From f2a5d48e89bc5611c9cc9aeb978faacee32de6c8 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Mattias=20Engdeg=C3=A5rd?= Date: Sun, 26 Jun 2022 18:46:13 +0200 Subject: [PATCH] Optimise away functions in for-effect context * lisp/emacs-lisp/byte-opt.el (byte-optimize-form-code-walker): Turn functions into nil when compiled for-effect since they have no side-effects on their own. This may enable further improvements such as the elimination of variable bindings. `unwind-protect` forms can be treated as plain function call at this point. In particular, their unwind function argument should be not optimised for effect since it's a function. --- lisp/emacs-lisp/byte-opt.el | 34 +++++++++++++++++----------------- 1 file changed, 17 insertions(+), 17 deletions(-) diff --git a/lisp/emacs-lisp/byte-opt.el b/lisp/emacs-lisp/byte-opt.el index 1a50c5a43af..a8741c53bbf 100644 --- a/lisp/emacs-lisp/byte-opt.el +++ b/lisp/emacs-lisp/byte-opt.el @@ -406,7 +406,7 @@ for speeding up processing.") (`(function . ,_) ;; This forms is compiled as constant or by breaking out ;; all the subexpressions and compiling them separately. - form) + (and (not for-effect) form)) (`(condition-case ,var ,exp . ,clauses) `(,fn ,var ;Not evaluated. @@ -422,15 +422,13 @@ for speeding up processing.") (byte-optimize-body (cdr clause) for-effect)))) clauses))) - (`(unwind-protect ,exp :fun-body ,f) - ;; The unwinding part of an unwind-protect is compiled (and thus - ;; optimized) as a top-level form, but run the optimizer for it here - ;; anyway for lexical variable usage and substitution. But the - ;; protected part has the same for-effect status as the - ;; unwind-protect itself. (The unwinding part is always for effect, - ;; but that isn't handled properly yet.) - (let ((bodyform (byte-optimize-form exp for-effect))) - `(,fn ,bodyform :fun-body ,(byte-optimize-form f nil)))) + ;; `unwind-protect' is a special form which here takes the shape + ;; (unwind-protect EXPR :fun-body UNWIND-FUN). + ;; We can treat it as if it were a plain function at this point, + ;; although there are specific optimisations possible. + ;; In particular, the return value of UNWIND-FUN is never used + ;; so its body should really be compiled for-effect, but we + ;; don't do that right now. (`(catch ,tag . ,exps) `(,fn ,(byte-optimize-form tag nil) @@ -438,13 +436,15 @@ for speeding up processing.") ;; Needed as long as we run byte-optimize-form after cconv. (`(internal-make-closure . ,_) - ;; Look up free vars and mark them to be kept, so that they - ;; won't be optimised away. - (dolist (var (caddr form)) - (let ((lexvar (assq var byte-optimize--lexvars))) - (when lexvar - (setcar (cdr lexvar) t)))) - form) + (and (not for-effect) + (progn + ;; Look up free vars and mark them to be kept, so that they + ;; won't be optimised away. + (dolist (var (caddr form)) + (let ((lexvar (assq var byte-optimize--lexvars))) + (when lexvar + (setcar (cdr lexvar) t)))) + form))) (`((lambda . ,_) . ,_) (let ((newform (macroexp--unfold-lambda form))) -- 2.39.5