| blob | 9d28fbdfc5b92a30eb97e24f27bb8d37a35f022b |
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 ;;; Return true if TN represents a closed-over variable with an
422 ;;; "implicit" value-cell.
429 ;;; If BLOCK ends with a TAIL LOCAL COMBINATION, the function called.
430 ;;; Otherwise, NIL.
438 ;;; Iterate over all the blocks in ENV, setting up :LIVE conflicts for
439 ;;; TN. We make the TN global if it isn't already. The TN must have at
440 ;;; least one reference.
444 ;; Prevent infinite recursion due to recursive tail calls.
457 prev))))
461 ;; If BLOCK ends with a TAIL LOCAL COMBINATION and TN is an
462 ;; "implicit value cell" then setup conflicts for the callee
463 ;; function as well.
471 ;;; Iterate over all the environment TNs, adding always-live conflicts
472 ;;; as appropriate.
484 ;;; Convert a :NORMAL or :DEBUG-ENVIRONMENT TN to an :ENVIRONMENT TN.
485 ;;; This requires adding :LIVE conflicts to all blocks in TN-PHYSENV.
490 (:debug-environment
495 (:normal
503 \f
504 ;;;; flow analysis
506 ;;; For each GLOBAL-TN in BLOCK2 that is :LIVE, :READ or :READ-ONLY,
507 ;;; ensure that there is a corresponding GLOBAL-CONFLICT in BLOCK1. If
508 ;;; there is none, make a :LIVE GLOBAL-CONFLICT. If there is a
509 ;;; :READ-ONLY conflict, promote it to :LIVE.
510 ;;;
511 ;;; If we did add a new conflict, return true, otherwise false. We
512 ;;; don't need to return true when we promote a :READ-ONLY conflict,
513 ;;; since it doesn't reveal any new information to predecessors of
514 ;;; BLOCK1.
515 ;;;
516 ;;; We use the TN-CURRENT-CONFLICT to walk through the global
517 ;;; conflicts. Since the global conflicts for a TN are ordered by
518 ;;; block, we can be sure that the CURRENT-CONFLICT always points at
519 ;;; or before the block that we are looking at. This allows us to
520 ;;; quickly determine if there is a global conflict for a given TN in
521 ;;; BLOCK1.
522 ;;;
523 ;;; When we scan down the conflicts, we know that there must be at
524 ;;; least one conflict for TN, since we got our hands on TN by picking
525 ;;; it out of a conflict in BLOCK2.
526 ;;;
527 ;;; We leave the CURRENT-CONFLICT pointing to the conflict for BLOCK1.
528 ;;; The CURRENT-CONFLICT must be initialized to the head of the
529 ;;; GLOBAL-CONFLICTS for the TN between each flow analysis iteration.
531 ;;; FASTP is a KLUDGE: SBCL used to update the current-conflict only
532 ;;; for the read-only case, but switched at one point to always
533 ;;; updating it. This generally speeds up the compiler nicely, but
534 ;;; sometimes it causes an infinite loop in the updating machinery,
535 ;;; We cheat by switching of the fast path if it seems we're looping
536 ;;; longer then expected.
554 number1))
561 (:read-only
565 nil)
575 did-something))
577 ;;; Do backward global flow analysis to find all TNs live at each
578 ;;; block boundary.
580 ;; KLUDGE: This is the second part of the FASTP kludge in
581 ;; propagate-live-tns: we pass fastp for ten first attempts,
582 ;; and then switch to the works-for-sure version.
583 ;;
584 ;; The upstream uses the fast version always, but sometimes
585 ;; that gets stuck in a loop...
587 do
595 prev))))
611 \f
612 ;;;; post-pass
614 ;;; Note that TN conflicts with all current live TNs. NUM is TN's LTN
615 ;;; number. We bit-ior LIVE-BITS with TN's LOCAL-CONFLICTS, and set TN's
616 ;;; number in the conflicts of all TNs in LIVE-LIST.
628 ;;; Compute a bit vector of the TNs live after VOP that aren't results.
639 live))
641 ;;; This is used to determine whether a :DEBUG-ENVIRONMENT TN should
642 ;;; be considered live at block end. We return true if a VOP with
643 ;;; non-null SAVE-P appears before the first read of TN (hence is seen
644 ;;; first in our backward scan.)
652 ;;; If the block has no successors, or its successor is the component
653 ;;; tail, then all :DEBUG-ENVIRONMENT TNs are always added, regardless
654 ;;; of whether they appeared to be live. This ensures that these TNs
655 ;;; are considered to be live throughout blocks that read them, but
656 ;;; don't have any interesting successors (such as a return or tail
657 ;;; call.) In this case, we set the corresponding bit in LIVE-IN as
658 ;;; well.
685 ;;; Return as values, a LTN bit-vector and a list (threaded by
686 ;;; TN-NEXT*) representing the TNs live at the end of BLOCK (exclusive
687 ;;; of :LIVE TNs).
688 ;;;
689 ;;; We iterate over the TNs in the global conflicts that are live at
690 ;;; the block end, setting up the TN-LOCAL-CONFLICTS and
691 ;;; TN-LOCAL-NUMBER, and adding the TN to the live list.
692 ;;;
693 ;;; If a :MORE result is not live, we effectively fake a read to it.
694 ;;; This is part of the action described in ENSURE-RESULTS-LIVE.
695 ;;;
696 ;;; At the end, we call MAKE-DEBUG-ENVIRONEMNT-TNS-LIVE to make debug
697 ;;; environment TNs appear live when appropriate, even when they
698 ;;; aren't.
699 ;;;
700 ;;; ### Note: we alias the global-conflicts-conflicts here as the
701 ;;; tn-local-conflicts.
733 ;;; A function called in CONFLICT-ANALYZE-1-BLOCK when we have a VOP
734 ;;; with SAVE-P true. We compute the save-set, and if :FORCE-TO-STACK,
735 ;;; force all the live TNs to be stack environment TNs.
747 tn
751 ;;; FIXME: The next 3 macros aren't needed in the target runtime.
752 ;;; Figure out some way to make them only at build time. (Just
753 ;;; (EVAL-WHEN (:COMPILE-TOPLEVEL :EXECUTE) (DEFMACRO ..)) isn't good enough,
754 ;;; since we need CL:DEFMACRO at build-the-cross-compiler time and
755 ;;; SB!XC:DEFMACRO at run-the-cross-compiler time.)
757 ;;; This is used in SCAN-VOP-REFS to simultaneously do something to
758 ;;; all of the TNs referenced by a big more arg. We have to treat
759 ;;; these TNs specially, since when we set or clear the bit in the
760 ;;; live TNs, the represents a change in the liveness of all the more
761 ;;; TNs. If we iterated as normal, the next more ref would be thought
762 ;;; to be not live when it was, etc. We update Ref to be the last
763 ;;; :more ref we scanned, so that the main loop will step to the next
764 ;;; non-more ref.
777 ;;; Handle the part of CONFLICT-ANALYZE-1-BLOCK that scans the REFs
778 ;;; for the current VOP. This macro shamelessly references free
779 ;;; variables in C-A-1-B.
800 ;;; This macro is called by CONFLICT-ANALYZE-1-BLOCK to scan the
801 ;;; current VOP's results, and make any dead ones live. This is
802 ;;; necessary, since even though a result is dead after the VOP, it
803 ;;; may be in use for an extended period within the VOP (especially if
804 ;;; it has :FROM specified.) During this interval, temporaries must be
805 ;;; noted to conflict with the result. More results are finessed in
806 ;;; COMPUTE-INITIAL-CONFLICTS, so we ignore them here.
818 ;;; Compute the block-local conflict information for BLOCK. We iterate
819 ;;; over all the TN-REFs in a block in reference order, maintaining
820 ;;; the set of live TNs in both a list and a bit-vector
821 ;;; representation.
835 ;;; Conflict analyze each block, and also add it.
840 \f
841 ;;;; alias TN stuff
843 ;;; Destructively modify OCONF to include the conflict information in CONF.
861 ;; Make original conflict with all the local TNs the alias
862 ;; conflicted with.
865 t)
869 ;; Make all the local TNs that conflicted with the alias
870 ;; conflict with the original.
876 ;; Same for global TNs...
882 ;; Make the original TN live everywhere that the alias was live.
891 ;; Delete the alias's conflict info.
896 conf))
900 ;;; Co-opt CONF to be a conflict for TN.
908 conf)
915 ;;; Do CONVERT-TO-GLOBAL on TN if it has no global conflicts. Copy the
916 ;;; local conflicts into the global bit vector.
924 t))
929 ;;; For each :ALIAS TN, destructively merge the conflict info into the
930 ;;; original TN and replace the uses of the alias.
931 ;;;
932 ;;; For any block that uses only the alias TN, just insert that
933 ;;; conflict into the conflicts for the original TN, changing the LTN
934 ;;; map to refer to the original TN. This gives a result
935 ;;; indistinguishable from the what there would have been if the
936 ;;; original TN had always been referenced. This leaves no sign that
937 ;;; an alias TN was ever involved.
938 ;;;
939 ;;; If a block has references to both the alias and the original TN,
940 ;;; then we call MERGE-ALIAS-BLOCK-CONFLICTS to combine the conflicts
941 ;;; into the original conflict.
974 conf
976 oconf))
997 ;;; On high debug levels, for all variables that a lambda closes over
998 ;;; convert the TNs to :ENVIRONMENT TNs (in the physical environment
999 ;;; of that lambda). This way the debugger can display the variables.
1009 \f
1017 \f
1018 ;;;; conflict testing
1020 ;;; Test for a conflict between the local TN X and the global TN Y. We
1021 ;;; just look for a global conflict of Y in X's block, and then test
1022 ;;; for conflict in that block.
1023 ;;;
1024 ;;; [### Might be more efficient to scan Y's global conflicts. This
1025 ;;; depends on whether there are more global TNs than blocks.]
1035 num))))))))))
1037 ;;; Test for conflict between two global TNs X and Y.
1056 ;; x-conf, y-conf true, x-num, y-num corresponding block numbers.
1064 ltn-num-x)))
1069 ;;; Return true if X and Y are distinct and the lifetimes of X and Y
1070 ;;; overlap at any point.