;;;; This file implements the stack analysis phase in the compiler. We
-;;;; do a graph walk to determine which unknown-values lvars are on
-;;;; the stack at each point in the program, and then we insert
-;;;; cleanup code to remove unused values.
+;;;; analyse lifetime of dynamically allocated object packets on stack
+;;;; and insert cleanups where necessary.
+;;;;
+;;;; Currently there are two kinds of interesting stack packets: UVLs,
+;;;; whose use and destination lie in different blocks, and LVARs of
+;;;; constructors of dynamic-extent objects.
;;;; This software is part of the SBCL system. See the README file for
;;;; more information.
;;; invariant that all pushes come after the last pop.
(defun find-pushed-lvars (block)
(let* ((2block (block-info block))
- (popped (ir2-block-popped 2block))
- (last-pop (if popped
- (lvar-dest (car (last popped)))
- nil)))
+ (popped (ir2-block-popped 2block))
+ (last-pop (if popped
+ (lvar-dest (car (last popped)))
+ nil)))
(collect ((pushed))
(let ((saw-last nil))
- (do-nodes (node lvar block)
- (when (eq node last-pop)
- (setq saw-last t))
+ (do-nodes (node lvar block)
+ (when (eq node last-pop)
+ (setq saw-last t))
- (when lvar
- (let ((dest (lvar-dest lvar))
- (2lvar (lvar-info lvar)))
- (when (and (not (eq (node-block dest) block))
- 2lvar
- (eq (ir2-lvar-kind 2lvar) :unknown))
- (aver (or saw-last (not last-pop)))
- (pushed lvar))))))
+ (when (and lvar
+ (or (lvar-dynamic-extent lvar)
+ (let ((dest (lvar-dest lvar))
+ (2lvar (lvar-info lvar)))
+ (and (not (eq (node-block dest) block))
+ 2lvar
+ (eq (ir2-lvar-kind 2lvar) :unknown)))))
+ (aver (or saw-last (not last-pop)))
+ (pushed lvar))))
(setf (ir2-block-pushed 2block) (pushed))))
(values))
;;; been changed.
(defun merge-uvl-live-sets (early late)
(declare (type list early late))
+ ;; FIXME: O(N^2)
(dolist (e late early)
(pushnew e early)))
nle-start-stack)))
(setq new-end (merge-uvl-live-sets
new-end next-stack))))
- block)
+ block
+ (lambda (dx-cleanup)
+ (dolist (lvar (cleanup-info dx-cleanup))
+ (do-uses (generator lvar)
+ (let* ((block (node-block generator))
+ (2block (block-info block)))
+ ;; DX objects, living in the LVAR, are alive in
+ ;; the environment, protected by the CLEANUP. We
+ ;; also cannot move them (because, in general, we
+ ;; cannot track all references to them).
+ ;; Therefore, everything, allocated deeper than a
+ ;; DX object -- that is, before the DX object --
+ ;; should be kept alive until the object is
+ ;; deallocated.
+ ;;
+ ;; Since DX generators end their blocks, we can
+ ;; find out UVLs allocated before them by looking
+ ;; at the stack at the end of the block.
+ ;;
+ ;; FIXME: This is not quite true: REFs to DX
+ ;; closures don't end their blocks!
+ (setq new-end (merge-uvl-live-sets
+ new-end (ir2-block-end-stack 2block)))
+ (setq new-end (merge-uvl-live-sets
+ new-end (ir2-block-pushed 2block))))))))
(setf (ir2-block-end-stack 2block) new-end)
;; We cannot delete unused UVLs during NLX, so all UVLs live at
;; ENTRY will be actually live at NLE.
+ ;;
+ ;; BUT, UNWIND-PROTECTor is called in the environment, which has
+ ;; nothing in common with the environment of its entry. So we
+ ;; fictively compute its stack from the containing cleanups, but
+ ;; do not propagate additional LVARs from the entry, thus
+ ;; preveting bogus stack cleanings.
+ ;;
+ ;; TODO: Insert a check that no values are discarded in UWP. Or,
+ ;; maybe, we just don't need to create NLX-ENTRY for UWP?
(when (and (eq (component-head (block-component block))
(first (block-pred block)))
(not (bind-p (block-start-node block))))
- (let* ((entry-block (nle-block-entry-block block))
- (entry-stack (ir2-block-start-stack (block-info entry-block))))
- (setq start (merge-uvl-live-sets start entry-stack))))
+ (let* ((nlx-info (nle-block-nlx-info block))
+ (cleanup (nlx-info-cleanup nlx-info)))
+ (unless (eq (cleanup-kind cleanup) :unwind-protect)
+ (let* ((entry-block (node-block (cleanup-mess-up cleanup)))
+ (entry-stack (ir2-block-start-stack (block-info entry-block))))
+ (setq start (merge-uvl-live-sets start entry-stack))))))
(when *check-consistency*
(aver (subsetp original-start start)))
(defun order-uvl-sets (component)
(clear-flags component)
+ ;; KLUDGE: Workaround for lp#308914: we keep track of number of blocks
+ ;; needing repeats, and bug out if we get stuck.
(loop with head = (component-head component)
- with repeat-p do
- (setq repeat-p nil)
- (do-blocks (block component)
- (unless (block-flag block)
- (let ((pred (find-if #'block-flag (block-pred block))))
- (when (and (eq pred head)
- (not (bind-p (block-start-node block))))
- (let ((entry (nle-block-entry-block block)))
- (setq pred (if (block-flag entry) entry nil))))
- (cond (pred
- (setf (block-flag block) t)
- (order-block-uvl-sets block pred))
- (t
- (setq repeat-p t))))))
- while repeat-p))
+ with todo = 0
+ with last-todo = 0
+ do (psetq last-todo todo
+ todo 0)
+ do (do-blocks (block component)
+ (unless (block-flag block)
+ (let ((pred (find-if #'block-flag (block-pred block))))
+ (when (and (eq pred head)
+ (not (bind-p (block-start-node block))))
+ (let ((entry (nle-block-entry-block block)))
+ (setq pred (if (block-flag entry) entry nil))))
+ (cond (pred
+ (setf (block-flag block) t)
+ (order-block-uvl-sets block pred))
+ (t
+ (incf todo))))))
+ do (when (= last-todo todo)
+ ;; If the todo count is the same as on last iteration, it means
+ ;; we are stuck, which in turn means the unmarked blocks are
+ ;; actually unreachable, so UVL set ordering for them doesn't
+ ;; matter.
+ (return-from order-uvl-sets))
+ while (plusp todo)))
\f
;;; This is called when we discover that the stack-top unknown-values
;;; lvar at the end of BLOCK1 is different from that at the start of
;;; wastes only space.
(defun discard-unused-values (block1 block2)
(declare (type cblock block1 block2))
- (let* ((block1-stack (ir2-block-end-stack (block-info block1)))
- (block2-stack (ir2-block-start-stack (block-info block2)))
- (cleanup-code
- (cond ((eq (car block1-stack) (car block2-stack))
- (binding* ((preserved-count (mismatch block1-stack block2-stack)
- :exit-if-null)
- (n-last-preserved (1- preserved-count))
- (nipped-count (- (length block1-stack)
- (length block2-stack)))
- (n-last-nipped (+ n-last-preserved nipped-count)))
- (aver (equal (nthcdr (1+ n-last-nipped) block1-stack)
- (nthcdr preserved-count block2-stack)))
- (compiler-notify "%NIP-VALUES emitted")
- `(%nip-values ',(elt block1-stack n-last-nipped)
- ',(elt block1-stack n-last-preserved)
- ,@(loop for moved in block1-stack
- repeat preserved-count
- collect `',moved))))
- (t
- (let* ((n-popped (- (length block1-stack)
- (length block2-stack)))
- (last-popped (elt block1-stack (1- n-popped))))
- (when *check-consistency*
- (aver (equal block2-stack (nthcdr n-popped block1-stack))))
- `(%pop-values ',last-popped))))))
- (when cleanup-code
+ (collect ((cleanup-code))
+ (labels ((find-popped (before after)
+ ;; Returns (VALUES popped last-popped rest), where
+ ;; BEFORE = (APPEND popped rest) and
+ ;; (EQ (FIRST rest) (FIRST after))
+ (if (null after)
+ (values before (first (last before)) nil)
+ (loop with first-preserved = (car after)
+ for last-popped = nil then maybe-popped
+ for rest on before
+ for maybe-popped = (car rest)
+ while (neq maybe-popped first-preserved)
+ collect maybe-popped into popped
+ finally (return (values popped last-popped rest)))))
+ (discard (before-stack after-stack)
+ (cond
+ ((eq (car before-stack) (car after-stack))
+ (binding* ((moved-count (mismatch before-stack after-stack)
+ :exit-if-null)
+ ((moved qmoved)
+ (loop for moved-lvar in before-stack
+ repeat moved-count
+ collect moved-lvar into moved
+ collect `',moved-lvar into qmoved
+ finally (return (values moved qmoved))))
+ (q-last-moved (car (last qmoved)))
+ ((nil last-nipped rest)
+ (find-popped (nthcdr moved-count before-stack)
+ (nthcdr moved-count after-stack))))
+ (cleanup-code
+ `(%nip-values ',last-nipped ,q-last-moved
+ ,@qmoved))
+ (discard (nconc moved rest) after-stack)))
+ (t
+ (multiple-value-bind (popped last-popped rest)
+ (find-popped before-stack after-stack)
+ (declare (ignore popped))
+ (cleanup-code `(%pop-values ',last-popped))
+ (discard rest after-stack))))))
+ (discard (ir2-block-end-stack (block-info block1))
+ (ir2-block-start-stack (block-info block2))))
+ (when (cleanup-code)
(let* ((block (insert-cleanup-code block1 block2
(block-start-node block2)
- cleanup-code))
+ `(progn ,@(cleanup-code))))
(2block (make-ir2-block block)))
(setf (block-info block) 2block)
(add-to-emit-order 2block (block-info block1))
;;;; stack analysis
;;; Return a list of all the blocks containing genuine uses of one of
-;;; the RECEIVERS. Exits are excluded, since they don't drop through
-;;; to the receiver.
-(defun find-values-generators (receivers)
- (declare (list receivers))
+;;; the RECEIVERS (blocks) and DX-LVARS. Exits are excluded, since
+;;; they don't drop through to the receiver.
+(defun find-pushing-blocks (receivers dx-lvars)
+ (declare (list receivers dx-lvars))
(collect ((res nil adjoin))
(dolist (rec receivers)
(dolist (pop (ir2-block-popped (block-info rec)))
- (do-uses (use pop)
- (unless (exit-p use)
- (res (node-block use))))))
+ (do-uses (use pop)
+ (unless (exit-p use)
+ (res (node-block use))))))
+ (dolist (dx-lvar dx-lvars)
+ (do-uses (use dx-lvar)
+ (res (node-block use))))
(res)))
-;;; Analyze the use of unknown-values lvars in COMPONENT, inserting
-;;; cleanup code to discard values that are generated but never
-;;; received. This phase doesn't need to be run when Values-Receivers
-;;; is null, i.e. there are no unknown-values lvars used across block
-;;; boundaries.
+;;; Analyze the use of unknown-values and DX lvars in COMPONENT,
+;;; inserting cleanup code to discard values that are generated but
+;;; never received. This phase doesn't need to be run when
+;;; Values-Receivers and Dx-Lvars are null, i.e. there are no
+;;; unknown-values lvars used across block boundaries and no DX LVARs.
(defun stack-analyze (component)
(declare (type component component))
(let* ((2comp (component-info component))
- (receivers (ir2-component-values-receivers 2comp))
- (generators (find-values-generators receivers)))
+ (receivers (ir2-component-values-receivers 2comp))
+ (generators (find-pushing-blocks receivers
+ (component-dx-lvars component))))
(dolist (block generators)
(find-pushed-lvars block))
- ;;; Compute sets of live UVLs
+ ;;; Compute sets of live UVLs and DX LVARs
(loop for did-something = nil
do (do-blocks-backwards (block component)
(when (update-uvl-live-sets block)
(do-blocks (block component)
(let ((top (ir2-block-end-stack (block-info block))))
- (dolist (succ (block-succ block))
- (when (and (block-start succ)
- (not (eq (ir2-block-start-stack (block-info succ))
- top)))
- (discard-unused-values block succ))))))
+ (dolist (succ (block-succ block))
+ (when (and (block-start succ)
+ (not (eq (ir2-block-start-stack (block-info succ))
+ top)))
+ (discard-unused-values block succ))))))
(values))
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