bug#48261: 28.0.50; Optimize `eql' to `eq' for fixnums

bug#48261: 28.0.50; Optimize `eql' to `eq' for fixnums

[Philipp Stephani]

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It would be nice if the byte optimizer could optimize `eql' to `eq' if
one of the arguments is guaranteed to be a fixnum.  Patch is attached.

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From 8b6f76df20454bb0caaba71cac9c5c3a7cb2aa62 Mon Sep 17 00:00:00 2001
From: Philipp Stephani <phst@google.com>
Date: Thu, 6 May 2021 19:13:00 +0200
Subject: [PATCH] Optimize calls to 'eql', 'memql' and similar for fixnums.

It's good practice to compare integers using 'eql' because two bignum
objects representing the same integer might not be 'eq'.  However,
'eql' is slower and doesn't have its own byte code.  Therefore,
replace it with 'eq' if one argument is guaranteed to be a fixnum on
all platforms.

* lisp/emacs-lisp/byte-opt.el (byte-optimize--fixnump): New helper
function.
(byte-optimize-equal, byte-optimize-member, byte-optimize-assoc): Use
it to optimize 'eql' etc. to 'eq' if it will always compare fixnums.
---
 lisp/emacs-lisp/byte-opt.el | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/lisp/emacs-lisp/byte-opt.el b/lisp/emacs-lisp/byte-opt.el
index 33b4d4b3c8..4dd8b90b3a 100644
--- a/lisp/emacs-lisp/byte-opt.el
+++ b/lisp/emacs-lisp/byte-opt.el
@@ -951,12 +951,20 @@ byte-optimize--constant-symbol-p
   "Whether EXPR is a constant symbol."
   (and (macroexp-const-p expr) (symbolp (eval expr))))
 
+(defun byte-optimize--fixnump (o)
+  "Return whether O is guaranteed to be a fixnum in all Emacsen.
+See Info node `(elisp) Integer Basics'."
+  (and (fixnump o) (<= -536870912 o 536870911)))
+
 (defun byte-optimize-equal (form)
-  ;; Replace `equal' or `eql' with `eq' if at least one arg is a symbol.
+  ;; Replace `equal' or `eql' with `eq' if at least one arg is a
+  ;; symbol or fixnum.
   (byte-optimize-binary-predicate
    (if (= (length (cdr form)) 2)
        (if (or (byte-optimize--constant-symbol-p (nth 1 form))
-               (byte-optimize--constant-symbol-p (nth 2 form)))
+               (byte-optimize--constant-symbol-p (nth 2 form))
+               (byte-optimize--fixnump (nth 1 form))
+               (byte-optimize--fixnump (nth 2 form)))
            (cons 'eq (cdr form))
          form)
      ;; Arity errors reported elsewhere.
@@ -964,14 +972,18 @@ byte-optimize-equal
 
 (defun byte-optimize-member (form)
   ;; Replace `member' or `memql' with `memq' if the first arg is a symbol,
-  ;; or the second arg is a list of symbols.
+  ;; or the second arg is a list of symbols.  Same with fixnums.
   (if (= (length (cdr form)) 2)
       (if (or (byte-optimize--constant-symbol-p (nth 1 form))
+              (byte-optimize--fixnump (nth 1 form))
               (let ((arg2 (nth 2 form)))
                 (and (macroexp-const-p arg2)
                      (let ((listval (eval arg2)))
                        (and (listp listval)
-                            (not (memq nil (mapcar #'symbolp listval))))))))
+                            (cl-every
+                             (lambda (o)
+                               (or (symbolp o) (byte-optimize--fixnump o)))
+                             listval))))))
           (cons 'memq (cdr form))
         form)
     ;; Arity errors reported elsewhere.
@@ -979,11 +991,12 @@ byte-optimize-member
 
 (defun byte-optimize-assoc (form)
   ;; Replace 2-argument `assoc' with `assq', `rassoc' with `rassq',
-  ;; if the first arg is a symbol.
+  ;; if the first arg is a symbol or fixnum.
   (cond
    ((/= (length form) 3)
     form)
-   ((byte-optimize--constant-symbol-p (nth 1 form))
+   ((or (byte-optimize--constant-symbol-p (nth 1 form))
+        (byte-optimize--fixnump (nth 1 form)))
     (cons (if (eq (car form) 'assoc) 'assq 'rassq)
           (cdr form)))
    (t (byte-optimize-constant-args form))))
-- 
2.31.1.607.g51e8a6a459-goog


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In GNU Emacs 28.0.50 (build 95, x86_64-pc-linux-gnu, GTK+ Version 3.24.24, cairo version 1.16.0)
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bug#48261: 28.0.50; Optimize `eql' to `eq' for fixnums

[Mattias Engdegård]

Good!

+  (and (fixnump o) (<= -536870912 o 536870911)))

Maybe write (<= (- (ash 1 29)) o (1- (ash 1 29))) instead.

+                            (cl-every

Are you sure this is a good idea? See comment in the beginning of bytecomp.el.
Maybe just hold your nose and keep the existing (memq nil (mapcar ...)) hack; the list is usually short.

(We really should have fast, readable, always-available standard functions or macros for 'some' and 'every' on lists.)

bug#48261: [External] : bug#48261: 28.0.50; Optimize `eql' to `eq' for fixnums

[Drew Adams]

> (We really should have fast, readable, always-available 
> standard functions or macros for 'some' and 'every' on lists.)

Does this qualify?

(defun some-elt-p (xs pred)
  "Return non-nil if (PRED X) is true for some element of list XS."
  (catch 'some-element-p
    (dolist (x  xs)
      (and (funcall pred x)  (throw 'some-element-p t)))))

(defun all-elts-p (xs pred)
  "Return non-nil if (PRED X) is true for all elements of list XS."
  (catch 'all-elts-p
    (dolist (x  xs  t)
      (or (funcall pred x)  (throw 'all-elts-p nil)))))

[I think I'd prefer the opposite arg order: PRED first,
 but this is at least the same as what CL uses.  Consider
 (apply-partially #'some-elt-p PRED), for instance.]

bug#48261: 28.0.50; Optimize `eql' to `eq' for fixnums

[Philipp]

> Am 07.05.2021 um 11:23 schrieb Mattias Engdegård <mattiase@acm.org>:
> +                            (cl-every
> 
> Are you sure this is a good idea? See comment in the beginning of bytecomp.el.

Yeah, good catch, will revert to the non-CL code before pushing.

bug#48261: 28.0.50; Optimize `eql' to `eq' for fixnums

[Mattias Engdegård]

8 maj 2021 kl. 11.17 skrev Philipp <p.stephani2@gmail.com>:

> Yeah, good catch, will revert to the non-CL code before pushing.

Fire at will!

bug#48261: 28.0.50; Optimize `eql' to `eq' for fixnums

[Philipp Stephani]

Am Sa., 8. Mai 2021 um 15:26 Uhr schrieb Mattias Engdegård <mattiase@acm.org>:
>
> 8 maj 2021 kl. 11.17 skrev Philipp <p.stephani2@gmail.com>:
>
> > Yeah, good catch, will revert to the non-CL code before pushing.
>
> Fire at will!
>

Pushed as 01bd4d1a824816fba34571623a65c9c1541c27e5.