Optimize RESTART-CASE.
[sbcl.git] / src / code / defboot.lisp
index a5e7ba0..c3bb341 100644 (file)
@@ -41,7 +41,7 @@
     (if (= (length vars) 1)
       `(let ((,(car vars) ,value-form))
          ,@body)
-      (let ((ignore (gensym)))
+      (let ((ignore (sb!xc:gensym)))
         `(multiple-value-call #'(lambda (&optional ,@(mapcar #'list vars)
                                          &rest ,ignore)
                                   (declare (ignore ,ignore))
@@ -69,7 +69,8 @@
 (defmacro-mundanely cond (&rest clauses)
   (if (endp clauses)
       nil
-      (let ((clause (first clauses)))
+      (let ((clause (first clauses))
+            (more (rest clauses)))
         (if (atom clause)
             (error "COND clause is not a list: ~S" clause)
             (let ((test (first clause))
                     `(let ((,n-result ,test))
                        (if ,n-result
                            ,n-result
-                           (cond ,@(rest clauses)))))
-                  `(if ,test
-                       (progn ,@forms)
-                       (cond ,@(rest clauses)))))))))
+                           (cond ,@more))))
+                  (if (eq t test)
+                      ;; THE to perserve non-toplevelness for FOO in
+                      ;;   (COND (T (FOO)))
+                      `(the t (progn ,@forms))
+                      `(if ,test
+                           (progn ,@forms)
+                           ,(when more `(cond ,@more))))))))))
 
-;;; other things defined in terms of COND
 (defmacro-mundanely when (test &body forms)
   #!+sb-doc
   "If the first argument is true, the rest of the forms are
-  evaluated as a PROGN."
-  `(cond (,test nil ,@forms)))
+evaluated as a PROGN."
+  `(if ,test (progn ,@forms) nil))
+
 (defmacro-mundanely unless (test &body forms)
   #!+sb-doc
   "If the first argument is not true, the rest of the forms are
-  evaluated as a PROGN."
-  `(cond ((not ,test) nil ,@forms)))
+evaluated as a PROGN."
+  `(if ,test nil (progn ,@forms)))
+
 (defmacro-mundanely and (&rest forms)
   (cond ((endp forms) t)
-        ((endp (rest forms)) (first forms))
+        ((endp (rest forms))
+         ;; Preserve non-toplevelness of the form!
+         `(the t ,(first forms)))
         (t
          `(if ,(first forms)
               (and ,@(rest forms))
               nil))))
+
 (defmacro-mundanely or (&rest forms)
   (cond ((endp forms) nil)
-        ((endp (rest forms)) (first forms))
+        ((endp (rest forms))
+         ;; Preserve non-toplevelness of the form!
+         `(the t ,(first forms)))
         (t
          (let ((n-result (gensym)))
            `(let ((,n-result ,(first forms)))
 (defun inline-fun-name-p (name)
   (or
    ;; the normal reason for saving the inline expansion
-   (info :function :inlinep name)
+   (let ((inlinep (info :function :inlinep name)))
+     (member inlinep '(:inline :maybe-inline)))
    ;; another reason for saving the inline expansion: If the
    ;; ANSI-recommended idiom
    ;;   (DECLAIM (INLINE FOO))
 
 #-sb-xc-host
 (defun %defun (name def doc inline-lambda source-location)
-  (declare (ignore source-location))
   (declare (type function def))
   (declare (type (or null simple-string) doc))
   (aver (legal-fun-name-p name)) ; should've been checked by DEFMACRO DEFUN
   (sb!c:%compiler-defun name inline-lambda nil)
   (when (fboundp name)
     (/show0 "redefining NAME in %DEFUN")
-    (style-warn "redefining ~S in DEFUN" name))
+    (warn 'sb!kernel::redefinition-with-defun
+          :name name
+          :new-function def
+          :new-location source-location))
   (setf (sb!xc:fdefinition name) def)
+  ;; %COMPILER-DEFUN doesn't do this except at compile-time, when it
+  ;; also checks package locks. By doing this here we let (SETF
+  ;; FDEFINITION) do the load-time package lock checking before
+  ;; we frob any existing inline expansions.
+  (sb!c::%set-inline-expansion name nil inline-lambda)
 
-  ;; FIXME: I want to do this here (and fix bug 137), but until the
-  ;; breathtaking CMU CL function name architecture is converted into
-  ;; something sane, (1) doing so doesn't really fix the bug, and
-  ;; (2) doing probably isn't even really safe.
-  #+nil (setf (%fun-name def) name)
+  (sb!c::note-name-defined name :function)
 
   (when doc
-    (setf (fdocumentation name 'function) doc)
-    #!+sb-eval
-    (when (typep def 'sb!eval:interpreted-function)
-      (setf (sb!eval:interpreted-function-documentation def)
-            doc)))
+    (setf (%fun-doc def) doc))
+
   name)
 \f
 ;;;; DEFVAR and DEFPARAMETER
 
 (defmacro-mundanely defvar (var &optional (val nil valp) (doc nil docp))
   #!+sb-doc
-  "Define a global variable at top level. Declare the variable
+  "Define a special variable at top level. Declare the variable
   SPECIAL and, optionally, initialize it. If the variable already has a
   value, the old value is not clobbered. The third argument is an optional
   documentation string for the variable."
 ;;; ASAP, at the cost of being unable to use the standard
 ;;; destructuring mechanisms.
 (defmacro-mundanely dotimes ((var count &optional (result nil)) &body body)
-  (cond ((numberp count)
-         `(do ((,var 0 (1+ ,var)))
-              ((>= ,var ,count) ,result)
-            (declare (type unsigned-byte ,var))
-            ,@body))
-        (t (let ((v1 (gensym)))
-             `(do ((,var 0 (1+ ,var)) (,v1 ,count))
-                  ((>= ,var ,v1) ,result)
-                (declare (type unsigned-byte ,var))
-                ,@body)))))
-
-(defun filter-dolist-declarations (decls)
-  (mapcar (lambda (decl)
-            `(declare ,@(remove-if
-                         (lambda (clause)
-                           (and (consp clause)
-                                (or (eq (car clause) 'type)
-                                    (eq (car clause) 'ignore))))
-                         (cdr decl))))
-          decls))
-
-(defmacro-mundanely dolist ((var list &optional (result nil)) &body body)
+  (cond ((integerp count)
+        `(do ((,var 0 (1+ ,var)))
+             ((>= ,var ,count) ,result)
+           (declare (type unsigned-byte ,var))
+           ,@body))
+        (t
+         (let ((c (gensym "COUNT")))
+           `(do ((,var 0 (1+ ,var))
+                 (,c ,count))
+                ((>= ,var ,c) ,result)
+              (declare (type unsigned-byte ,var)
+                       (type integer ,c))
+              ,@body)))))
+
+(defmacro-mundanely dolist ((var list &optional (result nil)) &body body &environment env)
   ;; We repeatedly bind the var instead of setting it so that we never
   ;; have to give the var an arbitrary value such as NIL (which might
   ;; conflict with a declaration). If there is a result form, we
   ;; since we don't want to use IGNORABLE on what might be a special
   ;; var.
   (multiple-value-bind (forms decls) (parse-body body :doc-string-allowed nil)
-    (let ((n-list (gensym "N-LIST"))
-          (start (gensym "START")))
-      `(block nil
-         (let ((,n-list ,list))
-           (tagbody
-              ,start
-              (unless (endp ,n-list)
-                (let ((,var (car ,n-list)))
-                  ,@decls
-                  (setq ,n-list (cdr ,n-list))
-                  (tagbody ,@forms))
-                (go ,start))))
-         ,(if result
-              `(let ((,var nil))
-                 ;; Filter out TYPE declarations (VAR gets bound to NIL,
-                 ;; and might have a conflicting type declaration) and
-                 ;; IGNORE (VAR might be ignored in the loop body, but
-                 ;; it's used in the result form).
-                 ,@(filter-dolist-declarations decls)
-                 ,var
-                 ,result)
-               nil)))))
+    (let* ((n-list (gensym "N-LIST"))
+           (start (gensym "START")))
+      (multiple-value-bind (clist members clist-ok)
+          (cond ((sb!xc:constantp list env)
+                 (let ((value (constant-form-value list env)))
+                   (multiple-value-bind (all dot) (list-members value :max-length 20)
+                     (when (eql dot t)
+                       ;; Full warning is too much: the user may terminate the loop
+                       ;; early enough. Contents are still right, though.
+                       (style-warn "Dotted list ~S in DOLIST." value))
+                     (if (eql dot :maybe)
+                         (values value nil nil)
+                         (values value all t)))))
+                ((and (consp list) (eq 'list (car list))
+                      (every (lambda (arg) (sb!xc:constantp arg env)) (cdr list)))
+                 (let ((values (mapcar (lambda (arg) (constant-form-value arg env)) (cdr list))))
+                   (values values values t)))
+                (t
+                 (values nil nil nil)))
+        `(block nil
+           (let ((,n-list ,(if clist-ok (list 'quote clist) list)))
+             (tagbody
+                ,start
+                (unless (endp ,n-list)
+                  (let ((,var ,(if clist-ok
+                                   `(truly-the (member ,@members) (car ,n-list))
+                                   `(car ,n-list))))
+                    ,@decls
+                    (setq ,n-list (cdr ,n-list))
+                    (tagbody ,@forms))
+                  (go ,start))))
+           ,(if result
+                `(let ((,var nil))
+                   ;; Filter out TYPE declarations (VAR gets bound to NIL,
+                   ;; and might have a conflicting type declaration) and
+                   ;; IGNORE (VAR might be ignored in the loop body, but
+                   ;; it's used in the result form).
+                   ,@(filter-dolist-declarations decls)
+                   ,var
+                   ,result)
+                nil))))))
 \f
 ;;;; conditions, handlers, restarts
 
 ;;; KLUDGE: we PROCLAIM these special here so that we can use restart
 ;;; macros in the compiler before the DEFVARs are compiled.
-(sb!xc:proclaim
- '(special *handler-clusters* *restart-clusters* *condition-restarts*))
+;;;
+;;; For an explanation of these data structures, see DEFVARs in
+;;; target-error.lisp.
+(sb!xc:proclaim '(special *handler-clusters* *restart-clusters*))
 
 (defmacro-mundanely with-condition-restarts
     (condition-form restarts-form &body body)
    RESTARTS-FORM are associated with the condition returned by CONDITION-FORM.
    This allows FIND-RESTART, etc., to recognize restarts that are not related
    to the error currently being debugged. See also RESTART-CASE."
-  (let ((n-cond (gensym)))
-    `(let ((*condition-restarts*
-            (cons (let ((,n-cond ,condition-form))
-                    (cons ,n-cond
-                          (append ,restarts-form
-                                  (cdr (assoc ,n-cond *condition-restarts*)))))
-                  *condition-restarts*)))
-       ,@body)))
+  (once-only ((restarts restarts-form))
+    (with-unique-names (restart)
+      ;; FIXME: check the need for interrupt-safety.
+      `(unwind-protect
+           (progn
+             (dolist (,restart ,restarts)
+               (push ,condition-form
+                     (restart-associated-conditions ,restart)))
+             ,@body)
+         (dolist (,restart ,restarts)
+           (pop (restart-associated-conditions ,restart)))))))
 
 (defmacro-mundanely restart-bind (bindings &body forms)
   #!+sb-doc
-  "Executes forms in a dynamic context where the given restart bindings are
-   in effect. Users probably want to use RESTART-CASE. When clauses contain
-   the same restart name, FIND-RESTART will find the first such clause."
-  `(let ((*restart-clusters*
-          (cons (list
-                 ,@(mapcar (lambda (binding)
-                             (unless (or (car binding)
-                                         (member :report-function
-                                                 binding
-                                                 :test #'eq))
-                               (warn "Unnamed restart does not have a ~
-                                      report function: ~S"
-                                     binding))
-                             `(make-restart :name ',(car binding)
-                                            :function ,(cadr binding)
-                                            ,@(cddr binding)))
-                           bindings))
-                *restart-clusters*)))
-     ,@forms))
+  "(RESTART-BIND ({(case-name function {keyword value}*)}*) forms)
+   Executes forms in a dynamic context where the given bindings are in
+   effect. Users probably want to use RESTART-CASE. A case-name of NIL
+   indicates an anonymous restart. When bindings contain the same
+   restart name, FIND-RESTART will find the first such binding."
+  (flet ((parse-binding (binding)
+           (unless (>= (length binding) 2)
+             (error "ill-formed restart binding: ~S" binding))
+           (destructuring-bind (name function
+                                &rest args
+                                &key report-function &allow-other-keys)
+               binding
+             (unless (or name report-function)
+               (warn "Unnamed restart does not have a report function: ~
+                      ~S" binding))
+             `(make-restart :name ',name :function ,function ,@args))))
+    `(let ((*restart-clusters*
+             (cons (list ,@(mapcar #'parse-binding bindings))
+                   *restart-clusters*)))
+       ,@forms)))
 
 ;;; Wrap the RESTART-CASE expression in a WITH-CONDITION-RESTARTS if
 ;;; appropriate. Gross, but it's what the book seems to say...
 (defun munge-restart-case-expression (expression env)
-  (let ((exp (sb!xc:macroexpand expression env)))
+  (let ((exp (%macroexpand expression env)))
     (if (consp exp)
         (let* ((name (car exp))
                (args (if (eq name 'cerror) (cddr exp) (cdr exp))))
               expression))
         expression)))
 
-;;; FIXME: I did a fair amount of rearrangement of this code in order to
-;;; get WITH-KEYWORD-PAIRS to work cleanly. This code should be tested..
 (defmacro-mundanely restart-case (expression &body clauses &environment env)
   #!+sb-doc
-  "(RESTART-CASE form
-   {(case-name arg-list {keyword value}* body)}*)
-   The form is evaluated in a dynamic context where the clauses have special
-   meanings as points to which control may be transferred (see INVOKE-RESTART).
-   When clauses contain the same case-name, FIND-RESTART will find the first
-   such clause. If Expression is a call to SIGNAL, ERROR, CERROR or WARN (or
-   macroexpands into such) then the signalled condition will be associated with
-   the new restarts."
-  (flet ((transform-keywords (&key report interactive test)
-           (let ((result '()))
-             (when report
-               (setq result (list* (if (stringp report)
+  "(RESTART-CASE form {(case-name arg-list {keyword value}* body)}*)
+   The form is evaluated in a dynamic context where the clauses have
+   special meanings as points to which control may be transferred (see
+   INVOKE-RESTART).  When clauses contain the same case-name,
+   FIND-RESTART will find the first such clause. If form is a call to
+   SIGNAL, ERROR, CERROR or WARN (or macroexpands into such) then the
+   signalled condition will be associated with the new restarts."
+  ;; PARSE-CLAUSE (which uses PARSE-KEYWORDS-AND-BODY) is used to
+  ;; parse all clauses into lists of the form
+  ;;
+  ;;  (NAME TAG KEYWORDS LAMBDA-LIST BODY)
+  ;;
+  ;; where KEYWORDS are suitable keywords for use in HANDLER-BIND
+  ;; bindings. These lists are then passed to
+  ;; * MAKE-BINDING which generates bindings for the respective NAME
+  ;;   for HANDLER-BIND
+  ;; * MAKE-APPLY-AND-RETURN which generates TAGBODY entries executing
+  ;;   the respective BODY.
+  (let ((block-tag (sb!xc:gensym "BLOCK"))
+        (temp-var (gensym)))
+    (labels ((parse-keywords-and-body (keywords-and-body)
+               (do ((form keywords-and-body (cddr form))
+                    (result '())) (nil)
+                 (destructuring-bind (&optional key (arg nil argp) &rest rest)
+                     form
+                   (declare (ignore rest))
+                   (setq result
+                         (append
+                          (cond
+                            ((and (eq key :report) argp)
+                             (list :report-function
+                                   (if (stringp arg)
                                        `#'(lambda (stream)
-                                            (write-string ,report stream))
-                                       `#',report)
-                                   :report-function
-                                   result)))
-             (when interactive
-               (setq result (list* `#',interactive
-                                   :interactive-function
-                                   result)))
-             (when test
-               (setq result (list* `#',test :test-function result)))
-             (nreverse result)))
-         (parse-keyword-pairs (list keys)
-           (do ((l list (cddr l))
-                (k '() (list* (cadr l) (car l) k)))
-               ((or (null l) (not (member (car l) keys)))
-                (values (nreverse k) l)))))
-    (let ((block-tag (gensym))
-          (temp-var (gensym))
-          (data
-           (macrolet (;; KLUDGE: This started as an old DEFMACRO
-                      ;; WITH-KEYWORD-PAIRS general utility, which was used
-                      ;; only in this one place in the code. It was translated
-                      ;; literally into this MACROLET in order to avoid some
-                      ;; cross-compilation bootstrap problems. It would almost
-                      ;; certainly be clearer, and it would certainly be more
-                      ;; concise, to do a more idiomatic translation, merging
-                      ;; this with the TRANSFORM-KEYWORDS logic above.
-                      ;;   -- WHN 19990925
-                      (with-keyword-pairs ((names expression) &body forms)
-                        (let ((temp (member '&rest names)))
-                          (unless (= (length temp) 2)
-                            (error "&REST keyword is ~:[missing~;misplaced~]."
-                                   temp))
-                          (let* ((key-vars (ldiff names temp))
-                                 (keywords (mapcar #'keywordicate key-vars))
-                                 (key-var (gensym))
-                                 (rest-var (cadr temp)))
-                            `(multiple-value-bind (,key-var ,rest-var)
-                                 (parse-keyword-pairs ,expression ',keywords)
-                               (let ,(mapcar (lambda (var keyword)
-                                               `(,var (getf ,key-var
-                                                            ,keyword)))
-                                             key-vars keywords)
-                                 ,@forms))))))
-             (mapcar (lambda (clause)
-                       (with-keyword-pairs ((report interactive test
-                                                    &rest forms)
-                                            (cddr clause))
-                         (list (car clause) ;name=0
-                               (gensym) ;tag=1
-                               (transform-keywords :report report ;keywords=2
-                                                   :interactive interactive
-                                                   :test test)
-                               (cadr clause) ;bvl=3
-                               forms))) ;body=4
-                   clauses))))
-      `(block ,block-tag
-         (let ((,temp-var nil))
-           (tagbody
-            (restart-bind
-                ,(mapcar (lambda (datum)
-                           (let ((name (nth 0 datum))
-                                 (tag  (nth 1 datum))
-                                 (keys (nth 2 datum)))
-                             `(,name #'(lambda (&rest temp)
-                                         (setq ,temp-var temp)
-                                         (go ,tag))
-                                     ,@keys)))
-                         data)
-              (return-from ,block-tag
-                           ,(munge-restart-case-expression expression env)))
-            ,@(mapcan (lambda (datum)
-                        (let ((tag  (nth 1 datum))
-                              (bvl  (nth 3 datum))
-                              (body (nth 4 datum)))
-                          (list tag
-                                `(return-from ,block-tag
-                                   (apply (lambda ,bvl ,@body)
-                                          ,temp-var)))))
-                      data)))))))
+                                            (write-string ,arg stream))
+                                       `#',arg)))
+                            ((and (eq key :interactive) argp)
+                             (list :interactive-function `#',arg))
+                            ((and (eq key :test) argp)
+                             (list :test-function `#',arg))
+                            (t
+                             (return (values result form))))
+                          result)))))
+             (parse-clause (clause)
+               (unless (and (listp clause) (>= (length clause) 2)
+                            (listp (second clause)))
+                 (error "ill-formed ~S clause, no lambda-list:~%  ~S"
+                        'restart-case clause))
+               (destructuring-bind (name lambda-list &body body) clause
+                 (multiple-value-bind (keywords body)
+                     (parse-keywords-and-body body)
+                   (list name (sb!xc:gensym "TAG") keywords lambda-list body))))
+             (make-binding (clause-data)
+               (destructuring-bind (name tag keywords lambda-list body) clause-data
+                 (declare (ignore body))
+                 `(,name
+                   (lambda ,(cond ((null lambda-list)
+                                   ())
+                                  ((and (null (cdr lambda-list))
+                                        (not (member (car lambda-list)
+                                                     '(&optional &key &aux))))
+                                   '(temp))
+                                  (t
+                                   '(&rest temp)))
+                     ,@(when lambda-list `((setq ,temp-var temp)))
+                     (locally (declare (optimize (safety 0)))
+                       (go ,tag)))
+                   ,@keywords)))
+             (make-apply-and-return (clause-data)
+               (destructuring-bind (name tag keywords lambda-list body) clause-data
+                 (declare (ignore name keywords))
+                 `(,tag (return-from ,block-tag
+                          ,(cond ((null lambda-list)
+                                  `(progn ,@body))
+                                 ((and (null (cdr lambda-list))
+                                       (not (member (car lambda-list)
+                                                    '(&optional &key &aux))))
+                                  `(funcall (lambda ,lambda-list ,@body) ,temp-var))
+                                 (t
+                                  `(apply (lambda ,lambda-list ,@body) ,temp-var))))))))
+      (let ((clauses-data (mapcar #'parse-clause clauses)))
+        `(block ,block-tag
+           (let ((,temp-var nil))
+             (declare (ignorable ,temp-var))
+             (tagbody
+                (restart-bind
+                    ,(mapcar #'make-binding clauses-data)
+                  (return-from ,block-tag
+                    ,(munge-restart-case-expression expression env)))
+                ,@(mapcan #'make-apply-and-return clauses-data))))))))
 
 (defmacro-mundanely with-simple-restart ((restart-name format-string
                                                        &rest format-arguments)
                   (format stream ,format-string ,@format-arguments))
       (values nil t))))
 
-(defmacro-mundanely handler-bind (bindings &body forms)
-  #!+sb-doc
-  "(HANDLER-BIND ( {(type handler)}* )  body)
-   Executes body in a dynamic context where the given handler bindings are
-   in effect. Each handler must take the condition being signalled as an
-   argument. The bindings are searched first to last in the event of a
-   signalled condition."
+(defmacro-mundanely %handler-bind (bindings form)
   (let ((member-if (member-if (lambda (x)
                                 (not (proper-list-of-length-p x 2)))
                               bindings)))
     (when member-if
       (error "ill-formed handler binding: ~S" (first member-if))))
-  `(let ((*handler-clusters*
-          (cons (list ,@(mapcar (lambda (x) `(cons ',(car x) ,(cadr x)))
-                                bindings))
-                *handler-clusters*)))
-     (multiple-value-prog1
-         (progn
-           ,@forms)
-       ;; Wait for any float exceptions.
-       #!+x86 (float-wait))))
+  (let* ((local-funs nil)
+         (mapped-bindings (mapcar (lambda (binding)
+                                    (destructuring-bind (type handler) binding
+                                      (let ((lambda-form handler))
+                                        (if (and (consp handler)
+                                                 (or (eq 'lambda (car handler))
+                                                     (and (eq 'function (car handler))
+                                                          (consp (cdr handler))
+                                                          (let ((x (second handler)))
+                                                            (and (consp x)
+                                                                 (eq 'lambda (car x))
+                                                                 (setf lambda-form x))))))
+                                            (let ((name (sb!xc:gensym "LAMBDA")))
+                                              (push `(,name ,@(cdr lambda-form)) local-funs)
+                                              (list type `(function ,name)))
+                                            binding))))
+                                  bindings)))
+    `(dx-flet (,@(reverse local-funs))
+       (let ((*handler-clusters*
+              (cons (list ,@(mapcar (lambda (x) `(cons ',(car x) ,(cadr x)))
+                                    mapped-bindings))
+                    *handler-clusters*)))
+         #!+stack-allocatable-fixed-objects
+         (declare (truly-dynamic-extent *handler-clusters*))
+         (progn ,form)))))
+
+(defmacro-mundanely handler-bind (bindings &body forms)
+  #!+sb-doc
+  "(HANDLER-BIND ( {(type handler)}* )  body)
+
+Executes body in a dynamic context where the given handler bindings are in
+effect. Each handler must take the condition being signalled as an argument.
+The bindings are searched first to last in the event of a signalled
+condition."
+  `(%handler-bind ,bindings
+                  #!-x86 (progn ,@forms)
+                  ;; Need to catch FP errors here!
+                  #!+x86 (multiple-value-prog1 (progn ,@forms) (float-wait))))
 
 (defmacro-mundanely handler-case (form &rest cases)
-  "(HANDLER-CASE form
-   { (type ([var]) body) }* )
-   Execute FORM in a context with handlers established for the condition
-   types. A peculiar property allows type to be :NO-ERROR. If such a clause
-   occurs, and form returns normally, all its values are passed to this clause
-   as if by MULTIPLE-VALUE-CALL.  The :NO-ERROR clause accepts more than one
-   var specification."
-  ;; FIXME: Replacing CADR, CDDDR and friends with DESTRUCTURING-BIND
-  ;; and names for the subexpressions would make it easier to
-  ;; understand the code below.
+  "(HANDLER-CASE form { (type ([var]) body) }* )
+
+Execute FORM in a context with handlers established for the condition types. A
+peculiar property allows type to be :NO-ERROR. If such a clause occurs, and
+form returns normally, all its values are passed to this clause as if by
+MULTIPLE-VALUE-CALL. The :NO-ERROR clause accepts more than one var
+specification."
   (let ((no-error-clause (assoc ':no-error cases)))
     (if no-error-clause
         (let ((normal-return (make-symbol "normal-return"))
                  (return-from ,error-return
                    (handler-case (return-from ,normal-return ,form)
                      ,@(remove no-error-clause cases)))))))
-        (let ((tag (gensym))
-              (var (gensym))
-              (annotated-cases (mapcar (lambda (case) (cons (gensym) case))
-                                       cases)))
-          `(block ,tag
-             (let ((,var nil))
-               (declare (ignorable ,var))
-               (tagbody
-                (handler-bind
-                    ,(mapcar (lambda (annotated-case)
-                               (list (cadr annotated-case)
-                                     `(lambda (temp)
-                                        ,(if (caddr annotated-case)
-                                             `(setq ,var temp)
-                                             '(declare (ignore temp)))
-                                        (go ,(car annotated-case)))))
-                             annotated-cases)
-                  (return-from ,tag
-                    #!-x86 ,form
-                    #!+x86 (multiple-value-prog1 ,form
-                             ;; Need to catch FP errors here!
-                             (float-wait))))
-                ,@(mapcan
-                   (lambda (annotated-case)
-                     (list (car annotated-case)
-                           (let ((body (cdddr annotated-case)))
-                             `(return-from
-                                  ,tag
-                                ,(cond ((caddr annotated-case)
-                                        `(let ((,(caaddr annotated-case)
-                                                ,var))
-                                           ,@body))
-                                       (t
-                                        `(locally ,@body)))))))
-                   annotated-cases))))))))
+        (let* ((local-funs nil)
+               (annotated-cases
+                (mapcar (lambda (case)
+                          (with-unique-names (tag fun)
+                            (destructuring-bind (type ll &body body) case
+                              (push `(,fun ,ll ,@body) local-funs)
+                              (list tag type ll fun))))
+                        cases)))
+          (with-unique-names (block cell form-fun)
+            `(dx-flet ((,form-fun ()
+                         #!-x86 ,form
+                         ;; Need to catch FP errors here!
+                         #!+x86 (multiple-value-prog1 ,form (float-wait)))
+                       ,@(reverse local-funs))
+               (declare (optimize (sb!c::check-tag-existence 0)))
+               (block ,block
+                 ;; KLUDGE: We use a dx CONS cell instead of just assigning to
+                 ;; the variable directly, so that we can stack allocate
+                 ;; robustly: dx value cells don't work quite right, and it is
+                 ;; possible to construct user code that should loop
+                 ;; indefinitely, but instead eats up some stack each time
+                 ;; around.
+                 (dx-let ((,cell (cons :condition nil)))
+                   (declare (ignorable ,cell))
+                   (tagbody
+                      (%handler-bind
+                       ,(mapcar (lambda (annotated-case)
+                                  (destructuring-bind (tag type ll fun-name) annotated-case
+                                    (declare (ignore fun-name))
+                                    (list type
+                                          `(lambda (temp)
+                                             ,(if ll
+                                                  `(setf (cdr ,cell) temp)
+                                                  '(declare (ignore temp)))
+                                             (go ,tag)))))
+                                annotated-cases)
+                       (return-from ,block (,form-fun)))
+                      ,@(mapcan
+                         (lambda (annotated-case)
+                           (destructuring-bind (tag type ll fun-name) annotated-case
+                             (declare (ignore type))
+                             (list tag
+                                   `(return-from ,block
+                                      ,(if ll
+                                           `(,fun-name (cdr ,cell))
+                                           `(,fun-name))))))
+                         annotated-cases))))))))))
 \f
 ;;;; miscellaneous