Improve cache update for deleted lines

If multiple adjacent lines have been deleted, drop wads and adjust wads in one
go instead of doing it for each delete line individually.

For certain buffer contents such as a block comment that spans thousands of
lines, this change reduces the cache update time from many seconds to a few
dozen (or at worst at few hundred) milliseconds.

code/cache.lisp

@@ -285,10 +285,11 @@
         do (process-next-wad cache line-number))
   (adjust-worklist-and-suffix cache 1))
 
-(defun handle-deleted-line (cache line-number)
-  (loop until (next-wad-is-beyond-line-p cache line-number)
-        do (process-next-wad cache line-number))
-  (adjust-worklist-and-suffix cache -1))
+(defun handle-deleted-lines (cache line-number line-count)
+  (loop :for line :from (- line-number line-count 1) :to line-number
+        :do (loop :until (next-wad-is-beyond-line-p cache line)
+                  :do (process-next-wad cache line)))
+  (adjust-worklist-and-suffix cache (- line-count)))
 
 ;;; Take into account modifications to the buffer by destroying the
 ;;; parts of the cache that are no longer valid, while keeping parse
@@ -304,20 +305,25 @@
                  (setf cache-initialized-p t)
                  (ensure-update-initialized cache line-counter)))
              ;; Line deletion
-             (delete-cache-line ()
-               (flx:delete* lines line-counter)
-               (flx:delete* cluffer-lines line-counter)
-               (handle-deleted-line cache line-counter))
+             (delete-cache-lines (start-line-number end-line-number)
+               (let ((count (- end-line-number start-line-number)))
+                 (loop :repeat count
+                       :do (flx:delete* lines start-line-number)
+                           (flx:delete* cluffer-lines start-line-number))
+                 (handle-deleted-lines cache (1- end-line-number) count)))
              (remove-deleted-lines (line)
                ;; Look at cache lines starting at LINE-COUNTER. Delete
                ;; all cache lines that do not have LINE as their
                ;; associated cluffer line. Those lines correspond to
                ;; deleted lines between the previously processed line
                ;; and LINE.
-               (loop for cluffer-line
-                        = (flx:element* cluffer-lines line-counter)
-                     until (eq line cluffer-line)
-                     do (delete-cache-line)))
+               (loop :for end-line-number :from line-counter
+                     :for cluffer-line
+                        = (flx:element* cluffer-lines end-line-number)
+                     :until (eq line cluffer-line)
+                     :finally (when (< line-counter end-line-number)
+                                (delete-cache-lines
+                                 line-counter end-line-number))))
              ;; Handlers for Cluffer's update protocol events.
              (skip (count)
                (incf line-counter count))
@@ -344,10 +350,11 @@
                             (time-stamp cache)
                             #'sync #'skip #'modify #'create))
       ;; Remove trailing cache lines after the last
-      ;; skipped/modified/... cache line, that no longer correspond
-      ;; to existing lines in the cluffer buffer.
-      (loop while (< line-counter (flx:nb-elements lines))
-            do (delete-cache-line))))
+      ;; skipped/modified/... cache line, that no longer correspond to
+      ;; existing lines in the cluffer buffer.
+      (let ((cache-line-count (flx:nb-elements lines)))
+        (when (< line-counter cache-line-count)
+          (delete-cache-lines line-counter cache-line-count)))))
   (finish-scavenge cache))
 
 (defmethod line-count ((cache cache))