1 ;;;; This file implements the stack analysis phase in the compiler. We
2 ;;;; analyse lifetime of dynamically allocated object packets on stack
3 ;;;; and insert cleanups where necessary.
5 ;;;; Currently there are two kinds of interesting stack packets: UVLs,
6 ;;;; whose use and destination lie in different blocks, and LVARs of
7 ;;;; constructors of dynamic-extent objects.
9 ;;;; This software is part of the SBCL system. See the README file for
10 ;;;; more information.
12 ;;;; This software is derived from the CMU CL system, which was
13 ;;;; written at Carnegie Mellon University and released into the
14 ;;;; public domain. The software is in the public domain and is
15 ;;;; provided with absolutely no warranty. See the COPYING and CREDITS
16 ;;;; files for more information.
20 ;;; Scan through BLOCK looking for uses of :UNKNOWN lvars that have
21 ;;; their DEST outside of the block. We do some checking to verify the
22 ;;; invariant that all pushes come after the last pop.
23 (defun find-pushed-lvars (block)
24 (let* ((2block (block-info block))
25 (popped (ir2-block-popped 2block))
27 (lvar-dest (car (last popped)))
31 (do-nodes (node lvar block)
32 (when (eq node last-pop)
36 (or (lvar-dynamic-extent lvar)
37 (let ((dest (lvar-dest lvar))
38 (2lvar (lvar-info lvar)))
39 (and (not (eq (node-block dest) block))
41 (eq (ir2-lvar-kind 2lvar) :unknown)))))
42 (aver (or saw-last (not last-pop)))
45 (setf (ir2-block-pushed 2block) (pushed))))
48 ;;;; Computation of live UVL sets
49 (defun nle-block-nlx-info (block)
50 (let* ((start-node (block-start-node block))
51 (nlx-ref (ctran-next (node-next start-node)))
52 (nlx-info (constant-value (ref-leaf nlx-ref))))
54 (defun nle-block-entry-block (block)
55 (let* ((nlx-info (nle-block-nlx-info block))
56 (mess-up (cleanup-mess-up (nlx-info-cleanup nlx-info)))
57 (entry-block (node-block mess-up)))
60 ;;; Add LVARs from LATE to EARLY; use EQ to check whether EARLY has
62 (defun merge-uvl-live-sets (early late)
63 (declare (type list early late))
64 (dolist (e late early)
67 ;;; Update information on stacks of unknown-values LVARs on the
68 ;;; boundaries of BLOCK. Return true if the start stack has been
71 ;;; An LVAR is live at the end iff it is live at some of blocks, which
72 ;;; BLOCK can transfer control to. There are two kind of control
73 ;;; transfers: normal, expressed with BLOCK-SUCC, and NLX.
74 (defun update-uvl-live-sets (block)
75 (declare (type cblock block))
76 (let* ((2block (block-info block))
77 (original-start (ir2-block-start-stack 2block))
78 (end (ir2-block-end-stack 2block))
80 (dolist (succ (block-succ block))
81 (setq new-end (merge-uvl-live-sets new-end
82 (ir2-block-start-stack (block-info succ)))))
83 (map-block-nlxes (lambda (nlx-info)
84 (let* ((nle (nlx-info-target nlx-info))
85 (nle-start-stack (ir2-block-start-stack
87 (exit-lvar (nlx-info-lvar nlx-info))
88 (next-stack (if exit-lvar
89 (remove exit-lvar nle-start-stack)
91 (setq new-end (merge-uvl-live-sets
92 new-end next-stack))))
95 (dolist (lvar (cleanup-info dx-cleanup))
96 (let* ((generator (lvar-use lvar))
97 (block (node-block generator))
98 (2block (block-info block)))
99 (aver (eq generator (block-last block)))
100 ;; DX objects, living in the LVAR, are
101 ;; alive in the environment, protected by
102 ;; the CLEANUP. We also cannot move them
103 ;; (because, in general, we cannot track
104 ;; all references to them). Therefore,
105 ;; everything, allocated deeper than a DX
106 ;; object, should be kept alive until the
107 ;; object is deallocated.
108 (setq new-end (merge-uvl-live-sets
109 new-end (ir2-block-end-stack 2block)))
110 (setq new-end (merge-uvl-live-sets
111 new-end (ir2-block-pushed 2block)))))))
113 (setf (ir2-block-end-stack 2block) new-end)
115 (let ((start new-end))
116 (setq start (set-difference start (ir2-block-pushed 2block)))
117 (setq start (merge-uvl-live-sets start (ir2-block-popped 2block)))
119 ;; We cannot delete unused UVLs during NLX, so all UVLs live at
120 ;; ENTRY will be actually live at NLE.
122 ;; BUT, UNWIND-PROTECTor is called in the environment, which has
123 ;; nothing in common with the environment of its entry. So we
124 ;; fictively compute its stack from the containing cleanups, but
125 ;; do not propagate additional LVARs from the entry, thus
126 ;; preveting bogus stack cleanings.
128 ;; TODO: Insert a check that no values are discarded in UWP. Or,
129 ;; maybe, we just don't need to create NLX-ENTRY for UWP?
130 (when (and (eq (component-head (block-component block))
131 (first (block-pred block)))
132 (not (bind-p (block-start-node block))))
133 (let* ((nlx-info (nle-block-nlx-info block))
134 (cleanup (nlx-info-cleanup nlx-info)))
135 (unless (eq (cleanup-kind cleanup) :unwind-protect)
136 (let* ((entry-block (node-block (cleanup-mess-up cleanup)))
137 (entry-stack (ir2-block-start-stack (block-info entry-block))))
138 (setq start (merge-uvl-live-sets start entry-stack))))))
140 (when *check-consistency*
141 (aver (subsetp original-start start)))
142 (cond ((subsetp start original-start)
145 (setf (ir2-block-start-stack 2block) start)
149 ;;;; Ordering of live UVL stacks
151 ;;; Put UVLs on the start/end stacks of BLOCK in the right order. PRED
152 ;;; is a predecessor of BLOCK with already sorted stacks; because all
153 ;;; UVLs being live at the BLOCK start are live in PRED, we just need
154 ;;; to delete dead UVLs.
155 (defun order-block-uvl-sets (block pred)
156 (let* ((2block (block-info block))
157 (pred-end-stack (ir2-block-end-stack (block-info pred)))
158 (start (ir2-block-start-stack 2block))
159 (start-stack (loop for lvar in pred-end-stack
160 when (memq lvar start)
162 (end (ir2-block-end-stack 2block)))
163 (when *check-consistency*
164 (aver (subsetp start start-stack)))
165 (setf (ir2-block-start-stack 2block) start-stack)
167 (let* ((last (block-last block))
168 (tailp-lvar (if (node-tail-p last) (node-lvar last)))
169 (end-stack start-stack))
170 (dolist (pop (ir2-block-popped 2block))
171 (aver (eq pop (car end-stack)))
173 (dolist (push (ir2-block-pushed 2block))
174 (aver (not (memq push end-stack)))
175 (push push end-stack))
176 (aver (subsetp end end-stack))
177 (when (and tailp-lvar
178 (eq (ir2-lvar-kind (lvar-info tailp-lvar)) :unknown))
179 (aver (eq tailp-lvar (first end-stack)))
181 (setf (ir2-block-end-stack 2block) end-stack))))
183 (defun order-uvl-sets (component)
184 (clear-flags component)
185 (loop with head = (component-head component)
188 (do-blocks (block component)
189 (unless (block-flag block)
190 (let ((pred (find-if #'block-flag (block-pred block))))
191 (when (and (eq pred head)
192 (not (bind-p (block-start-node block))))
193 (let ((entry (nle-block-entry-block block)))
194 (setq pred (if (block-flag entry) entry nil))))
196 (setf (block-flag block) t)
197 (order-block-uvl-sets block pred))
199 (setq repeat-p t))))))
202 ;;; This is called when we discover that the stack-top unknown-values
203 ;;; lvar at the end of BLOCK1 is different from that at the start of
204 ;;; BLOCK2 (its successor).
206 ;;; We insert a call to a funny function in a new cleanup block
207 ;;; introduced between BLOCK1 and BLOCK2. Since control analysis and
208 ;;; LTN have already run, we must do make an IR2 block, then do
209 ;;; ADD-TO-EMIT-ORDER and LTN-ANALYZE-BELATED-BLOCK on the new
210 ;;; block. The new block is inserted after BLOCK1 in the emit order.
212 ;;; If the control transfer between BLOCK1 and BLOCK2 represents a
213 ;;; tail-recursive return or a non-local exit, then the cleanup code
214 ;;; will never actually be executed. It doesn't seem to be worth the
215 ;;; risk of trying to optimize this, since this rarely happens and
216 ;;; wastes only space.
217 (defun discard-unused-values (block1 block2)
218 (declare (type cblock block1 block2))
219 (collect ((cleanup-code))
220 (labels ((find-popped (before after)
221 ;; Returns (VALUES popped last-popped rest), where
222 ;; BEFORE = (APPEND popped rest) and
223 ;; (EQ (FIRST rest) (FIRST after))
225 (values before (first (last before)) nil)
226 (loop with first-preserved = (car after)
227 for last-popped = nil then maybe-popped
229 for maybe-popped = (car rest)
230 while (neq maybe-popped first-preserved)
231 collect maybe-popped into popped
232 finally (return (values popped last-popped rest)))))
233 (discard (before-stack after-stack)
235 ((eq (car before-stack) (car after-stack))
236 (binding* ((moved-count (mismatch before-stack after-stack)
239 (loop for moved-lvar in before-stack
241 collect moved-lvar into moved
242 collect `',moved-lvar into qmoved
243 finally (return (values moved qmoved))))
244 (q-last-moved (car (last qmoved)))
245 ((nil last-nipped rest)
246 (find-popped (nthcdr moved-count before-stack)
247 (nthcdr moved-count after-stack))))
249 `(%nip-values ',last-nipped ,q-last-moved
251 (discard (nconc moved rest) after-stack)))
253 (multiple-value-bind (popped last-popped rest)
254 (find-popped before-stack after-stack)
255 (declare (ignore popped))
256 (cleanup-code `(%pop-values ',last-popped))
257 (discard rest after-stack))))))
258 (discard (ir2-block-end-stack (block-info block1))
259 (ir2-block-start-stack (block-info block2))))
261 (let* ((block (insert-cleanup-code block1 block2
262 (block-start-node block2)
263 `(progn ,@(cleanup-code))))
264 (2block (make-ir2-block block)))
265 (setf (block-info block) 2block)
266 (add-to-emit-order 2block (block-info block1))
267 (ltn-analyze-belated-block block))))
273 ;;; Return a list of all the blocks containing genuine uses of one of
274 ;;; the RECEIVERS (blocks) and DX-LVARS. Exits are excluded, since
275 ;;; they don't drop through to the receiver.
276 (defun find-pushing-blocks (receivers dx-lvars)
277 (declare (list receivers dx-lvars))
278 (collect ((res nil adjoin))
279 (dolist (rec receivers)
280 (dolist (pop (ir2-block-popped (block-info rec)))
283 (res (node-block use))))))
284 (dolist (dx-lvar dx-lvars)
285 (do-uses (use dx-lvar)
286 (res (node-block use))))
289 ;;; Analyze the use of unknown-values and DX lvars in COMPONENT,
290 ;;; inserting cleanup code to discard values that are generated but
291 ;;; never received. This phase doesn't need to be run when
292 ;;; Values-Receivers and Dx-Lvars are null, i.e. there are no
293 ;;; unknown-values lvars used across block boundaries and no DX LVARs.
294 (defun stack-analyze (component)
295 (declare (type component component))
296 (let* ((2comp (component-info component))
297 (receivers (ir2-component-values-receivers 2comp))
298 (generators (find-pushing-blocks receivers
299 (component-dx-lvars component))))
301 (dolist (block generators)
302 (find-pushed-lvars block))
304 ;;; Compute sets of live UVLs and DX LVARs
305 (loop for did-something = nil
306 do (do-blocks-backwards (block component)
307 (when (update-uvl-live-sets block)
308 (setq did-something t)))
311 (order-uvl-sets component)
313 (do-blocks (block component)
314 (let ((top (ir2-block-end-stack (block-info block))))
315 (dolist (succ (block-succ block))
316 (when (and (block-start succ)
317 (not (eq (ir2-block-start-stack (block-info succ))
319 (discard-unused-values block succ))))))