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master e55855c5a1e 1/2: Better compilation of n-ary comparisons
From: |
Mattias Engdegård |
Subject: |
master e55855c5a1e 1/2: Better compilation of n-ary comparisons |
Date: |
Sun, 29 Jan 2023 08:32:00 -0500 (EST) |
branch: master
commit e55855c5a1e85e230d2860c973358a34eb72da64
Author: Mattias Engdegård <mattiase@acm.org>
Commit: Mattias Engdegård <mattiase@acm.org>
Better compilation of n-ary comparisons
Transform n-ary comparisons to a chain of binary comparisons in the
Lisp optimiser instead of in codegen, to allow for subsequent
optimisations. This generalises the transform, so that
(< 1 X 10) -> (let ((x X)) (and (< 1 x) (< x 10)))
where (< 1 x) is then flipped to (> x 1) in codegen since it's
slightly more efficient to have the constant argument last. Arguments
that are neither constants nor variables are given temporary bindings.
This results in about 2× speedup for 3-ary comparisons of fixnums with
nontrivial arguments, and also improves the code slightly for binary
comparisons with a constant first argument.
* lisp/emacs-lisp/byte-opt.el (byte-opt--nary-comparison): New,
set as the `byte-optimizer` property for =, <, <=, >, and >=.
* lisp/emacs-lisp/bytecomp.el (byte-compile-and-folded):
Rename to...
(byte-compile-cmp): ...and rewrite.
---
lisp/emacs-lisp/byte-opt.el | 44 +++++++++++++++++++++++++++++++++++++++++++-
lisp/emacs-lisp/bytecomp.el | 38 ++++++++++++++++++++------------------
2 files changed, 63 insertions(+), 19 deletions(-)
diff --git a/lisp/emacs-lisp/byte-opt.el b/lisp/emacs-lisp/byte-opt.el
index b1a46d520e6..4d39e28fc8e 100644
--- a/lisp/emacs-lisp/byte-opt.el
+++ b/lisp/emacs-lisp/byte-opt.el
@@ -975,6 +975,43 @@ for speeding up processing.")
(t ;; Moving the constant to the end can enable some lapcode optimizations.
(list (car form) (nth 2 form) (nth 1 form)))))
+(defun byte-opt--nary-comparison (form)
+ "Optimise n-ary comparisons such as `=', `<' etc."
+ (let ((nargs (length (cdr form))))
+ (cond
+ ((= nargs 1)
+ `(progn (cadr form) t))
+ ((>= nargs 3)
+ ;; At least 3 arguments: transform to N-1 binary comparisons,
+ ;; since those have their own byte-ops which are particularly
+ ;; fast for fixnums.
+ (let* ((op (car form))
+ (bindings nil)
+ (rev-args nil))
+ (if (memq nil (mapcar #'macroexp-copyable-p (cddr form)))
+ ;; At least one arg beyond the first is non-constant non-variable:
+ ;; create temporaries for all args to guard against side-effects.
+ ;; The optimiser will eliminate trivial bindings later.
+ (let ((i 1))
+ (dolist (arg (cdr form))
+ (let ((var (make-symbol (format "arg%d" i))))
+ (push var rev-args)
+ (push (list var arg) bindings)
+ (setq i (1+ i)))))
+ ;; All args beyond the first are copyable: no temporary variables
+ ;; required.
+ (setq rev-args (reverse (cdr form))))
+ (let ((prev (car rev-args))
+ (exprs nil))
+ (dolist (arg (cdr rev-args))
+ (push (list op arg prev) exprs)
+ (setq prev arg))
+ (let ((and-expr (cons 'and exprs)))
+ (if bindings
+ (list 'let (nreverse bindings) and-expr)
+ and-expr)))))
+ (t form))))
+
(defun byte-optimize-constant-args (form)
(let ((ok t)
(rest (cdr form)))
@@ -1130,13 +1167,18 @@ See Info node `(elisp) Integer Basics'."
(put 'max 'byte-optimizer #'byte-optimize-min-max)
(put 'min 'byte-optimizer #'byte-optimize-min-max)
-(put '= 'byte-optimizer #'byte-optimize-binary-predicate)
(put 'eq 'byte-optimizer #'byte-optimize-eq)
(put 'eql 'byte-optimizer #'byte-optimize-equal)
(put 'equal 'byte-optimizer #'byte-optimize-equal)
(put 'string= 'byte-optimizer #'byte-optimize-binary-predicate)
(put 'string-equal 'byte-optimizer #'byte-optimize-binary-predicate)
+(put '= 'byte-optimizer #'byte-opt--nary-comparison)
+(put '< 'byte-optimizer #'byte-opt--nary-comparison)
+(put '<= 'byte-optimizer #'byte-opt--nary-comparison)
+(put '> 'byte-optimizer #'byte-opt--nary-comparison)
+(put '>= 'byte-optimizer #'byte-opt--nary-comparison)
+
(put 'string-greaterp 'byte-optimizer #'byte-optimize-string-greaterp)
(put 'string> 'byte-optimizer #'byte-optimize-string-greaterp)
diff --git a/lisp/emacs-lisp/bytecomp.el b/lisp/emacs-lisp/bytecomp.el
index aa9521e5a65..bfb9be4712b 100644
--- a/lisp/emacs-lisp/bytecomp.el
+++ b/lisp/emacs-lisp/bytecomp.el
@@ -3748,7 +3748,7 @@ If it is nil, then the handler is
\"byte-compile-SYMBOL.\""
'((0 . byte-compile-no-args)
(1 . byte-compile-one-arg)
(2 . byte-compile-two-args)
- (2-and . byte-compile-and-folded)
+ (2-cmp . byte-compile-cmp)
(3 . byte-compile-three-args)
(0-1 . byte-compile-zero-or-one-arg)
(1-2 . byte-compile-one-or-two-args)
@@ -3827,11 +3827,11 @@ If it is nil, then the handler is
\"byte-compile-SYMBOL.\""
(byte-defop-compiler cons 2)
(byte-defop-compiler aref 2)
(byte-defop-compiler set 2)
-(byte-defop-compiler (= byte-eqlsign) 2-and)
-(byte-defop-compiler (< byte-lss) 2-and)
-(byte-defop-compiler (> byte-gtr) 2-and)
-(byte-defop-compiler (<= byte-leq) 2-and)
-(byte-defop-compiler (>= byte-geq) 2-and)
+(byte-defop-compiler (= byte-eqlsign) 2-cmp)
+(byte-defop-compiler (< byte-lss) 2-cmp)
+(byte-defop-compiler (> byte-gtr) 2-cmp)
+(byte-defop-compiler (<= byte-leq) 2-cmp)
+(byte-defop-compiler (>= byte-geq) 2-cmp)
(byte-defop-compiler get 2)
(byte-defop-compiler nth 2)
(byte-defop-compiler substring 1-3)
@@ -3895,18 +3895,20 @@ If it is nil, then the handler is
\"byte-compile-SYMBOL.\""
(byte-compile-form (nth 2 form))
(byte-compile-out (get (car form) 'byte-opcode) 0)))
-(defun byte-compile-and-folded (form)
- "Compile calls to functions like `<='.
-These implicitly `and' together a bunch of two-arg bytecodes."
- (let ((l (length form)))
- (cond
- ((< l 3) (byte-compile-form `(progn ,(nth 1 form) t)))
- ((= l 3) (byte-compile-two-args form))
- ;; Don't use `cl-every' here (see comment where we require cl-lib).
- ((not (memq nil (mapcar #'macroexp-copyable-p (nthcdr 2 form))))
- (byte-compile-form `(and (,(car form) ,(nth 1 form) ,(nth 2 form))
- (,(car form) ,@(nthcdr 2 form)))))
- (t (byte-compile-normal-call form)))))
+(defun byte-compile-cmp (form)
+ "Compile calls to numeric comparisons such as `<', `=' etc."
+ ;; Lisp-level transforms should already have reduced valid calls to 2 args.
+ (if (not (= (length form) 3))
+ (byte-compile-subr-wrong-args form "1 or more")
+ (byte-compile-two-args
+ (if (macroexp-const-p (nth 1 form))
+ ;; First argument is constant: flip it so that the constant
+ ;; is last, which may allow more lapcode optimisations.
+ (let* ((op (car form))
+ (flipped-op (cdr (assq op '((< . >) (<= . >=)
+ (> . <) (>= . <=) (= . =))))))
+ (list flipped-op (nth 2 form) (nth 1 form)))
+ form))))
(defun byte-compile-three-args (form)
(if (not (= (length form) 4))