[PATCH] Optimize certain memq forms during byte-compilation.

[PATCH] Optimize certain memq forms during byte-compilation.

[Vibhav Pant]

* lisp/emacs-lisp/byte-opt.el (byte-optimize-memq): New function.
  Set the byte optimizer function for memq to byte-optimize-memq.
---
 lisp/emacs-lisp/byte-opt.el | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/lisp/emacs-lisp/byte-opt.el b/lisp/emacs-lisp/byte-opt.el
index a316364761..e4c5300b0e 100644
--- a/lisp/emacs-lisp/byte-opt.el
+++ b/lisp/emacs-lisp/byte-opt.el
@@ -892,7 +892,20 @@ byte-optimize-identity
 		       (if (= 1 (length (cdr form))) "" "s"))
     form))
 
+(defun byte-optimize-memq (form)
+  (if (/= (length (cdr form)) 2)
+      (byte-compile-warn "memq called with %d arg%s, but requires 2"
+		         (length (cdr form))
+		         (if (= 1 (length (cdr form))) "" "s"))
+    (let ((list (nth 2 form)))
+      (when (and (eq (car-safe list) 'quote)
+             (listp (setq list (cadr list)))
+             (= (length list) 1))
+        (setq form (list 'eq (nth 1 form) (list 'quote (nth 0 list))))))
+    (byte-optimize-predicate form)))
+
 (put 'identity 'byte-optimizer 'byte-optimize-identity)
+(put 'memq 'byte-optimizer 'byte-optimize-memq)
 
 (put '+   'byte-optimizer 'byte-optimize-plus)
 (put '*   'byte-optimizer 'byte-optimize-multiply)
@@ -915,7 +928,6 @@ byte-optimize-identity
 (put '1-  'byte-optimizer 'byte-optimize-predicate)
 (put 'not 'byte-optimizer 'byte-optimize-predicate)
 (put 'null  'byte-optimizer 'byte-optimize-predicate)
-(put 'memq  'byte-optimizer 'byte-optimize-predicate)
 (put 'consp 'byte-optimizer 'byte-optimize-predicate)
 (put 'listp 'byte-optimizer 'byte-optimize-predicate)
 (put 'symbolp 'byte-optimizer 'byte-optimize-predicate)
@@ -933,7 +945,6 @@ byte-optimize-identity
 (put 'car-safe 'byte-optimizer 'byte-optimize-predicate)
 (put 'cdr-safe 'byte-optimizer 'byte-optimize-predicate)
 
-
 ;; I'm not convinced that this is necessary.  Doesn't the optimizer loop
 ;; take care of this? - Jamie
 ;; I think this may some times be necessary to reduce ie (quote 5) to 5,
-- 
2.16.2

Re: [PATCH] Optimize certain memq forms during byte-compilation.

[Robert Pluim]

Vibhav Pant <vibhavp@gmail.com> writes:

> * lisp/emacs-lisp/byte-opt.el (byte-optimize-memq): New function.
>   Set the byte optimizer function for memq to byte-optimize-memq.

Is (memq foo '(bar)) actually that common? In any case, some
explanation of the intent of the change would be helpful so we don't
need to read the code every time.

Robert

Re: [PATCH] Optimize certain memq forms during byte-compilation.

[Vibhav Pant]

On Fri, Mar 23, 2018 at 2:26 PM, Robert Pluim <rpluim@gmail.com> wrote:
> Is (memq foo '(bar)) actually that common?

I've seen it used in the emacs lisp code base, mostly for detecting
the system-type.

> In any case, some explanation of the intent of the change would be helpful
> so we don't need to read the code every time.

I'll add a comment explaining the optimization, yeah.

Thanks,
Vibhav

-- 
Vibhav Pant
vibhavp@gmail.com