Speed up lookup in redisplay--variables

* lisp/frame.el (redisplay--variables): Make it a hash-table.

* src/xdisp.c (maybe_set_redisplay): Access redisplay--variables
as a hash-table.  This speeds up this function by an order of
magnitude: where previously a setq was slowed down by 100% by
introducing the maybe_set_redisplay test, it is now only 5%
slower.
(syms_of_xdisp) <redisplay--variables>: Doc fix.

1 files changed, 4 insertions, 2 deletions

diff --git a/lisp/frame.el b/lisp/frame.el
index 4b23cb20ac4..3f31a2973c6 100644
--- a/lisp/frame.el
+++ b/lisp/frame.el
@@ -2231,8 +2231,10 @@ See also `toggle-frame-maximized'."
 (make-obsolete-variable
  'window-system-version "it does not give useful information." "24.3")
 
-;; These variables should trigger redisplay of the current buffer.
-(setq redisplay--variables
+;; Variables which should trigger redisplay of the current buffer.
+(setq redisplay--variables (make-hash-table :test 'eq :size 10))
+(mapc (lambda (var)
+        (puthash var 1 redisplay--variables))
       '(line-spacing
         overline-margin
         line-prefix