| blob | 6a89ee3ba3d78733f34778cad72470edabf1bfe1 |
1 ;;;; This file contains the lifetime analysis phase in the compiler.
3 ;;;; This software is part of the SBCL system. See the README file for
4 ;;;; more information.
5 ;;;;
6 ;;;; This software is derived from the CMU CL system, which was
7 ;;;; written at Carnegie Mellon University and released into the
8 ;;;; public domain. The software is in the public domain and is
9 ;;;; provided with absolutely no warranty. See the COPYING and CREDITS
10 ;;;; files for more information.
13 \f
14 ;;;; utilities
16 ;;; Link in a GLOBAL-CONFLICTS structure for TN in BLOCK with NUMBER
17 ;;; as the LTN number. The conflict is inserted in the per-TN
18 ;;; GLOBAL-CONFLICTS thread after the TN's CURRENT-CONFLICT. We change
19 ;;; the CURRENT-CONFLICT to point to the new conflict. Since we scan
20 ;;; the blocks in reverse DFO, this list is automatically built in
21 ;;; order. We have to actually scan the current GLOBAL-TNs for the
22 ;;; block in order to keep that thread sorted.
32 new)
35 new)))
41 ;;; Do the actual insertion of the conflict NEW into BLOCK's global
42 ;;; conflicts.
56 ;;; Reset the CURRENT-CONFLICT slot in all packed TNs to point to the
57 ;;; head of the GLOBAL-CONFLICTS thread.
62 ;;; Cache the results of BLOCK-PHYSENV during lifetime analysis.
63 ;;;
64 ;;; Fetching the home-lambda of a block (needed in block-physenv) can
65 ;;; be an expensive operation under some circumstances, and it needs
66 ;;; to be done a lot during lifetime analysis when compiling with high
67 ;;; DEBUG (e.g. 30% of the total compilation time for CL-PPCRE with
68 ;;; DEBUG 3 just for that).
74 physenv)))
75 \f
76 ;;;; pre-pass
78 ;;; Convert TN (currently local) to be a global TN, since we
79 ;;; discovered that it is referenced in more than one block. We just
80 ;;; add a global-conflicts structure with a kind derived from the KILL
81 ;;; and LIVE sets.
88 :read-only
90 :write
92 tn block num))
95 ;;; Scan all references to packed TNs in block. We assign LTN numbers
96 ;;; to each referenced TN, and also build the Kill and Live sets that
97 ;;; summarize the references to each TN for purposes of lifetime
98 ;;; analysis.
99 ;;;
100 ;;; It is possible that we will run out of LTN numbers. If this
101 ;;; happens, then we return the VOP that we were processing at the
102 ;;; time we ran out, otherwise we return NIL.
103 ;;;
104 ;;; If a TN is referenced in more than one block, then we must
105 ;;; represent references using GLOBAL-CONFLICTS structures. When we
106 ;;; first see a TN, we assume it will be local. If we see a reference
107 ;;; later on in a different block, then we go back and fix the TN to
108 ;;; global.
109 ;;;
110 ;;; We must globalize TNs that have a block other than the current one
111 ;;; in their LOCAL slot and have no GLOBAL-CONFLICTS. The latter
112 ;;; condition is necessary because we always set Local and
113 ;;; LOCAL-NUMBER when we process a reference to a TN, even when the TN
114 ;;; is already known to be global.
115 ;;;
116 ;;; When we see reference to global TNs during the scan, we add the
117 ;;; global-conflict as :READ-ONLY, since we don't know the correct
118 ;;; kind until we are done scanning the block.
153 nil)
155 ;;; Finish up the global conflicts for TNs referenced in BLOCK
156 ;;; according to the local Kill and Live sets.
157 ;;;
158 ;;; We set the kind for TNs already in the global-TNs. If not written
159 ;;; at all, then is :READ-ONLY, the default. Must have been referenced
160 ;;; somehow, or we wouldn't have conflicts for it.
161 ;;;
162 ;;; We also iterate over all the local TNs, looking for TNs local to
163 ;;; this block that are still live at the block beginning, and thus
164 ;;; must be global. This case is only important when a TN is read in a
165 ;;; block but not written in any other, since otherwise the write
166 ;;; would promote the TN to global. But this does happen with various
167 ;;; passing-location TNs that are magically written. This also serves
168 ;;; to propagate the lives of erroneously uninitialized TNs so that
169 ;;; consistency checks can detect them.
181 :write
196 ;;; Move the code after the VOP LOSE in 2BLOCK into its own block. The
197 ;;; block is linked into the emit order following 2BLOCK. NUMBER is
198 ;;; the block number assigned to the new block. We return the new
199 ;;; block.
219 new))
221 ;;; Clear the global and local conflict info in BLOCK so that we can
222 ;;; recompute it without any old cruft being retained. It is assumed
223 ;;; that all LTN numbers are in use.
224 ;;;
225 ;;; First we delete all the global conflicts. The conflict we are
226 ;;; deleting must be the last in the TN's GLOBAL-CONFLICTS, but we
227 ;;; must scan for it in order to find the previous conflict.
228 ;;;
229 ;;; Next, we scan the local TNs, nulling out the LOCAL slot in all TNs
230 ;;; with no global conflicts. This allows these TNs to be treated as
231 ;;; local when we scan the block again.
232 ;;;
233 ;;; If there are conflicts, then we set LOCAL to one of the
234 ;;; conflicting blocks. This ensures that LOCAL doesn't hold over
235 ;;; BLOCK as its value, causing the subsequent reanalysis to think
236 ;;; that the TN has already been seen in that block.
237 ;;;
238 ;;; This function must not be called on blocks that have :MORE TNs.
268 nil))))))
272 ;;; This provides a panic mode for assigning LTN numbers when there is
273 ;;; a VOP with so many more operands that they can't all be assigned
274 ;;; distinct numbers. When this happens, we recover by assigning all
275 ;;; the &MORE operands the same LTN number. We can get away with this,
276 ;;; since all &MORE args (and results) are referenced simultaneously
277 ;;; as far as conflict analysis is concerned.
278 ;;;
279 ;;; BLOCK is the IR2-BLOCK that the MORE VOP is at the end of. OPS is
280 ;;; the full argument or result TN-REF list. Fixed is the types of the
281 ;;; fixed operands (used only to skip those operands.)
282 ;;;
283 ;;; What we do is grab a LTN number, then make a :READ-ONLY global
284 ;;; conflict for each more operand TN. We require that there be no
285 ;;; existing global conflict in BLOCK for any of the operands. Since
286 ;;; conflicts must be cleared before the first call, this only
287 ;;; prohibits the same TN being used both as a more operand and as any
288 ;;; other operand to the same VOP.
289 ;;;
290 ;;; We don't have to worry about getting the correct conflict kind,
291 ;;; since INIT-GLOBAL-CONFLICT-KIND will fix things up. Similarly,
292 ;;; FIND-LOCAL-REFERENCES will set the local conflict bit
293 ;;; corresponding to this call.
294 ;;;
295 ;;; We also set the LOCAL and LOCAL-NUMBER slots in each TN. It is
296 ;;; possible that there are no operands in any given call to this
297 ;;; function, but there had better be either some more args or more
298 ;;; results.
334 ;;; Loop over the blocks in COMPONENT, assigning LTN numbers and
335 ;;; recording TN birth and death. The only interesting action is when
336 ;;; we run out of local TN numbers while finding local references.
337 ;;;
338 ;;; If we run out of LTN numbers while processing a VOP within the
339 ;;; block, then we just split off the VOPs we have successfully
340 ;;; processed into their own block.
341 ;;;
342 ;;; If we run out of LTN numbers while processing the our first VOP
343 ;;; (the last in the block), then it must be the case that this VOP
344 ;;; has large more operands. We split the VOP into its own block, and
345 ;;; then call COALESCE-MORE-LTN-NUMBERS to assign all the more
346 ;;; args/results the same LTN number(s).
347 ;;;
348 ;;; In either case, we clear the lifetime information that we computed
349 ;;; so far, recomputing it after taking corrective action.
350 ;;;
351 ;;; Whenever we split a block, we finish the pre-pass on the split-off
352 ;;; block by doing FIND-LOCAL-REFERENCES and
353 ;;; INIT-GLOBAL-CONFLICT-KIND. This can't run out of LTN numbers.
394 \f
395 ;;;; environment TN stuff
397 ;;; Add a :LIVE global conflict for TN in 2BLOCK if there is none
398 ;;; present. If DEBUG-P is false (a :ENVIRONMENT TN), then modify any
399 ;;; existing conflict to be :LIVE.
415 nil)
421 ;;; Iterate over all the blocks in ENV, setting up :LIVE conflicts for
422 ;;; TN. We make the TN global if it isn't already. The TN must have at
423 ;;; least one reference.
437 prev))))
443 ;;; Iterate over all the environment TNs, adding always-live conflicts
444 ;;; as appropriate.
456 ;;; Convert a :NORMAL or :DEBUG-ENVIRONMENT TN to an :ENVIRONMENT TN.
457 ;;; This requires adding :LIVE conflicts to all blocks in TN-PHYSENV.
462 (:debug-environment
467 (:normal
475 \f
476 ;;;; flow analysis
478 ;;; For each GLOBAL-TN in BLOCK2 that is :LIVE, :READ or :READ-ONLY,
479 ;;; ensure that there is a corresponding GLOBAL-CONFLICT in BLOCK1. If
480 ;;; there is none, make a :LIVE GLOBAL-CONFLICT. If there is a
481 ;;; :READ-ONLY conflict, promote it to :LIVE.
482 ;;;
483 ;;; If we did add a new conflict, return true, otherwise false. We
484 ;;; don't need to return true when we promote a :READ-ONLY conflict,
485 ;;; since it doesn't reveal any new information to predecessors of
486 ;;; BLOCK1.
487 ;;;
488 ;;; We use the TN-CURRENT-CONFLICT to walk through the global
489 ;;; conflicts. Since the global conflicts for a TN are ordered by
490 ;;; block, we can be sure that the CURRENT-CONFLICT always points at
491 ;;; or before the block that we are looking at. This allows us to
492 ;;; quickly determine if there is a global conflict for a given TN in
493 ;;; BLOCK1.
494 ;;;
495 ;;; When we scan down the conflicts, we know that there must be at
496 ;;; least one conflict for TN, since we got our hands on TN by picking
497 ;;; it out of a conflict in BLOCK2.
498 ;;;
499 ;;; We leave the CURRENT-CONFLICT pointing to the conflict for BLOCK1.
500 ;;; The CURRENT-CONFLICT must be initialized to the head of the
501 ;;; GLOBAL-CONFLICTS for the TN between each flow analysis iteration.
519 number1))
526 (:read-only
530 nil)
537 did-something))
539 ;;; Do backward global flow analysis to find all TNs live at each
540 ;;; block boundary.
550 prev))))
566 \f
567 ;;;; post-pass
569 ;;; Note that TN conflicts with all current live TNs. NUM is TN's LTN
570 ;;; number. We bit-ior LIVE-BITS with TN's LOCAL-CONFLICTS, and set TN's
571 ;;; number in the conflicts of all TNs in LIVE-LIST.
583 ;;; Compute a bit vector of the TNs live after VOP that aren't results.
594 live))
596 ;;; This is used to determine whether a :DEBUG-ENVIRONMENT TN should
597 ;;; be considered live at block end. We return true if a VOP with
598 ;;; non-null SAVE-P appears before the first read of TN (hence is seen
599 ;;; first in our backward scan.)
607 ;;; If the block has no successors, or its successor is the component
608 ;;; tail, then all :DEBUG-ENVIRONMENT TNs are always added, regardless
609 ;;; of whether they appeared to be live. This ensures that these TNs
610 ;;; are considered to be live throughout blocks that read them, but
611 ;;; don't have any interesting successors (such as a return or tail
612 ;;; call.) In this case, we set the corresponding bit in LIVE-IN as
613 ;;; well.
640 ;;; Return as values, a LTN bit-vector and a list (threaded by
641 ;;; TN-NEXT*) representing the TNs live at the end of BLOCK (exclusive
642 ;;; of :LIVE TNs).
643 ;;;
644 ;;; We iterate over the TNs in the global conflicts that are live at
645 ;;; the block end, setting up the TN-LOCAL-CONFLICTS and
646 ;;; TN-LOCAL-NUMBER, and adding the TN to the live list.
647 ;;;
648 ;;; If a :MORE result is not live, we effectively fake a read to it.
649 ;;; This is part of the action described in ENSURE-RESULTS-LIVE.
650 ;;;
651 ;;; At the end, we call MAKE-DEBUG-ENVIRONEMNT-TNS-LIVE to make debug
652 ;;; environment TNs appear live when appropriate, even when they
653 ;;; aren't.
654 ;;;
655 ;;; ### Note: we alias the global-conflicts-conflicts here as the
656 ;;; tn-local-conflicts.
688 ;;; A function called in CONFLICT-ANALYZE-1-BLOCK when we have a VOP
689 ;;; with SAVE-P true. We compute the save-set, and if :FORCE-TO-STACK,
690 ;;; force all the live TNs to be stack environment TNs.
702 tn
706 ;;; FIXME: The next 3 macros aren't needed in the target runtime.
707 ;;; Figure out some way to make them only at build time. (Just
708 ;;; (EVAL-WHEN (:COMPILE-TOPLEVEL :EXECUTE) (DEFMACRO ..)) isn't good enough,
709 ;;; since we need CL:DEFMACRO at build-the-cross-compiler time and
710 ;;; SB!XC:DEFMACRO at run-the-cross-compiler time.)
712 ;;; This is used in SCAN-VOP-REFS to simultaneously do something to
713 ;;; all of the TNs referenced by a big more arg. We have to treat
714 ;;; these TNs specially, since when we set or clear the bit in the
715 ;;; live TNs, the represents a change in the liveness of all the more
716 ;;; TNs. If we iterated as normal, the next more ref would be thought
717 ;;; to be not live when it was, etc. We update Ref to be the last
718 ;;; :more ref we scanned, so that the main loop will step to the next
719 ;;; non-more ref.
732 ;;; Handle the part of CONFLICT-ANALYZE-1-BLOCK that scans the REFs
733 ;;; for the current VOP. This macro shamelessly references free
734 ;;; variables in C-A-1-B.
755 ;;; This macro is called by CONFLICT-ANALYZE-1-BLOCK to scan the
756 ;;; current VOP's results, and make any dead ones live. This is
757 ;;; necessary, since even though a result is dead after the VOP, it
758 ;;; may be in use for an extended period within the VOP (especially if
759 ;;; it has :FROM specified.) During this interval, temporaries must be
760 ;;; noted to conflict with the result. More results are finessed in
761 ;;; COMPUTE-INITIAL-CONFLICTS, so we ignore them here.
773 ;;; Compute the block-local conflict information for BLOCK. We iterate
774 ;;; over all the TN-REFs in a block in reference order, maintaining
775 ;;; the set of live TNs in both a list and a bit-vector
776 ;;; representation.
790 ;;; Conflict analyze each block, and also add it.
795 \f
796 ;;;; alias TN stuff
798 ;;; Destructively modify OCONF to include the conflict information in CONF.
816 ;; Make original conflict with all the local TNs the alias
817 ;; conflicted with.
820 t)
824 ;; Make all the local TNs that conflicted with the alias
825 ;; conflict with the original.
831 ;; Same for global TNs...
837 ;; Make the original TN live everywhere that the alias was live.
846 ;; Delete the alias's conflict info.
851 conf))
855 ;;; Co-opt CONF to be a conflict for TN.
863 conf)
870 ;;; Do CONVERT-TO-GLOBAL on TN if it has no global conflicts. Copy the
871 ;;; local conflicts into the global bit vector.
879 t))
884 ;;; For each :ALIAS TN, destructively merge the conflict info into the
885 ;;; original TN and replace the uses of the alias.
886 ;;;
887 ;;; For any block that uses only the alias TN, just insert that
888 ;;; conflict into the conflicts for the original TN, changing the LTN
889 ;;; map to refer to the original TN. This gives a result
890 ;;; indistinguishable from the what there would have been if the
891 ;;; original TN had always been referenced. This leaves no sign that
892 ;;; an alias TN was ever involved.
893 ;;;
894 ;;; If a block has references to both the alias and the original TN,
895 ;;; then we call MERGE-ALIAS-BLOCK-CONFLICTS to combine the conflicts
896 ;;; into the original conflict.
929 conf
931 oconf))
952 ;;; On high debug levels, for all variables that a lambda closes over
953 ;;; convert the TNs to :ENVIRONMENT TNs (in the physical environment
954 ;;; of that lambda). This way the debugger can display the variables.
964 \f
972 \f
973 ;;;; conflict testing
975 ;;; Test for a conflict between the local TN X and the global TN Y. We
976 ;;; just look for a global conflict of Y in X's block, and then test
977 ;;; for conflict in that block.
978 ;;;
979 ;;; [### Might be more efficient to scan Y's global conflicts. This
980 ;;; depends on whether there are more global TNs than blocks.]
990 num))))))))))
992 ;;; Test for conflict between two global TNs X and Y.
1011 ;; x-conf, y-conf true, x-num, y-num corresponding block numbers.
1019 ltn-num-x)))
1024 ;;; Return true if X and Y are distinct and the lifetimes of X and Y
1025 ;;; overlap at any point.