org-element--parse-to: Micro optimizations

* lisp/org-element.el (org-element-headline-parser): Store :true-level
property.
(org-element--parse-to): Call `org-get-limited-outline-regexp'
directly rather than via `org-with-limited-levels'.  Avoid moving
point unnecessarily.  Prefer `org-headline-re' to generate regexps.
* lisp/org-macs.el (org-headline-re):
(org-skip-whitespace): Inline.

lisp/org-element.el

@@ -1188,6 +1188,7 @@ Assume point is at beginning of the headline."
 			  :contents-end contents-end
                           :robust-begin robust-begin
                           :robust-end robust-end
+                          :true-level true-level
 			  :level level
 			  :priority priority
 			  :tags tags
@@ -6472,7 +6473,10 @@ the expected result."
             ;; buffer above.  This comes at the cost of not calculating
             ;; `:parent' property for headings.
             ((not cached)
-             (if (org-with-limited-levels (outline-previous-heading))
+             (end-of-line) ; ensure the end of current heading.
+             (if (re-search-backward
+                  (org-get-limited-outline-regexp t)
+                  nil 'move)
                  (progn
                    (setq element (org-element-headline-parser nil 'fast))
 	           (setq mode 'planning)
@@ -6502,11 +6506,11 @@ the expected result."
              (let ((up cached)
                    (pos (if (= (point-max) pos) (1- pos) pos)))
                (while (and up (<= (org-element-property :end up) pos))
-                 (goto-char (org-element-property :end up))
-                 (setq element up
+                 (setq next (org-element-property :end up)
+                       element up
                        mode (org-element--next-mode (org-element-property :mode element) (org-element-type element) nil)
-                       up (org-element-property :parent up)
-                       next (point)))
+                       up (org-element-property :parent up)))
+               (when next (goto-char next))
                (when up (setq element up)))))
            ;; Parse successively each element until we reach POS.
            (let ((end (or (org-element-property :end element) (point-max)))
@@ -6543,7 +6547,7 @@ If you observe Emacs hangs frequently, please report this to Org mode mailing li
                      (setq element (or (org-element--cache-put element) element))
                    ;; Nothing to parse (i.e. empty file).
                    (throw 'exit parent))
-                 (unless (or (not (org-element--cache-active-p)) parent)
+                 (unless (or parent (not (org-element--cache-active-p)))
                    (org-element--cache-warn
                     "Got empty parent while parsing. Please report it to Org mode mailing list (M-x org-submit-bug-report).\n Backtrace:\n%S"
                     (when (and (fboundp 'backtrace-get-frames)
@@ -6564,13 +6568,9 @@ If you observe Emacs hangs frequently, please report this to Org mode mailing li
                    (goto-char elem-end)
                    (when (eq type 'headline)
                      (save-match-data
-                       (unless (when (and (/= 1 (org-element-property :level element))
+                       (unless (when (and (/= 1 (org-element-property :true-level element))
                                           (re-search-forward
-                                           (rx-to-string
-                                            `(and bol (repeat 1 ,(1- (let ((level (org-element-property :level element)))
-                                                                       (if org-odd-levels-only (1- (* level 2)) level)))
-                                                              "*")
-                                                  " "))
+                                           (org-headline-re (1- (org-element-property :true-level element)))
                                            pos t))
                                  (beginning-of-line)
                                  t)
@@ -6582,11 +6582,7 @@ If you observe Emacs hangs frequently, please report this to Org mode mailing li
                          (goto-char pos)
                          (unless
                              (re-search-backward
-                              (rx-to-string
-                               `(and bol (repeat ,(let ((level (org-element-property :level element)))
-                                                    (if org-odd-levels-only (1- (* level 2)) level))
-                                                 "*")
-                                     " "))
+                              (org-headline-re (org-element-property :true-level element))
                               elem-end t)
                            ;; Roll-back to normal parsing.
                            (goto-char elem-end)))))

lisp/org-macs.el

@@ -811,7 +811,7 @@ get an unnecessary O(N²) space complexity, so you're usually better off using
   "Plist holding association between headline level regexp.")
 (defvar org--headline-re-cache-bol nil
   "Plist holding association between headline level regexp.")
-(defun org-headline-re (true-level &optional no-bol)
+(defsubst org-headline-re (true-level &optional no-bol)
   "Generate headline regexp for TRUE-LEVEL.
 When NO-BOL is non-nil, regexp will not demand the regexp to start at
 beginning of line."
@@ -964,7 +964,7 @@ Return nil when PROP is not set at POS."
        (<= (match-beginning n) pos)
        (>= (match-end n) pos)))
 
-(defun org-skip-whitespace ()
+(defsubst org-skip-whitespace ()
   "Skip over space, tabs and newline characters."
   (skip-chars-forward " \t\n\r"))