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Optimise prog1 better

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Rewrite (prog1 CONST FORMS...) => (progn FORMS... CONST)
where CONST is a compile-time constant, because putting the value last
allows the lapcode peephole pass to do important improvements like
branch elimination.  Also use progn instead of prog1 for `ignore`.

* lisp/emacs-lisp/byte-opt.el (byte-optimize-form-code-walker):
New `prog1` and `ignore` transforms.
This commit is contained in:
Mattias Engdegård 2021-07-29 10:07:26 +02:00
parent 9a63338114
commit dc9e2a1749
1 changed files with 8 additions and 5 deletions
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13
lisp/emacs-lisp/byte-opt.el
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@ -452,10 +452,13 @@ Same format as `byte-optimize--lexvars', with shared structure and contents.")
(macroexp-progn (byte-optimize-body exps for-effect))
(byte-optimize-form (car exps) for-effect)))
(`(prog1 ,exp . ,exps)
(if exps
`(prog1 ,(byte-optimize-form exp for-effect)
. ,(byte-optimize-body exps t))
(byte-optimize-form exp for-effect)))
(let ((exp-opt (byte-optimize-form exp for-effect)))
(if exps
(let ((exps-opt (byte-optimize-body exps t)))
(if (macroexp-const-p exp-opt)
`(progn ,@exps-opt ,exp-opt)
`(prog1 ,exp-opt ,@exps-opt)))
exp-opt)))
(`(,(or `save-excursion `save-restriction `save-current-buffer) . ,exps)
;; Those subrs which have an implicit progn; it's not quite good
@ -572,7 +575,7 @@ Same format as `byte-optimize--lexvars', with shared structure and contents.")
;; computed for effect. We want to avoid the warnings
;; that might occur if they were treated that way.
;; However, don't actually bother calling `ignore'.
`(prog1 nil . ,(mapcar #'byte-optimize-form exps)))
`(progn ,@(mapcar #'byte-optimize-form exps) nil))
;; Needed as long as we run byte-optimize-form after cconv.
(`(internal-make-closure . ,_)