master 9022df7: Optimise c-parse-state for large buffers with few (if any) braces.

[Alan Mackenzie]

branch: master
commit 9022df70270243f211c54ccd66800320148b8434
Author: Alan Mackenzie <acm@muc.de>
Commit: Alan Mackenzie <acm@muc.de>

    Optimise c-parse-state for large buffers with few (if any) braces.
    
    * lisp/progmodes/cc-engine (c-get-fallback-scan-pos): Search a maximum of
    50,000 characters back for the two BODs.  Return nil if we dont' find them.
    (c-parse-state-get-strategy): For strategy `forward', always use the 
position
    `good-pos' for `start-point', even when there's a change of current macro.
    Deal with a possible return value of nil from c-get-fallback-scan-pos (as
    above).
    (c-invalidate-state-cache-1): For `c-state-cache-good-pos', instead of
    sometimes using the minimum scan pos (leading to extensive scanning of the
    entire buffer) use a point close to `here'.
---
 lisp/progmodes/cc-engine.el | 37 ++++++++++++++++++++++---------------
 1 file changed, 22 insertions(+), 15 deletions(-)

diff --git a/lisp/progmodes/cc-engine.el b/lisp/progmodes/cc-engine.el
index f14ffb3..68dadcc 100644
--- a/lisp/progmodes/cc-engine.el
+++ b/lisp/progmodes/cc-engine.el
@@ -3568,15 +3568,19 @@ mhtml-mode."
   ;; Return a start position for building `c-state-cache' from
   ;; scratch.  This will be at the top level, 2 defuns back.
   (save-excursion
-    ;; Go back 2 bods, but ignore any bogus positions returned by
-    ;; beginning-of-defun (i.e. open paren in column zero).
-    (goto-char here)
-    (let ((cnt 2))
-      (while (not (or (bobp) (zerop cnt)))
-       (c-beginning-of-defun-1)        ; Pure elisp BOD.
-       (if (eq (char-after) ?\{)
-           (setq cnt (1- cnt)))))
-    (point)))
+    (save-restriction
+      (when (> here (* 10 c-state-cache-too-far))
+       (narrow-to-region (- here (* 10 c-state-cache-too-far)) here))
+      ;; Go back 2 bods, but ignore any bogus positions returned by
+      ;; beginning-of-defun (i.e. open paren in column zero).
+      (goto-char here)
+      (let ((cnt 2))
+       (while (not (or (bobp) (zerop cnt)))
+         (c-beginning-of-defun-1)      ; Pure elisp BOD.
+         (if (eq (char-after) ?\{)
+             (setq cnt (1- cnt)))))
+      (and (not (bobp))
+          (point)))))
 
 (defun c-state-balance-parens-backwards (here- here+ top)
   ;; Return the position of the opening paren/brace/bracket before HERE- which
@@ -3667,9 +3671,7 @@ mhtml-mode."
            how-far 0))
      ((<= good-pos here)
       (setq strategy 'forward
-           start-point (if changed-macro-start
-                           cache-pos
-                         (max good-pos cache-pos))
+           start-point (max good-pos cache-pos)
            how-far (- here start-point)))
      ((< (- good-pos here) (- here cache-pos)) ; FIXME!!! ; apply some sort of 
weighting.
       (setq strategy 'backward
@@ -3688,7 +3690,8 @@ mhtml-mode."
               ;; (not (c-major-mode-is 'c++-mode))
               (> how-far c-state-cache-too-far))
       (setq BOD-pos (c-get-fallback-scan-pos here)) ; somewhat EXPENSIVE!!!
-      (if (< (- here BOD-pos) how-far)
+      (if (and BOD-pos
+              (< (- here BOD-pos) how-far))
          (setq strategy 'BOD
                start-point BOD-pos)))
 
@@ -4337,8 +4340,12 @@ mhtml-mode."
       (if (and dropped-cons
               (<= too-high-pa here))
          (c-append-lower-brace-pair-to-state-cache too-high-pa here here-bol))
-      (setq c-state-cache-good-pos (or (c-state-cache-after-top-paren)
-                                      (c-state-get-min-scan-pos)))))
+      (if (and c-state-cache-good-pos (< here c-state-cache-good-pos))
+         (setq c-state-cache-good-pos
+               (or (save-excursion
+                     (goto-char here)
+                     (c-literal-start))
+                   here)))))
 
   ;; The brace-pair desert marker:
   (when (car c-state-brace-pair-desert)