X-Git-Url: http://repo.macrolet.net/gitweb/?a=blobdiff_plain;f=src%2Fcompiler%2Fstack.lisp;h=fccf4f8a8db902d340cf0acfa4b94b0cb097d5ce;hb=8902b8b6bd2e9285749dd39d313b33b6c69c5213;hp=f04e92cf8f8de96830056ecdc897826e98e936b8;hpb=5ec8d0c1c8b7939818b75118b472fac1af554f9a;p=sbcl.git diff --git a/src/compiler/stack.lisp b/src/compiler/stack.lisp index f04e92c..fccf4f8 100644 --- a/src/compiler/stack.lisp +++ b/src/compiler/stack.lisp @@ -1,7 +1,10 @@ ;;;; 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. @@ -14,218 +17,304 @@ (in-package "SB!C") -;;; 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))) + (lvar-dest (car (last popped))) nil))) (collect ((pushed)) (let ((saw-last nil)) - (do-nodes (node cont block) + (do-nodes (node lvar 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))))) + (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)) -;;;; annotation graph walk +;;;; 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)) -;;; 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 - (physenv-nlx-info (block-physenv 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)))))))) - - (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)) + (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.) +;;; Update information on stacks of unknown-values LVARs on the +;;; boundaries of BLOCK. Return true if the start stack has been +;;; changed. ;;; -;;; 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. -;;; -;;; 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)) + (let* ((generator (lvar-use lvar)) + (block (node-block generator)) + (2block (block-info block))) + (aver (eq generator (block-last 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, should be kept alive until the + ;; object is deallocated. + (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)) + +;;;; 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) + (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)) ;;; 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)) ;;;; 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)))))) + (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))) + (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))))) + (let ((top (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))) + (not (eq (ir2-block-start-stack (block-info succ)) top))) (discard-unused-values block succ))))))