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Optimise away functions in for-effect context

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* 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.
This commit is contained in:
Mattias Engdegård 2022-06-26 18:46:13 +02:00
parent d3893d7e8e
commit f2a5d48e89
1 changed files with 17 additions and 17 deletions

34
lisp/emacs-lisp/byte-opt.el
View file

@ -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)))