Commit d5ee655c authored by Stefan Monnier's avatar Stefan Monnier
Browse files

* lisp/emacs-lisp/macroexp.el: Tweak macroexp-if optimizations

(macroexp-unprogn): Make sure we never return an empty list.
(macroexp-if): Remove unused (and unsafe) optimization.
Optimize (if A T (if B T E)) into (if (or A B) T E) instead, which does
occur occasionally.
parent 1f02cbea
......@@ -322,8 +322,9 @@ definitions to shadow the loaded ones for use in file byte-compilation."
(if (cdr exps) `(progn ,@exps) (car exps)))
(defun macroexp-unprogn (exp)
"Turn EXP into a list of expressions to execute in sequence."
(if (eq (car-safe exp) 'progn) (cdr exp) (list exp)))
"Turn EXP into a list of expressions to execute in sequence.
Never returns an empty list."
(if (eq (car-safe exp) 'progn) (or (cdr exp) '(nil)) (list exp)))
(defun macroexp-let* (bindings exp)
"Return an expression equivalent to `(let* ,bindings ,exp)."
......@@ -333,22 +334,33 @@ definitions to shadow the loaded ones for use in file byte-compilation."
(t `(let* ,bindings ,exp))))
(defun macroexp-if (test then else)
"Return an expression equivalent to `(if ,test ,then ,else)."
"Return an expression equivalent to `(if ,TEST ,THEN ,ELSE)."
(cond
((eq (car-safe else) 'if)
(if (equal test (nth 1 else))
;; Doing a test a second time: get rid of the redundancy.
`(if ,test ,then ,@(nthcdr 3 else))
`(cond (,test ,then)
(,(nth 1 else) ,(nth 2 else))
(t ,@(nthcdr 3 else)))))
(cond
;; Drop this optimization: It's unsafe (it assumes that `test' is
;; pure, or at least idempotent), and it's not used even a single
;; time while compiling Emacs's sources.
;;((equal test (nth 1 else))
;; ;; Doing a test a second time: get rid of the redundancy.
;; (message "macroexp-if: sharing 'test' %S" test)
;; `(if ,test ,then ,@(nthcdr 3 else)))
((equal then (nth 2 else))
;; (message "macroexp-if: sharing 'then' %S" then)
`(if (or ,test ,(nth 1 else)) ,then ,@(nthcdr 3 else)))
((equal (macroexp-unprogn then) (nthcdr 3 else))
;; (message "macroexp-if: sharing 'then' with not %S" then)
`(if (or ,test (not ,(nth 1 else)))
,then ,@(macroexp-unprogn (nth 2 else))))
(t
`(cond (,test ,@(macroexp-unprogn then))
(,(nth 1 else) ,@(macroexp-unprogn (nth 2 else)))
(t ,@(nthcdr 3 else))))))
((eq (car-safe else) 'cond)
`(cond (,test ,then)
;; Doing a test a second time: get rid of the redundancy, as above.
,@(remove (assoc test else) (cdr else))))
`(cond (,test ,@(macroexp-unprogn then)) ,@(cdr else)))
;; Invert the test if that lets us reduce the depth of the tree.
((memq (car-safe then) '(if cond)) (macroexp-if `(not ,test) else then))
(t `(if ,test ,then ,else))))
(t `(if ,test ,then ,@(macroexp-unprogn else)))))
(defmacro macroexp-let2 (test sym exp &rest body)
"Evaluate BODY with SYM bound to an expression for EXP's value.
......
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