dup varbind-X
-             ;; const/dup varset-X varref-X --> const/dup varset-X const/dup
-             ;; const/dup varbind-X varref-X --> const/dup varbind-X const/dup
-             ;; The latter two can enable other optimizations.
-             ;;
-              ;; For lexical variables, we could do the same
-              ;;   stack-set-X+1 stack-ref-X  -->  dup stack-set-X+2
-              ;; but this is a very minor gain, since dup is stack-ref-0,
-              ;; i.e. it's only better if X>5, and even then it comes
-              ;; at the cost of an extra stack slot.  Let's not bother.
-             ((and (eq 'byte-varref (car lap2))
-                    (eq (cdr lap1) (cdr lap2))
-                    (memq (car lap1) '(byte-varset byte-varbind)))
-              (if (and (setq tmp (memq (car (cdr lap2)) byte-boolean-vars))
-                       (not (eq (car lap0) 'byte-constant)))
-                  nil
-                (setq keep-going t)
-                 (if (memq (car lap0) '(byte-constant byte-dup))
-                     (progn
-                       (setq tmp (if (or (not tmp)
-                                         (macroexp--const-symbol-p
-                                          (car (cdr lap0))))
-                                     (cdr lap0)
-                                   (byte-compile-get-constant t)))
-                      (byte-compile-log-lap "  %s %s %s\t-->\t%s %s %s"
-                                            lap0 lap1 lap2 lap0 lap1
-                                            (cons (car lap0) tmp))
-                      (setcar lap2 (car lap0))
-                      (setcdr lap2 tmp))
-                  (byte-compile-log-lap "  %s %s\t-->\tdup %s" lap1 lap2 lap1)
-                  (setcar lap2 (car lap1))
-                  (setcar lap1 'byte-dup)
-                  (setcdr lap1 0)
-                  ;; The stack depth gets locally increased, so we will
-                  ;; increase maxdepth in case depth = maxdepth here.
-                  ;; This can cause the third argument to byte-code to
-                  ;; be larger than necessary.
-                  (setq add-depth 1))))
-             ;;
-             ;; dup varset-X discard  -->  varset-X
-             ;; dup varbind-X discard  -->  varbind-X
-              ;; dup stack-set-X discard  -->  stack-set-X-1
-             ;; (the varbind variant can emerge from other optimizations)
-             ;;
-             ((and (eq 'byte-dup (car lap0))
-                   (eq 'byte-discard (car lap2))
-                   (memq (car lap1) '(byte-varset byte-varbind
-                                       byte-stack-set)))
-              (byte-compile-log-lap "  dup %s discard\t-->\t%s" lap1 lap1)
-              (setq keep-going t
-                    rest (cdr rest))
-               (if (eq 'byte-stack-set (car lap1)) (cl-decf (cdr lap1)))
-              (setq lap (delq lap0 (delq lap2 lap))))
-             ;;
-             ;; not goto-X-if-nil              -->  goto-X-if-non-nil
-             ;; not goto-X-if-non-nil          -->  goto-X-if-nil
-             ;;
-             ;; it is wrong to do the same thing for the -else-pop variants.
-             ;;
-             ((and (eq 'byte-not (car lap0))
-                   (memq (car lap1) '(byte-goto-if-nil byte-goto-if-not-nil)))
-              (byte-compile-log-lap "  not %s\t-->\t%s"
-                                    lap1
-                                    (cons
-                                     (if (eq (car lap1) 'byte-goto-if-nil)
-                                         'byte-goto-if-not-nil
-                                       'byte-goto-if-nil)
-                                     (cdr lap1)))
-              (setcar lap1 (if (eq (car lap1) 'byte-goto-if-nil)
-                               'byte-goto-if-not-nil
-                               'byte-goto-if-nil))
-              (setq lap (delq lap0 lap))
-              (setq keep-going t))
-             ;;
-             ;; goto-X-if-nil     goto-Y X:  -->  goto-Y-if-non-nil X:
-             ;; goto-X-if-non-nil goto-Y X:  -->  goto-Y-if-nil     X:
-             ;;
-             ;; it is wrong to do the same thing for the -else-pop variants.
-             ;;
-             ((and (memq (car lap0)
-                          '(byte-goto-if-nil byte-goto-if-not-nil))    ; gotoX
-                   (eq 'byte-goto (car lap1))                  ; gotoY
-                   (eq (cdr lap0) lap2))                       ; TAG X
-              (let ((inverse (if (eq 'byte-goto-if-nil (car lap0))
-                                 'byte-goto-if-not-nil 'byte-goto-if-nil)))
-                (byte-compile-log-lap "  %s %s %s:\t-->\t%s %s:"
-                                      lap0 lap1 lap2
-                                      (cons inverse (cdr lap1)) lap2)
-                (setq lap (delq lap0 lap))
-                (setcar lap1 inverse)
-                (setq keep-going t)))
-             ;;
-             ;; const goto-if-* --> whatever
-             ;;
-             ((and (eq 'byte-constant (car lap0))
-                   (memq (car lap1) byte-conditional-ops)
-                    ;; If the `byte-constant's cdr is not a cons cell, it has
-                    ;; to be an index into the constant pool); even though
-                    ;; it'll be a constant, that constant is not known yet
-                    ;; (it's typically a free variable of a closure, so will
-                    ;; only be known when the closure will be built at
-                    ;; run-time).
-                    (consp (cdr lap0)))
-              (cond ((if (memq (car lap1) '(byte-goto-if-nil
-                                             byte-goto-if-nil-else-pop))
-                          (car (cdr lap0))
-                        (not (car (cdr lap0))))
-                     (byte-compile-log-lap "  %s %s\t-->\t<deleted>"
-                                           lap0 lap1)
-                     (setq rest (cdr rest)
-                           lap (delq lap0 (delq lap1 lap))))
-                    (t
-                     (byte-compile-log-lap "  %s %s\t-->\t%s"
-                                           lap0 lap1
-                                           (cons 'byte-goto (cdr lap1)))
-                     (when (memq (car lap1) byte-goto-always-pop-ops)
-                       (setq lap (delq lap0 lap)))
-                     (setcar lap1 'byte-goto)))
-               (setq keep-going t))
-             ;;
-             ;; varref-X varref-X  -->  varref-X dup
-             ;; varref-X [dup ...] varref-X  -->  varref-X [dup ...] dup
-             ;; stackref-X [dup ...] stackref-X+N --> stackref-X [dup ...] dup
-             ;; We don't optimize the const-X variations on this here,
-             ;; because that would inhibit some goto optimizations; we
-             ;; optimize the const-X case after all other optimizations.
-             ;;
-             ((and (memq (car lap0) '(byte-varref byte-stack-ref))
-                   (progn
-                     (setq tmp (cdr rest))
-                      (setq tmp2 0)
-                     (while (eq (car (car tmp)) 'byte-dup)
-                       (setq tmp2 (1+ tmp2))
-                        (setq tmp (cdr tmp)))
-                     t)
-                   (eq (if (eq 'byte-stack-ref (car lap0))
-                            (+ tmp2 1 (cdr lap0))
-                          (cdr lap0))
-                        (cdr (car tmp)))
-                   (eq (car lap0) (car (car tmp))))
-              (if (memq byte-optimize-log '(t byte))
-                  (let ((str ""))
-                    (setq tmp2 (cdr rest))
-                    (while (not (eq tmp tmp2))
-                      (setq tmp2 (cdr tmp2)
-                            str (concat str " dup")))
-                    (byte-compile-log-lap "  %s%s %s\t-->\t%s%s dup"
-                                          lap0 str lap0 lap0 str)))
-              (setq keep-going t)
-              (setcar (car tmp) 'byte-dup)
-              (setcdr (car tmp) 0)
-              (setq rest tmp))
-             ;;
-             ;; TAG1: TAG2: --> TAG1: <deleted>
-             ;; (and other references to TAG2 are replaced with TAG1)
-             ;;
-             ((and (eq (car lap0) 'TAG)
-                   (eq (car lap1) 'TAG))
-              (and (memq byte-optimize-log '(t byte))
-                   (byte-compile-log "  adjacent tags %d and %d merged"
-                                     (nth 1 lap1) (nth 1 lap0)))
-              (setq tmp3 lap)
-              (while (setq tmp2 (rassq lap0 tmp3))
-                (setcdr tmp2 lap1)
-                (setq tmp3 (cdr (memq tmp2 tmp3))))
-              (setq lap (delq lap0 lap)
-                    keep-going t)
-               ;; replace references to tag in jump tables, if any
-               (dolist (table byte-compile-jump-tables)
-                   (maphash #'(lambda (value tag)
-                                (when (equal tag lap0)
-                                  (puthash value lap1 table)))
-                            table)))
-             ;;
-             ;; unused-TAG: --> <deleted>
-             ;;
-             ((and (eq 'TAG (car lap0))
-                   (not (rassq lap0 lap))
-                    ;; make sure this tag isn't used in a jump-table
-                    (cl-loop for table in byte-compile-jump-tables
-                             when (member lap0 (hash-table-values table))
-                             return nil finally return t))
-              (and (memq byte-optimize-log '(t byte))
-                   (byte-compile-log "  unused tag %d removed" (nth 1 lap0)))
-              (setq lap (delq lap0 lap)
-                    keep-going t))
-             ;;
-             ;; goto   ... --> goto   <delete until TAG or end>
-             ;; return ... --> return <delete until TAG or end>
-             ;; (unless a jump-table is being used, where deleting may affect
-              ;; other valid case bodies)
-              ;;
-             ((and (memq (car lap0) '(byte-goto byte-return))
-                   (not (memq (car lap1) '(TAG nil)))
-                    ;; FIXME: Instead of deferring simply when jump-tables are
-                    ;; being used, keep a list of tags used for switch tags and
-                    ;; use them instead (see `byte-compile-inline-lapcode').
-                    (not byte-compile-jump-tables))
-              (setq tmp rest)
-              (let ((i 0)
-                    (opt-p (memq byte-optimize-log '(t lap)))
-                    str deleted)
-                (while (and (setq tmp (cdr tmp))
-                            (not (eq 'TAG (car (car tmp)))))
-                  (if opt-p (setq deleted (cons (car tmp) deleted)
-                                  str (concat str " %s")
-                                  i (1+ i))))
-                (if opt-p
-                    (let ((tagstr
-                           (if (eq 'TAG (car (car tmp)))
-                               (format "%d:" (car (cdr (car tmp))))
-                             (or (car tmp) ""))))
-                      (if (< i 6)
-                          (apply 'byte-compile-log-lap-1
-                                 (concat "  %s" str
-                                         " %s\t-->\t%s <deleted> %s")
-                                 lap0
-                                 (nconc (nreverse deleted)
-                                        (list tagstr lap0 tagstr)))
-                        (byte-compile-log-lap
-                         "  %s <%d unreachable op%s> %s\t-->\t%s <deleted> %s"
-                         lap0 i (if (= i 1) "" "s")
-                         tagstr lap0 tagstr))))
-                (rplacd rest tmp))
-              (setq keep-going t))
-             ;;
-             ;; <safe-op> unbind --> unbind <safe-op>
-             ;; (this may enable other optimizations.)
-             ;;
-             ((and (eq 'byte-unbind (car lap1))
-                   (memq (car lap0) byte-after-unbind-ops))
-              (byte-compile-log-lap "  %s %s\t-->\t%s %s" lap0 lap1 lap1 lap0)
-              (setcar rest lap1)
-              (setcar (cdr rest) lap0)
-              (setq keep-going t))
-             ;;
-             ;; varbind-X unbind-N         -->  discard unbind-(N-1)
-             ;; save-excursion unbind-N    -->  unbind-(N-1)
-             ;; save-restriction unbind-N  -->  unbind-(N-1)
-             ;;
-             ((and (eq 'byte-unbind (car lap1))
-                   (memq (car lap0) '(byte-varbind byte-save-excursion
-                                      byte-save-restriction))
-                   (< 0 (cdr lap1)))
-              (if (zerop (setcdr lap1 (1- (cdr lap1))))
-                  (delq lap1 rest))
-              (if (eq (car lap0) 'byte-varbind)
-                  (setcar rest (cons 'byte-discard 0))
+       (cond
+        ;; <side-effect-free> pop -->  <deleted>
+        ;;  ...including:
+        ;; const-X pop   -->  <deleted>
+        ;; varref-X pop  -->  <deleted>
+        ;; dup pop       -->  <deleted>
+        ;;
+        ((and (eq 'byte-discard (car lap1))
+              (memq (car lap0) side-effect-free))
+         (setq keep-going t)
+         (setq tmp (aref byte-stack+-info (symbol-value (car lap0))))
+         (setq rest (cdr rest))
+         (cond ((= tmp 1)
+                (byte-compile-log-lap
+                 "  %s discard\t-->\t<deleted>" lap0)
+                (setq lap (delq lap0 (delq lap1 lap))))
+               ((= tmp 0)
+                (byte-compile-log-lap
+                 "  %s discard\t-->\t<deleted> discard" lap0)
                 (setq lap (delq lap0 lap)))
-              (byte-compile-log-lap "  %s %s\t-->\t%s %s"
-                lap0 (cons (car lap1) (1+ (cdr lap1)))
-                (if (eq (car lap0) 'byte-varbind)
-                    (car rest)
-                  (car (cdr rest)))
-                (if (and (/= 0 (cdr lap1))
-                         (eq (car lap0) 'byte-varbind))
-                    (car (cdr rest))
-                  ""))
-              (setq keep-going t))
-             ;;
-             ;; goto*-X ... X: goto-Y  --> goto*-Y
-             ;; goto-X ...  X: return  --> return
-             ;;
-             ((and (memq (car lap0) byte-goto-ops)
-                   (memq (car (setq tmp (nth 1 (memq (cdr lap0) lap))))
-                         '(byte-goto byte-return)))
-              (cond ((and (not (eq tmp lap0))
-                          (or (eq (car lap0) 'byte-goto)
-                              (eq (car tmp) 'byte-goto)))
-                     (byte-compile-log-lap "  %s [%s]\t-->\t%s"
-                                           (car lap0) tmp tmp)
-                     (if (eq (car tmp) 'byte-return)
-                         (setcar lap0 'byte-return))
-                     (setcdr lap0 (cdr tmp))
-                     (setq keep-going t))))
-             ;;
-             ;; goto-*-else-pop X ... X: goto-if-* --> whatever
-             ;; goto-*-else-pop X ... X: discard --> whatever
-             ;;
-             ((and (memq (car lap0) '(byte-goto-if-nil-else-pop
-                                      byte-goto-if-not-nil-else-pop))
-                   (memq (car (car (setq tmp (cdr (memq (cdr lap0) lap)))))
-                         (eval-when-compile
-                          (cons 'byte-discard byte-conditional-ops)))
-                   (not (eq lap0 (car tmp))))
-              (setq tmp2 (car tmp))
-              (setq tmp3 (assq (car lap0) '((byte-goto-if-nil-else-pop
-                                             byte-goto-if-nil)
-                                            (byte-goto-if-not-nil-else-pop
-                                             byte-goto-if-not-nil))))
-              (if (memq (car tmp2) tmp3)
-                  (progn (setcar lap0 (car tmp2))
-                         (setcdr lap0 (cdr tmp2))
-                         (byte-compile-log-lap "  %s-else-pop [%s]\t-->\t%s"
-                                               (car lap0) tmp2 lap0))
-                ;; Get rid of the -else-pop's and jump one step further.
+               ((= tmp -1)
+                (byte-compile-log-lap
+                 "  %s discard\t-->\tdiscard discard" lap0)
+                (setcar lap0 'byte-discard)
+                (setcdr lap0 0))
+               ((error "Optimizer error: too much on the stack"))))
+        ;;
+        ;; goto*-X X:  -->  X:
+        ;;
+        ((and (memq (car lap0) byte-goto-ops)
+              (eq (cdr lap0) lap1))
+         (cond ((eq (car lap0) 'byte-goto)
+                (setq lap (delq lap0 lap))
+                (setq tmp "<deleted>"))
+               ((memq (car lap0) byte-goto-always-pop-ops)
+                (setcar lap0 (setq tmp 'byte-discard))
+                (setcdr lap0 0))
+               ((error "Depth conflict at tag %d" (nth 2 lap0))))
+         (and (memq byte-optimize-log '(t byte))
+              (byte-compile-log "  (goto %s) %s:\t-->\t%s %s:"
+                                (nth 1 lap1) (nth 1 lap1)
+                                tmp (nth 1 lap1)))
+         (setq keep-going t))
+        ;;
+        ;; varset-X varref-X  -->  dup varset-X
+        ;; varbind-X varref-X  -->  dup varbind-X
+        ;; const/dup varset-X varref-X --> const/dup varset-X const/dup
+        ;; const/dup varbind-X varref-X --> const/dup varbind-X const/dup
+        ;; The latter two can enable other optimizations.
+        ;;
+         ;; For lexical variables, we could do the same
+         ;;   stack-set-X+1 stack-ref-X  -->  dup stack-set-X+2
+         ;; but this is a very minor gain, since dup is stack-ref-0,
+         ;; i.e. it's only better if X>5, and even then it comes
+         ;; at the cost of an extra stack slot.  Let's not bother.
+        ((and (eq 'byte-varref (car lap2))
+               (eq (cdr lap1) (cdr lap2))
+               (memq (car lap1) '(byte-varset byte-varbind)))
+         (if (and (setq tmp (memq (car (cdr lap2)) byte-boolean-vars))
+                  (not (eq (car lap0) 'byte-constant)))
+             nil
+           (setq keep-going t)
+            (if (memq (car lap0) '(byte-constant byte-dup))
+                (progn
+                  (setq tmp (if (or (not tmp)
+                                    (macroexp--const-symbol-p
+                                     (car (cdr lap0))))
+                                (cdr lap0)
+                              (byte-compile-get-constant t)))
+                 (byte-compile-log-lap "  %s %s %s\t-->\t%s %s %s"
+                                       lap0 lap1 lap2 lap0 lap1
+                                       (cons (car lap0) tmp))
+                 (setcar lap2 (car lap0))
+                 (setcdr lap2 tmp))
+             (byte-compile-log-lap "  %s %s\t-->\tdup %s" lap1 lap2 lap1)
+             (setcar lap2 (car lap1))
+             (setcar lap1 'byte-dup)
+             (setcdr lap1 0)
+             ;; The stack depth gets locally increased, so we will
+             ;; increase maxdepth in case depth = maxdepth here.
+             ;; This can cause the third argument to byte-code to
+             ;; be larger than necessary.
+             (setq add-depth 1))))
+        ;;
+        ;; dup varset-X discard  -->  varset-X
+        ;; dup varbind-X discard  -->  varbind-X
+         ;; dup stack-set-X discard  -->  stack-set-X-1
+        ;; (the varbind variant can emerge from other optimizations)
+        ;;
+        ((and (eq 'byte-dup (car lap0))
+              (eq 'byte-discard (car lap2))
+              (memq (car lap1) '(byte-varset byte-varbind
+                                  byte-stack-set)))
+         (byte-compile-log-lap "  dup %s discard\t-->\t%s" lap1 lap1)
+         (setq keep-going t
+               rest (cdr rest))
+          (if (eq 'byte-stack-set (car lap1)) (cl-decf (cdr lap1)))
+         (setq lap (delq lap0 (delq lap2 lap))))
+        ;;
+        ;; not goto-X-if-nil              -->  goto-X-if-non-nil
+        ;; not goto-X-if-non-nil          -->  goto-X-if-nil
+        ;;
+        ;; it is wrong to do the same thing for the -else-pop variants.
+        ;;
+        ((and (eq 'byte-not (car lap0))
+              (memq (car lap1) '(byte-goto-if-nil byte-goto-if-not-nil)))
+         (byte-compile-log-lap "  not %s\t-->\t%s"
+                               lap1
+                               (cons
+                                (if (eq (car lap1) 'byte-goto-if-nil)
+                                    'byte-goto-if-not-nil
+                                  'byte-goto-if-nil)
+                                (cdr lap1)))
+         (setcar lap1 (if (eq (car lap1) 'byte-goto-if-nil)
+                          'byte-goto-if-not-nil
+                        'byte-goto-if-nil))
+         (setq lap (delq lap0 lap))
+         (setq keep-going t))
+        ;;
+        ;; goto-X-if-nil     goto-Y X:  -->  goto-Y-if-non-nil X:
+        ;; goto-X-if-non-nil goto-Y X:  -->  goto-Y-if-nil     X:
+        ;;
+        ;; it is wrong to do the same thing for the -else-pop variants.
+        ;;
+        ((and (memq (car lap0)
+                     '(byte-goto-if-nil byte-goto-if-not-nil)) ; gotoX
+              (eq 'byte-goto (car lap1))                      ; gotoY
+              (eq (cdr lap0) lap2))                           ; TAG X
+         (let ((inverse (if (eq 'byte-goto-if-nil (car lap0))
+                            'byte-goto-if-not-nil 'byte-goto-if-nil)))
+           (byte-compile-log-lap "  %s %s %s:\t-->\t%s %s:"
+                                 lap0 lap1 lap2
+                                 (cons inverse (cdr lap1)) lap2)
+           (setq lap (delq lap0 lap))
+           (setcar lap1 inverse)
+           (setq keep-going t)))
+        ;;
+        ;; const goto-if-* --> whatever
+        ;;
+        ((and (eq 'byte-constant (car lap0))
+              (memq (car lap1) byte-conditional-ops)
+               ;; If the `byte-constant's cdr is not a cons cell, it has
+               ;; to be an index into the constant pool); even though
+               ;; it'll be a constant, that constant is not known yet
+               ;; (it's typically a free variable of a closure, so will
+               ;; only be known when the closure will be built at
+               ;; run-time).
+               (consp (cdr lap0)))
+         (cond ((if (memq (car lap1) '(byte-goto-if-nil
+                                        byte-goto-if-nil-else-pop))
+                     (car (cdr lap0))
+                   (not (car (cdr lap0))))
+                (byte-compile-log-lap "  %s %s\t-->\t<deleted>"
+                                      lap0 lap1)
+                (setq rest (cdr rest)
+                      lap (delq lap0 (delq lap1 lap))))
+               (t
+                (byte-compile-log-lap "  %s %s\t-->\t%s"
+                                      lap0 lap1
+                                      (cons 'byte-goto (cdr lap1)))
+                (when (memq (car lap1) byte-goto-always-pop-ops)
+                  (setq lap (delq lap0 lap)))
+                (setcar lap1 'byte-goto)))
+          (setq keep-going t))
+        ;;
+        ;; varref-X varref-X  -->  varref-X dup
+        ;; varref-X [dup ...] varref-X  -->  varref-X [dup ...] dup
+        ;; stackref-X [dup ...] stackref-X+N --> stackref-X [dup ...] dup
+        ;; We don't optimize the const-X variations on this here,
+        ;; because that would inhibit some goto optimizations; we
+        ;; optimize the const-X case after all other optimizations.
+        ;;
+        ((and (memq (car lap0) '(byte-varref byte-stack-ref))
+              (progn
+                (setq tmp (cdr rest))
+                 (setq tmp2 0)
+                (while (eq (car (car tmp)) 'byte-dup)
+                  (setq tmp2 (1+ tmp2))
+                   (setq tmp (cdr tmp)))
+                t)
+              (eq (if (eq 'byte-stack-ref (car lap0))
+                       (+ tmp2 1 (cdr lap0))
+                     (cdr lap0))
+                   (cdr (car tmp)))
+              (eq (car lap0) (car (car tmp))))
+         (if (memq byte-optimize-log '(t byte))
+             (let ((str ""))
+               (setq tmp2 (cdr rest))
+               (while (not (eq tmp tmp2))
+                 (setq tmp2 (cdr tmp2)
+                       str (concat str " dup")))
+               (byte-compile-log-lap "  %s%s %s\t-->\t%s%s dup"
+                                     lap0 str lap0 lap0 str)))
+         (setq keep-going t)
+         (setcar (car tmp) 'byte-dup)
+         (setcdr (car tmp) 0)
+         (setq rest tmp))
+        ;;
+        ;; TAG1: TAG2: --> TAG1: <deleted>
+        ;; (and other references to TAG2 are replaced with TAG1)
+        ;;
+        ((and (eq (car lap0) 'TAG)
+              (eq (car lap1) 'TAG))
+         (and (memq byte-optimize-log '(t byte))
+              (byte-compile-log "  adjacent tags %d and %d merged"
+                                (nth 1 lap1) (nth 1 lap0)))
+         (setq tmp3 lap)
+         (while (setq tmp2 (rassq lap0 tmp3))
+           (setcdr tmp2 lap1)
+           (setq tmp3 (cdr (memq tmp2 tmp3))))
+         (setq lap (delq lap0 lap)
+               keep-going t)
+          ;; replace references to tag in jump tables, if any
+          (dolist (table byte-compile-jump-tables)
+            (maphash #'(lambda (value tag)
+                         (when (equal tag lap0)
+                           (puthash value lap1 table)))
+                     table)))
+        ;;
+        ;; unused-TAG: --> <deleted>
+        ;;
+        ((and (eq 'TAG (car lap0))
+              (not (rassq lap0 lap))
+               ;; make sure this tag isn't used in a jump-table
+               (cl-loop for table in byte-compile-jump-tables
+                        when (member lap0 (hash-table-values table))
+                        return nil finally return t))
+         (and (memq byte-optimize-log '(t byte))
+              (byte-compile-log "  unused tag %d removed" (nth 1 lap0)))
+         (setq lap (delq lap0 lap)
+               keep-going t))
+        ;;
+        ;; goto   ... --> goto   <delete until TAG or end>
+        ;; return ... --> return <delete until TAG or end>
+        ;; (unless a jump-table is being used, where deleting may affect
+         ;; other valid case bodies)
+         ;;
+        ((and (memq (car lap0) '(byte-goto byte-return))
+              (not (memq (car lap1) '(TAG nil)))
+               ;; FIXME: Instead of deferring simply when jump-tables are
+               ;; being used, keep a list of tags used for switch tags and
+               ;; use them instead (see `byte-compile-inline-lapcode').
+               (not byte-compile-jump-tables))
+         (setq tmp rest)
+         (let ((i 0)
+               (opt-p (memq byte-optimize-log '(t lap)))
+               str deleted)
+           (while (and (setq tmp (cdr tmp))
+                       (not (eq 'TAG (car (car tmp)))))
+             (if opt-p (setq deleted (cons (car tmp) deleted)
+                             str (concat str " %s")
+                             i (1+ i))))
+           (if opt-p
+               (let ((tagstr
+                      (if (eq 'TAG (car (car tmp)))
+                          (format "%d:" (car (cdr (car tmp))))
+                        (or (car tmp) ""))))
+                 (if (< i 6)
+                     (apply 'byte-compile-log-lap-1
+                            (concat "  %s" str
+                                    " %s\t-->\t%s <deleted> %s")
+                            lap0
+                            (nconc (nreverse deleted)
+                                   (list tagstr lap0 tagstr)))
+                   (byte-compile-log-lap
+                    "  %s <%d unreachable op%s> %s\t-->\t%s <deleted> %s"
+                    lap0 i (if (= i 1) "" "s")
+                    tagstr lap0 tagstr))))
+           (rplacd rest tmp))
+         (setq keep-going t))
+        ;;
+        ;; <safe-op> unbind --> unbind <safe-op>
+        ;; (this may enable other optimizations.)
+        ;;
+        ((and (eq 'byte-unbind (car lap1))
+              (memq (car lap0) byte-after-unbind-ops))
+         (byte-compile-log-lap "  %s %s\t-->\t%s %s" lap0 lap1 lap1 lap0)
+         (setcar rest lap1)
+         (setcar (cdr rest) lap0)
+         (setq keep-going t))
+        ;;
+        ;; varbind-X unbind-N         -->  discard unbind-(N-1)
+        ;; save-excursion unbind-N    -->  unbind-(N-1)
+        ;; save-restriction unbind-N  -->  unbind-(N-1)
+        ;;
+        ((and (eq 'byte-unbind (car lap1))
+              (memq (car lap0) '(byte-varbind byte-save-excursion
+                                 byte-save-restriction))
+              (< 0 (cdr lap1)))
+         (if (zerop (setcdr lap1 (1- (cdr lap1))))
+             (delq lap1 rest))
+         (if (eq (car lap0) 'byte-varbind)
+             (setcar rest (cons 'byte-discard 0))
+           (setq lap (delq lap0 lap)))
+         (byte-compile-log-lap "  %s %s\t-->\t%s %s"
+                               lap0 (cons (car lap1) (1+ (cdr lap1)))
+                               (if (eq (car lap0) 'byte-varbind)
+                                   (car rest)
+                                 (car (cdr rest)))
+                               (if (and (/= 0 (cdr lap1))
+                                        (eq (car lap0) 'byte-varbind))
+                                   (car (cdr rest))
+                                 ""))
+         (setq keep-going t))
+        ;;
+        ;; goto*-X ... X: goto-Y  --> goto*-Y
+        ;; goto-X ...  X: return  --> return
+        ;;
+        ((and (memq (car lap0) byte-goto-ops)
+              (memq (car (setq tmp (nth 1 (memq (cdr lap0) lap))))
+                    '(byte-goto byte-return)))
+         (cond ((and (not (eq tmp lap0))
+                     (or (eq (car lap0) 'byte-goto)
+                         (eq (car tmp) 'byte-goto)))
+                (byte-compile-log-lap "  %s [%s]\t-->\t%s"
+                                      (car lap0) tmp tmp)
+                (if (eq (car tmp) 'byte-return)
+                    (setcar lap0 'byte-return))
+                (setcdr lap0 (cdr tmp))
+                (setq keep-going t))))
+        ;;
+        ;; goto-*-else-pop X ... X: goto-if-* --> whatever
+        ;; goto-*-else-pop X ... X: discard --> whatever
+        ;;
+        ((and (memq (car lap0) '(byte-goto-if-nil-else-pop
+                                 byte-goto-if-not-nil-else-pop))
+              (memq (car (car (setq tmp (cdr (memq (cdr lap0) lap)))))
+                    (eval-when-compile
+                      (cons 'byte-discard byte-conditional-ops)))
+              (not (eq lap0 (car tmp))))
+         (setq tmp2 (car tmp))
+         (setq tmp3 (assq (car lap0) '((byte-goto-if-nil-else-pop
+                                        byte-goto-if-nil)
+                                       (byte-goto-if-not-nil-else-pop
+                                        byte-goto-if-not-nil))))
+         (if (memq (car tmp2) tmp3)
+             (progn (setcar lap0 (car tmp2))
+                    (setcdr lap0 (cdr tmp2))
+                    (byte-compile-log-lap "  %s-else-pop [%s]\t-->\t%s"
+                                          (car lap0) tmp2 lap0))
+           ;; Get rid of the -else-pop's and jump one step further.
+           (or (eq 'TAG (car (nth 1 tmp)))
+               (setcdr tmp (cons (byte-compile-make-tag)
+                                 (cdr tmp))))
+           (byte-compile-log-lap "  %s [%s]\t-->\t%s <skip>"
+                                 (car lap0) tmp2 (nth 1 tmp3))
+           (setcar lap0 (nth 1 tmp3))
+           (setcdr lap0 (nth 1 tmp)))
+         (setq keep-going t))
+        ;;
+        ;; const goto-X ... X: goto-if-* --> whatever
+        ;; const goto-X ... X: discard   --> whatever
+        ;;
+        ((and (eq (car lap0) 'byte-constant)
+              (eq (car lap1) 'byte-goto)
+              (memq (car (car (setq tmp (cdr (memq (cdr lap1) lap)))))
+                    (eval-when-compile
+                      (cons 'byte-discard byte-conditional-ops)))
+              (not (eq lap1 (car tmp))))
+         (setq tmp2 (car tmp))
+         (cond ((when (consp (cdr lap0))
+                  (memq (car tmp2)
+                        (if (null (car (cdr lap0)))
+                            '(byte-goto-if-nil byte-goto-if-nil-else-pop)
+                          '(byte-goto-if-not-nil
+                            byte-goto-if-not-nil-else-pop))))
+                (byte-compile-log-lap "  %s goto [%s]\t-->\t%s %s"
+                                      lap0 tmp2 lap0 tmp2)
+                (setcar lap1 (car tmp2))
+                (setcdr lap1 (cdr tmp2))
+                ;; Let next step fix the (const,goto-if*) sequence.
+                (setq rest (cons nil rest))
+                (setq keep-going t))
+               ((or (consp (cdr lap0))
+                    (eq (car tmp2) 'byte-discard))
+                ;; Jump one step further
+                (byte-compile-log-lap
+                 "  %s goto [%s]\t-->\t<deleted> goto <skip>"
+                 lap0 tmp2)
                 (or (eq 'TAG (car (nth 1 tmp)))
                     (setcdr tmp (cons (byte-compile-make-tag)
                                       (cdr tmp))))
-                (byte-compile-log-lap "  %s [%s]\t-->\t%s <skip>"
-                                      (car lap0) tmp2 (nth 1 tmp3))
-                (setcar lap0 (nth 1 tmp3))
-                (setcdr lap0 (nth 1 tmp)))
-              (setq keep-going t))
-             ;;
-             ;; const goto-X ... X: goto-if-* --> whatever
-             ;; const goto-X ... X: discard   --> whatever
-             ;;
-             ((and (eq (car lap0) 'byte-constant)
-                   (eq (car lap1) 'byte-goto)
-                   (memq (car (car (setq tmp (cdr (memq (cdr lap1) lap)))))
-                         (eval-when-compile
-                           (cons 'byte-discard byte-conditional-ops)))
-                   (not (eq lap1 (car tmp))))
-              (setq tmp2 (car tmp))
-              (cond ((when (consp (cdr lap0))
-                       (memq (car tmp2)
-                             (if (null (car (cdr lap0)))
-                                 '(byte-goto-if-nil byte-goto-if-nil-else-pop)
-                               '(byte-goto-if-not-nil
-                                 byte-goto-if-not-nil-else-pop))))
-                     (byte-compile-log-lap "  %s goto [%s]\t-->\t%s %s"
-                                           lap0 tmp2 lap0 tmp2)
-                     (setcar lap1 (car tmp2))
-                     (setcdr lap1 (cdr tmp2))
-                     ;; Let next step fix the (const,goto-if*) sequence.
-                     (setq rest (cons nil rest))
-                     (setq keep-going t))
-                    ((or (consp (cdr lap0))
-                         (eq (car tmp2) 'byte-discard))
-                     ;; Jump one step further
-                     (byte-compile-log-lap
-                      "  %s goto [%s]\t-->\t<deleted> goto <skip>"
-                      lap0 tmp2)
-                     (or (eq 'TAG (car (nth 1 tmp)))
-                         (setcdr tmp (cons (byte-compile-make-tag)
-                                           (cdr tmp))))
-                     (setcdr lap1 (car (cdr tmp)))
-                     (setq lap (delq lap0 lap))
-                     (setq keep-going t))))
-             ;;
-             ;; X: varref-Y    ...     varset-Y goto-X  -->
-             ;; X: varref-Y Z: ... dup varset-Y goto-Z
-             ;; (varset-X goto-BACK, BACK: varref-X --> copy the varref down.)
-             ;; (This is so usual for while loops that it is worth handling).
-              ;;
-              ;; Here again, we could do it for stack-ref/stack-set, but
-             ;; that's replacing a stack-ref-Y with a stack-ref-0, which
-              ;; is a very minor improvement (if any), at the cost of
-             ;; more stack use and more byte-code.  Let's not do it.
-             ;;
-             ((and (eq (car lap1) 'byte-varset)
-                   (eq (car lap2) 'byte-goto)
-                   (not (memq (cdr lap2) rest)) ;Backwards jump
-                   (eq (car (car (setq tmp (cdr (memq (cdr lap2) lap)))))
-                       'byte-varref)
-                   (eq (cdr (car tmp)) (cdr lap1))
-                   (not (memq (car (cdr lap1)) byte-boolean-vars)))
-              ;;(byte-compile-log-lap "  Pulled %s to end of loop" (car tmp))
-              (let ((newtag (byte-compile-make-tag)))
-                (byte-compile-log-lap
-                 "  %s: %s ... %s %s\t-->\t%s: %s %s: ... %s %s %s"
-                 (nth 1 (cdr lap2)) (car tmp)
-                  lap1 lap2
-                 (nth 1 (cdr lap2)) (car tmp)
-                 (nth 1 newtag) 'byte-dup lap1
-                 (cons 'byte-goto newtag)
-                 )
-                (setcdr rest (cons (cons 'byte-dup 0) (cdr rest)))
-                (setcdr tmp (cons (setcdr lap2 newtag) (cdr tmp))))
-              (setq add-depth 1)
-              (setq keep-going t))
-             ;;
-             ;; goto-X Y: ... X: goto-if*-Y  -->  goto-if-not-*-X+1 Y:
-             ;; (This can pull the loop test to the end of the loop)
-             ;;
-             ((and (eq (car lap0) 'byte-goto)
-                   (eq (car lap1) 'TAG)
-                   (eq lap1
-                       (cdr (car (setq tmp (cdr (memq (cdr lap0) lap))))))
-                   (memq (car (car tmp))
-                         '(byte-goto byte-goto-if-nil byte-goto-if-not-nil
-                                     byte-goto-if-nil-else-pop)))
-;;            (byte-compile-log-lap "  %s %s, %s %s  --> moved conditional"
-;;                                  lap0 lap1 (cdr lap0) (car tmp))
-              (let ((newtag (byte-compile-make-tag)))
-                (byte-compile-log-lap
-                 "%s %s: ... %s: %s\t-->\t%s ... %s:"
-                 lap0 (nth 1 lap1) (nth 1 (cdr lap0)) (car tmp)
-                 (cons (cdr (assq (car (car tmp))
-                                  '((byte-goto-if-nil . byte-goto-if-not-nil)
-                                    (byte-goto-if-not-nil . byte-goto-if-nil)
-                                    (byte-goto-if-nil-else-pop .
-                                     byte-goto-if-not-nil-else-pop)
-                                    (byte-goto-if-not-nil-else-pop .
-                                     byte-goto-if-nil-else-pop))))
-                       newtag)
-
-                 (nth 1 newtag)
-                 )
-                (setcdr tmp (cons (setcdr lap0 newtag) (cdr tmp)))
-                (if (eq (car (car tmp)) 'byte-goto-if-nil-else-pop)
-                    ;; We can handle this case but not the -if-not-nil case,
-                    ;; because we won't know which non-nil constant to push.
-                  (setcdr rest (cons (cons 'byte-constant
-                                           (byte-compile-get-constant nil))
-                                     (cdr rest))))
-              (setcar lap0 (nth 1 (memq (car (car tmp))
-                                        '(byte-goto-if-nil-else-pop
-                                          byte-goto-if-not-nil
-                                          byte-goto-if-nil
-                                          byte-goto-if-not-nil
-                                          byte-goto byte-goto))))
-              )
-              (setq keep-going t))
-             )
+                (setcdr lap1 (car (cdr tmp)))
+                (setq lap (delq lap0 lap))
+                (setq keep-going t))))
+        ;;
+        ;; X: varref-Y    ...     varset-Y goto-X  -->
+        ;; X: varref-Y Z: ... dup varset-Y goto-Z
+        ;; (varset-X goto-BACK, BACK: varref-X --> copy the varref down.)
+        ;; (This is so usual for while loops that it is worth handling).
+         ;;
+         ;; Here again, we could do it for stack-ref/stack-set, but
+        ;; that's replacing a stack-ref-Y with a stack-ref-0, which
+         ;; is a very minor improvement (if any), at the cost of
+        ;; more stack use and more byte-code.  Let's not do it.
+        ;;
+        ((and (eq (car lap1) 'byte-varset)
+              (eq (car lap2) 'byte-goto)
+              (not (memq (cdr lap2) rest)) ;Backwards jump
+              (eq (car (car (setq tmp (cdr (memq (cdr lap2) lap)))))
+                  'byte-varref)
+              (eq (cdr (car tmp)) (cdr lap1))
+              (not (memq (car (cdr lap1)) byte-boolean-vars)))
+         ;;(byte-compile-log-lap "  Pulled %s to end of loop" (car tmp))
+         (let ((newtag (byte-compile-make-tag)))
+           (byte-compile-log-lap
+            "  %s: %s ... %s %s\t-->\t%s: %s %s: ... %s %s %s"
+            (nth 1 (cdr lap2)) (car tmp)
+             lap1 lap2
+            (nth 1 (cdr lap2)) (car tmp)
+            (nth 1 newtag) 'byte-dup lap1
+            (cons 'byte-goto newtag)
+            )
+           (setcdr rest (cons (cons 'byte-dup 0) (cdr rest)))
+           (setcdr tmp (cons (setcdr lap2 newtag) (cdr tmp))))
+         (setq add-depth 1)
+         (setq keep-going t))
+        ;;
+        ;; goto-X Y: ... X: goto-if*-Y  -->  goto-if-not-*-X+1 Y:
+        ;; (This can pull the loop test to the end of the loop)
+        ;;
+        ((and (eq (car lap0) 'byte-goto)
+              (eq (car lap1) 'TAG)
+              (eq lap1
+                  (cdr (car (setq tmp (cdr (memq (cdr lap0) lap))))))
+              (memq (car (car tmp))
+                    '(byte-goto byte-goto-if-nil byte-goto-if-not-nil
+                      byte-goto-if-nil-else-pop)))
+         ;;           (byte-compile-log-lap "  %s %s, %s %s  --> moved 
conditional"
+         ;;                                 lap0 lap1 (cdr lap0) (car tmp))
+         (let ((newtag (byte-compile-make-tag)))
+           (byte-compile-log-lap
+            "%s %s: ... %s: %s\t-->\t%s ... %s:"
+            lap0 (nth 1 lap1) (nth 1 (cdr lap0)) (car tmp)
+            (cons (cdr (assq (car (car tmp))
+                             '((byte-goto-if-nil . byte-goto-if-not-nil)
+                               (byte-goto-if-not-nil . byte-goto-if-nil)
+                               (byte-goto-if-nil-else-pop .
+                                                          
byte-goto-if-not-nil-else-pop)
+                               (byte-goto-if-not-nil-else-pop .
+                                                              
byte-goto-if-nil-else-pop))))
+                  newtag)
+
+            (nth 1 newtag)
+            )
+           (setcdr tmp (cons (setcdr lap0 newtag) (cdr tmp)))
+           (if (eq (car (car tmp)) 'byte-goto-if-nil-else-pop)
+               ;; We can handle this case but not the -if-not-nil case,
+               ;; because we won't know which non-nil constant to push.
+               (setcdr rest (cons (cons 'byte-constant
+                                        (byte-compile-get-constant nil))
+                                  (cdr rest))))
+           (setcar lap0 (nth 1 (memq (car (car tmp))
+                                     '(byte-goto-if-nil-else-pop
+                                       byte-goto-if-not-nil
+                                       byte-goto-if-nil
+                                       byte-goto-if-not-nil
+                                       byte-goto byte-goto))))
+           )
+         (setq keep-going t))
+        )
        (setq rest (cdr rest)))
       )
     ;; Cleanup stage:



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