Fix variable aliasing bytecode miscompilation (bug#67116)
The compiler didn't cancel aliasing if the aliased variable was
modified in a variable binding in the same `let` that created
the alias. For example,
(let ((x A))
(let ((y x)
(z (setq x B)))
y))
would incorrectly substitute y->x in the body form despite x being
already modified at that point, which normally should have cancelled
the aliasing.
Bug reported by Alan Mackenzie.
* lisp/emacs-lisp/byte-opt.el (byte-optimize--aliased-vars):
Now an alist that also contains the aliases; update the doc string.
* lisp/emacs-lisp/byte-opt.el (byte-optimize-form-code-walker):
* lisp/emacs-lisp/byte-opt.el (byte-optimize-let-form):
Detect aliasing early for `let`-bound variables as well.
* test/lisp/emacs-lisp/bytecomp-tests.el (bytecomp-tests--test-cases):
Add test cases.
This commit is contained in:
Mattias Engdegård
parent
8090ab0543
commit
1247dc87ba
2 changed files with 36 additions and 29 deletions
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@ -217,10 +217,10 @@ This indicates the loop discovery phase.")
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(defvar byte-optimize--aliased-vars nil
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"List of variables which may be aliased by other lexical variables.
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If an entry in `byte-optimize--lexvars' has another variable as its VALUE,
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then that other variable must be in this list.
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This variable thus carries no essential information but is maintained
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for speeding up processing.")
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Each element is (NAME . ALIAS) where NAME is the aliased variable
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and ALIAS the variable record (in the format described for
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`byte-optimize--lexvars') for an alias, which may have NAME as its VALUE.
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There can be multiple entries for the same NAME if it has several aliases.")
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(defun byte-optimize--substitutable-p (expr)
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"Whether EXPR is a constant that can be propagated."
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@ -462,13 +462,17 @@ for speeding up processing.")
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(setcar (cdr lexvar) t) ; Mark variable to be kept.
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(setcdr (cdr lexvar) nil) ; Inhibit further substitution.
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(when (memq var byte-optimize--aliased-vars)
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;; Cancel aliasing of variables aliased to this one.
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(dolist (v byte-optimize--lexvars)
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(when (eq (nth 2 v) var)
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;; V is bound to VAR but VAR is now mutated:
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;; cancel aliasing.
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(setcdr (cdr v) nil)))))
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;; Cancel substitution of variables aliasing this one.
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(let ((aliased-vars byte-optimize--aliased-vars))
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(while
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(let ((alias (assq var aliased-vars)))
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(and alias
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(progn
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;; Found a variable bound to VAR but VAR is
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;; now mutated; cancel aliasing.
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(setcdr (cddr alias) nil)
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(setq aliased-vars (cdr (memq alias aliased-vars)))
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t))))))
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`(,fn ,var ,value)))
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(`(defvar ,(and (pred symbolp) name) . ,rest)
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@ -587,7 +591,6 @@ for speeding up processing.")
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(let* ((byte-optimize--lexvars byte-optimize--lexvars)
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(byte-optimize--aliased-vars byte-optimize--aliased-vars)
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(new-lexvars nil)
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(new-aliased-vars nil)
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(let-vars nil)
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(body (cdr form))
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(bindings (car form)))
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@ -597,7 +600,7 @@ for speeding up processing.")
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(expr (byte-optimize-form (cadr binding) nil)))
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(setq bindings (cdr bindings))
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(when (and (eq head 'let*)
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(memq name byte-optimize--aliased-vars))
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(assq name byte-optimize--aliased-vars))
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;; New variable shadows an aliased variable -- α-rename
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;; it in this and all subsequent bindings.
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(let ((new-name (make-symbol (symbol-name name))))
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@ -610,14 +613,12 @@ for speeding up processing.")
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bindings))
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(setq body (byte-optimize--rename-var-body name new-name body))
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(setq name new-name)))
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(let* ((aliased nil)
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(value (and
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(or (byte-optimize--substitutable-p expr)
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;; Aliasing another lexvar.
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(setq aliased
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(and (symbolp expr)
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(assq expr byte-optimize--lexvars))))
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(list expr)))
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(let* ((aliased
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;; Aliasing another lexvar.
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(and (symbolp expr) (assq expr byte-optimize--lexvars)))
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(value (and (or aliased
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(byte-optimize--substitutable-p expr))
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(list expr)))
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(lexical (not (or (special-variable-p name)
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(memq name byte-compile-bound-variables)
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(memq name byte-optimize--dynamic-vars))))
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@ -626,20 +627,16 @@ for speeding up processing.")
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(when lexinfo
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(push lexinfo (if (eq head 'let*)
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byte-optimize--lexvars
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new-lexvars)))
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(when aliased
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(push expr (if (eq head 'let*)
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byte-optimize--aliased-vars
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new-aliased-vars))))))
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new-lexvars))
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(when aliased
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(push (cons expr lexinfo) byte-optimize--aliased-vars))))))
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(setq byte-optimize--aliased-vars
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(append new-aliased-vars byte-optimize--aliased-vars))
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(when (and (eq head 'let) byte-optimize--aliased-vars)
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;; Find new variables that shadow aliased variables.
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(let ((shadowing-vars nil))
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(dolist (lexvar new-lexvars)
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(let ((name (car lexvar)))
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(when (and (memq name byte-optimize--aliased-vars)
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(when (and (assq name byte-optimize--aliased-vars)
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(not (memq name shadowing-vars)))
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(push name shadowing-vars))))
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;; α-rename them
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@ -643,6 +643,16 @@ inner loops respectively."
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(funcall (car f) 3)
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(list a b))
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(let ((x (list 1)))
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(let ((y x)
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(z (setq x (vector x))))
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(list x y z)))
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(let ((x (list 1)))
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(let* ((y x)
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(z (setq x (vector x))))
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(list x y z)))
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(cond)
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(mapcar (lambda (x) (cond ((= x 0)))) '(0 1))
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