;;;; This file implements the stack analysis phase in the compiler. We
-;;;; do a graph walk to determine which unknown-values continuations
-;;;; are on the stack at each point in the program, and then we insert
-;;;; cleanup code to pop off 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.
(in-package "SB!C")
\f
-;;; Scan through Block looking for uses of :Unknown continuations that have
-;;; their Dest outside of the block. We do some checking to verify the
+;;; Scan through BLOCK looking for uses of :UNKNOWN lvars that have
+;;; their DEST outside of the block. We do some checking to verify the
;;; invariant that all pushes come after the last pop.
-(defun find-pushed-continuations (block)
+(defun find-pushed-lvars (block)
(let* ((2block (block-info block))
- (popped (ir2-block-popped 2block))
- (last-pop (if popped
- (continuation-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 cont block)
- (when (eq node last-pop)
- (setq saw-last t))
-
- (let ((dest (continuation-dest cont))
- (2cont (continuation-info cont)))
- (when (and dest
- (not (eq (node-block dest) block))
- 2cont
- (eq (ir2-continuation-kind 2cont) :unknown))
- (aver (or saw-last (not last-pop)))
- (pushed cont)))))
+ (do-nodes (node lvar block)
+ (when (eq node last-pop)
+ (setq saw-last t))
+
+ (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))
\f
-;;;; annotation graph walk
-
-;;; Do a backward walk in the flow graph simulating the run-time stack of
-;;; unknown-values continuations and annotating the blocks with the result.
-;;;
-;;; Block is the block that is currently being walked and Stack is the stack
-;;; of unknown-values continuations in effect immediately after block. We
-;;; simulate the stack by popping off the unknown-values generated by this
-;;; block (if any) and pushing the continuations for values received by this
-;;; block. (The role of push and pop are interchanged because we are doing a
-;;; backward walk.)
-;;;
-;;; If we run into a values generator whose continuation isn't on stack top,
-;;; then the receiver hasn't yet been reached on any walk to this use. In this
-;;; case, we ignore the push for now, counting on Annotate-Dead-Values to clean
-;;; it up if we discover that it isn't reachable at all.
-;;;
-;;; If our final stack isn't empty, then we walk all the predecessor blocks
-;;; that don't have all the continuations that we have on our Start-Stack on
-;;; their End-Stack. This is our termination condition for the graph walk. We
-;;; put the test around the recursive call so that the initial call to this
-;;; function will do something even though there isn't initially anything on
-;;; the stack.
-;;;
-;;; We can use the tailp test, since the only time we want to bottom out
-;;; with a non-empty stack is when we intersect with another path from the same
-;;; top-level call to this function that has more values receivers on that
-;;; path. When we bottom out in this way, we are counting on
-;;; DISCARD-UNUSED-VALUES doing its thing.
-;;;
-;;; When we do recurse, we check that predecessor's END-STACK is a
-;;; subsequence of our START-STACK. There may be extra stuff on the top
-;;; of our stack because the last path to the predecessor may have discarded
-;;; some values that we use. There may be extra stuff on the bottom of our
-;;; stack because this walk may be from a values receiver whose lifetime
-;;; encloses that of the previous walk.
-;;;
-;;; If a predecessor block is the component head, then it must be the case
-;;; that this is a NLX entry stub. If so, we just stop our walk, since the
-;;; stack at the exit point doesn't have anything to do with our stack.
-(defun stack-simulation-walk (block stack)
- (declare (type cblock block) (list stack))
- (let ((2block (block-info block)))
- (setf (ir2-block-end-stack 2block) stack)
- (let ((new-stack stack))
- (dolist (push (reverse (ir2-block-pushed 2block)))
- (if (eq (car new-stack) push)
- (pop new-stack)
- (aver (not (member push new-stack)))))
-
- (dolist (pop (reverse (ir2-block-popped 2block)))
- (push pop new-stack))
-
- (setf (ir2-block-start-stack 2block) new-stack)
-
- (when new-stack
- (dolist (pred (block-pred block))
- (if (eq pred (component-head (block-component block)))
- (aver (find block
- (environment-nlx-info (block-environment block))
- :key #'nlx-info-target))
- (let ((pred-stack (ir2-block-end-stack (block-info pred))))
- (unless (tailp new-stack pred-stack)
- (aver (search pred-stack new-stack))
- (stack-simulation-walk pred new-stack))))))))
+;;;; Computation of live UVL sets
+(defun nle-block-nlx-info (block)
+ (let* ((start-node (block-start-node block))
+ (nlx-ref (ctran-next (node-next start-node)))
+ (nlx-info (constant-value (ref-leaf nlx-ref))))
+ nlx-info))
+(defun nle-block-entry-block (block)
+ (let* ((nlx-info (nle-block-nlx-info block))
+ (mess-up (cleanup-mess-up (nlx-info-cleanup nlx-info)))
+ (entry-block (node-block mess-up)))
+ entry-block))
- (values))
+;;; Add LVARs from LATE to EARLY; use EQ to check whether EARLY has
+;;; 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)))
-;;; Do stack annotation for any values generators in Block that were
-;;; unreached by all walks (i.e. the continuation isn't live at the point that
-;;; it is generated.) This will only happen when the values receiver cannot be
-;;; reached from this particular generator (due to an unconditional control
-;;; transfer.)
-;;;
-;;; What we do is push on the End-Stack all continuations in Pushed that
-;;; aren't already present in the End-Stack. When we find any pushed
-;;; continuation that isn't live, it must be the case that all continuations
-;;; pushed after (on top of) it aren't live.
+;;; Update information on stacks of unknown-values LVARs on the
+;;; boundaries of BLOCK. Return true if the start stack has been
+;;; changed.
;;;
-;;; If we see a pushed continuation that is the CONT of a tail call, then we
-;;; ignore it, since the tail call didn't actually push anything. The tail
-;;; call must always the last in the block.
-(defun annotate-dead-values (block)
+;;; An LVAR is live at the end iff it is live at some of blocks, which
+;;; BLOCK can transfer control to. There are two kind of control
+;;; transfers: normal, expressed with BLOCK-SUCC, and NLX.
+(defun update-uvl-live-sets (block)
(declare (type cblock block))
(let* ((2block (block-info block))
- (stack (ir2-block-end-stack 2block))
- (last (block-last block))
- (tailp-cont (if (node-tail-p last) (node-cont last))))
- (do ((pushes (ir2-block-pushed 2block) (rest pushes))
- (popping nil))
- ((null pushes))
- (let ((push (first pushes)))
- (cond ((member push stack)
- (aver (not popping)))
- ((eq push tailp-cont)
- (aver (null (rest pushes))))
- (t
- (push push (ir2-block-end-stack 2block))
- (setq popping t))))))
+ (original-start (ir2-block-start-stack 2block))
+ (end (ir2-block-end-stack 2block))
+ (new-end end))
+ (dolist (succ (block-succ block))
+ (setq new-end (merge-uvl-live-sets new-end
+ (ir2-block-start-stack (block-info succ)))))
+ (map-block-nlxes (lambda (nlx-info)
+ (let* ((nle (nlx-info-target nlx-info))
+ (nle-start-stack (ir2-block-start-stack
+ (block-info nle)))
+ (exit-lvar (nlx-info-lvar nlx-info))
+ (next-stack (if exit-lvar
+ (remove exit-lvar nle-start-stack)
+ nle-start-stack)))
+ (setq new-end (merge-uvl-live-sets
+ new-end next-stack))))
+ 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)
+
+ (let ((start new-end))
+ (setq start (set-difference start (ir2-block-pushed 2block)))
+ (setq start (merge-uvl-live-sets start (ir2-block-popped 2block)))
+
+ ;; 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* ((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)))
+ (cond ((subsetp start original-start)
+ nil)
+ (t
+ (setf (ir2-block-start-stack 2block) start)
+ t)))))
- (values))
+\f
+;;;; Ordering of live UVL stacks
+
+;;; Put UVLs on the start/end stacks of BLOCK in the right order. PRED
+;;; is a predecessor of BLOCK with already sorted stacks; because all
+;;; UVLs being live at the BLOCK start are live in PRED, we just need
+;;; to delete dead UVLs.
+(defun order-block-uvl-sets (block pred)
+ (let* ((2block (block-info block))
+ (pred-end-stack (ir2-block-end-stack (block-info pred)))
+ (start (ir2-block-start-stack 2block))
+ (start-stack (loop for lvar in pred-end-stack
+ when (memq lvar start)
+ collect lvar))
+ (end (ir2-block-end-stack 2block)))
+ (when *check-consistency*
+ (aver (subsetp start start-stack)))
+ (setf (ir2-block-start-stack 2block) start-stack)
+
+ (let* ((last (block-last block))
+ (tailp-lvar (if (node-tail-p last) (node-lvar last)))
+ (end-stack start-stack))
+ (dolist (pop (ir2-block-popped 2block))
+ (aver (eq pop (car end-stack)))
+ (pop end-stack))
+ (dolist (push (ir2-block-pushed 2block))
+ (aver (not (memq push end-stack)))
+ (push push end-stack))
+ (aver (subsetp end end-stack))
+ (when (and tailp-lvar
+ (eq (ir2-lvar-kind (lvar-info tailp-lvar)) :unknown))
+ (aver (eq tailp-lvar (first end-stack)))
+ (pop end-stack))
+ (setf (ir2-block-end-stack 2block) end-stack))))
+
+(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 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
-;;; continuation at the end of BLOCK1 is different from that at the
-;;; start of BLOCK2 (its successor).
+;;; lvar at the end of BLOCK1 is different from that at the start of
+;;; BLOCK2 (its successor).
;;;
;;; We insert a call to a funny function in a new cleanup block
;;; introduced between BLOCK1 and BLOCK2. Since control analysis and
;;; LTN have already run, we must do make an IR2 block, then do
-;;; ADD-TO-EMIT-ORDER and LTN-ANALYZE-BELATED-BLOCK on the new block.
-;;; The new block is inserted after BLOCK1 in the emit order.
+;;; ADD-TO-EMIT-ORDER and LTN-ANALYZE-BELATED-BLOCK on the new
+;;; block. The new block is inserted after BLOCK1 in the emit order.
;;;
;;; If the control transfer between BLOCK1 and BLOCK2 represents a
-;;; tail-recursive return (:DELETED IR2-continuation) or a non-local
-;;; exit, then the cleanup code will never actually be executed. It
-;;; doesn't seem to be worth the risk of trying to optimize this,
-;;; since this rarely happens and wastes only space.
+;;; tail-recursive return or a non-local exit, then the cleanup code
+;;; will never actually be executed. It doesn't seem to be worth the
+;;; risk of trying to optimize this, since this rarely happens and
+;;; 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)))
- (last-popped (elt block1-stack
- (- (length block1-stack)
- (length block2-stack)
- 1))))
- (aver (tailp block2-stack block1-stack))
-
- (let* ((block (insert-cleanup-code block1 block2
- (continuation-next (block-start block2))
- `(%pop-values ',last-popped)))
- (2block (make-ir2-block block)))
- (setf (block-info block) 2block)
- (add-to-emit-order 2block (block-info block1))
- (ltn-analyze-belated-block block)))
+ (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)
+ `(progn ,@(cleanup-code))))
+ (2block (make-ir2-block block)))
+ (setf (block-info block) 2block)
+ (add-to-emit-order 2block (block-info block1))
+ (ltn-analyze-belated-block block))))
(values))
\f
;;;; 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))
+;;; Return a list of all the blocks containing genuine uses of one of
+;;; 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 continuations 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 continuations used across block boundaries.
-;;;
-;;; Do the backward graph walk, starting at each values receiver. We ignore
-;;; receivers that already have a non-null Start-Stack. These are nested
-;;; values receivers that have already been reached on another walk. We don't
-;;; want to clobber that result with our null initial stack.
+;;; 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-continuations block))
+ (find-pushed-lvars block))
- (dolist (block receivers)
- (unless (ir2-block-start-stack (block-info block))
- (stack-simulation-walk block ())))
+ ;;; 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)
+ (setq did-something t)))
+ while did-something)
- (dolist (block generators)
- (annotate-dead-values block))
+ (order-uvl-sets component)
(do-blocks (block component)
- (let ((top (car (ir2-block-end-stack (block-info block)))))
- (dolist (succ (block-succ block))
- (when (and (block-start succ)
- (not (eq (car (ir2-block-start-stack (block-info succ)))
- top)))
- (discard-unused-values block succ))))))
+ (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))))))
(values))