1 {-# OPTIONS -fno-warn-missing-signatures #-}
2 -----------------------------------------------------------------------------
4 -- The register allocator
6 -- (c) The University of Glasgow 2004
8 -----------------------------------------------------------------------------
11 The algorithm is roughly:
13 1) Compute strongly connected components of the basic block list.
15 2) Compute liveness (mapping from pseudo register to
18 3) Walk instructions in each basic block. We keep track of
19 (a) Free real registers (a bitmap?)
20 (b) Current assignment of temporaries to machine registers and/or
21 spill slots (call this the "assignment").
22 (c) Partial mapping from basic block ids to a virt-to-loc mapping.
23 When we first encounter a branch to a basic block,
24 we fill in its entry in this table with the current mapping.
27 (a) For each real register clobbered by this instruction:
28 If a temporary resides in it,
29 If the temporary is live after this instruction,
30 Move the temporary to another (non-clobbered & free) reg,
31 or spill it to memory. Mark the temporary as residing
32 in both memory and a register if it was spilled (it might
33 need to be read by this instruction).
34 (ToDo: this is wrong for jump instructions?)
36 (b) For each temporary *read* by the instruction:
37 If the temporary does not have a real register allocation:
38 - Allocate a real register from the free list. If
40 - Find a temporary to spill. Pick one that is
41 not used in this instruction (ToDo: not
43 - generate a spill instruction
44 - If the temporary was previously spilled,
45 generate an instruction to read the temp from its spill loc.
46 (optimisation: if we can see that a real register is going to
47 be used soon, then don't use it for allocation).
49 (c) Update the current assignment
51 (d) If the intstruction is a branch:
52 if the destination block already has a register assignment,
53 Generate a new block with fixup code and redirect the
54 jump to the new block.
56 Update the block id->assignment mapping with the current
59 (e) Delete all register assignments for temps which are read
60 (only) and die here. Update the free register list.
62 (f) Mark all registers clobbered by this instruction as not free,
63 and mark temporaries which have been spilled due to clobbering
64 as in memory (step (a) marks then as in both mem & reg).
66 (g) For each temporary *written* by this instruction:
67 Allocate a real register as for (b), spilling something
69 - except when updating the assignment, drop any memory
70 locations that the temporary was previously in, since
71 they will be no longer valid after this instruction.
73 (h) Delete all register assignments for temps which are
74 written and die here (there should rarely be any). Update
75 the free register list.
77 (i) Rewrite the instruction with the new mapping.
79 (j) For each spilled reg known to be now dead, re-add its stack slot
84 module RegAlloc.Linear.Main (
86 module RegAlloc.Linear.Base,
87 module RegAlloc.Linear.Stats
90 #include "HsVersions.h"
93 import RegAlloc.Linear.State
94 import RegAlloc.Linear.Base
95 import RegAlloc.Linear.StackMap
96 import RegAlloc.Linear.FreeRegs
97 import RegAlloc.Linear.Stats
98 import RegAlloc.Linear.JoinToTargets
100 import RegAlloc.Liveness
105 import Cmm hiding (RegSet)
118 #include "../includes/stg/MachRegs.h"
121 -- -----------------------------------------------------------------------------
122 -- Top level of the register allocator
124 -- Allocate registers
126 :: (Outputable instr, Instruction instr)
128 -> UniqSM (NatCmmTop instr, Maybe RegAllocStats)
130 regAlloc (CmmData sec d)
135 regAlloc (CmmProc (LiveInfo info _ _) lbl params [])
136 = return ( CmmProc info lbl params (ListGraph [])
139 regAlloc (CmmProc static lbl params sccs)
140 | LiveInfo info (Just first_id) (Just block_live) <- static
142 -- do register allocation on each component.
143 (final_blocks, stats)
144 <- linearRegAlloc first_id block_live sccs
146 -- make sure the block that was first in the input list
147 -- stays at the front of the output
148 let ((first':_), rest')
149 = partition ((== first_id) . blockId) final_blocks
151 return ( CmmProc info lbl params (ListGraph (first' : rest'))
154 -- bogus. to make non-exhaustive match warning go away.
155 regAlloc (CmmProc _ _ _ _)
156 = panic "RegAllocLinear.regAlloc: no match"
159 -- -----------------------------------------------------------------------------
160 -- Linear sweep to allocate registers
163 -- | Do register allocation on some basic blocks.
164 -- But be careful to allocate a block in an SCC only if it has
165 -- an entry in the block map or it is the first block.
168 :: (Outputable instr, Instruction instr)
169 => BlockId -- ^ the first block
170 -> BlockMap RegSet -- ^ live regs on entry to each basic block
171 -> [SCC (LiveBasicBlock instr)] -- ^ instructions annotated with "deaths"
172 -> UniqSM ([NatBasicBlock instr], RegAllocStats)
174 linearRegAlloc first_id block_live sccs
176 let (_, _, stats, blocks) =
177 runR emptyBlockMap initFreeRegs emptyRegMap emptyStackMap us
178 $ linearRA_SCCs first_id block_live [] sccs
180 return (blocks, stats)
182 linearRA_SCCs _ _ blocksAcc []
183 = return $ reverse blocksAcc
185 linearRA_SCCs first_id block_live blocksAcc (AcyclicSCC block : sccs)
186 = do blocks' <- processBlock block_live block
187 linearRA_SCCs first_id block_live
188 ((reverse blocks') ++ blocksAcc)
191 linearRA_SCCs first_id block_live blocksAcc (CyclicSCC blocks : sccs)
193 blockss' <- process first_id block_live blocks [] (return [])
194 linearRA_SCCs first_id block_live
195 (reverse (concat blockss') ++ blocksAcc)
198 {- from John Dias's patch 2008/10/16:
199 The linear-scan allocator sometimes allocates a block
200 before allocating one of its predecessors, which could lead to
201 inconsistent allocations. Make it so a block is only allocated
202 if a predecessor has set the "incoming" assignments for the block, or
203 if it's the procedure's entry block.
205 BL 2009/02: Careful. If the assignment for a block doesn't get set for
206 some reason then this function will loop. We should probably do some
207 more sanity checking to guard against this eventuality.
210 process _ _ [] [] accum
211 = return $ reverse accum
213 process first_id block_live [] next_round accum
214 = process first_id block_live next_round [] accum
216 process first_id block_live (b@(BasicBlock id _) : blocks) next_round accum
218 block_assig <- getBlockAssigR
220 if isJust (lookupBlockEnv block_assig id)
223 b' <- processBlock block_live b
224 process first_id block_live blocks next_round (b' : accum)
226 else process first_id block_live blocks (b : next_round) accum
229 -- | Do register allocation on this basic block
232 :: (Outputable instr, Instruction instr)
233 => BlockMap RegSet -- ^ live regs on entry to each basic block
234 -> LiveBasicBlock instr -- ^ block to do register allocation on
235 -> RegM [NatBasicBlock instr] -- ^ block with registers allocated
237 processBlock block_live (BasicBlock id instrs)
240 <- linearRA block_live [] [] id instrs
241 return $ BasicBlock id instrs' : fixups
244 -- | Load the freeregs and current reg assignment into the RegM state
245 -- for the basic block with this BlockId.
246 initBlock :: BlockId -> RegM ()
248 = do block_assig <- getBlockAssigR
249 case lookupBlockEnv block_assig id of
250 -- no prior info about this block: assume everything is
251 -- free and the assignment is empty.
253 -> do -- pprTrace "initFreeRegs" (text $ show initFreeRegs) (return ())
255 setFreeRegsR initFreeRegs
256 setAssigR emptyRegMap
258 -- load info about register assignments leading into this block.
259 Just (freeregs, assig)
260 -> do setFreeRegsR freeregs
264 -- | Do allocation for a sequence of instructions.
266 :: (Outputable instr, Instruction instr)
267 => BlockMap RegSet -- ^ map of what vregs are live on entry to each block.
268 -> [instr] -- ^ accumulator for instructions already processed.
269 -> [NatBasicBlock instr] -- ^ accumulator for blocks of fixup code.
270 -> BlockId -- ^ id of the current block, for debugging.
271 -> [LiveInstr instr] -- ^ liveness annotated instructions in this block.
273 -> RegM ( [instr] -- instructions after register allocation
274 , [NatBasicBlock instr]) -- fresh blocks of fixup code.
277 linearRA _ accInstr accFixup _ []
279 ( reverse accInstr -- instrs need to be returned in the correct order.
280 , accFixup) -- it doesn't matter what order the fixup blocks are returned in.
283 linearRA block_live accInstr accFixups id (instr:instrs)
285 (accInstr', new_fixups)
286 <- raInsn block_live accInstr id instr
288 linearRA block_live accInstr' (new_fixups ++ accFixups) id instrs
291 -- | Do allocation for a single instruction.
293 :: (Outputable instr, Instruction instr)
294 => BlockMap RegSet -- ^ map of what vregs are love on entry to each block.
295 -> [instr] -- ^ accumulator for instructions already processed.
296 -> BlockId -- ^ the id of the current block, for debugging
297 -> LiveInstr instr -- ^ the instr to have its regs allocated, with liveness info.
299 ( [instr] -- new instructions
300 , [NatBasicBlock instr]) -- extra fixup blocks
302 raInsn _ new_instrs _ (Instr ii Nothing)
303 | Just n <- takeDeltaInstr ii
305 return (new_instrs, [])
307 raInsn _ new_instrs _ (Instr ii Nothing)
309 = return (new_instrs, [])
312 raInsn block_live new_instrs id (Instr instr (Just live))
316 -- If we have a reg->reg move between virtual registers, where the
317 -- src register is not live after this instruction, and the dst
318 -- register does not already have an assignment,
319 -- and the source register is assigned to a register, not to a spill slot,
320 -- then we can eliminate the instruction.
321 -- (we can't eliminitate it if the source register is on the stack, because
322 -- we do not want to use one spill slot for different virtual registers)
323 case takeRegRegMoveInstr instr of
324 Just (src,dst) | src `elementOfUniqSet` (liveDieRead live),
326 not (dst `elemUFM` assig),
327 Just (InReg _) <- (lookupUFM assig src) -> do
329 (RegReal rr) -> setAssigR (addToUFM assig dst (InReg rr))
330 -- if src is a fixed reg, then we just map dest to this
331 -- reg in the assignment. src must be an allocatable reg,
332 -- otherwise it wouldn't be in r_dying.
333 _virt -> case lookupUFM assig src of
334 Nothing -> panic "raInsn"
336 setAssigR (addToUFM (delFromUFM assig src) dst loc)
338 -- we have eliminated this instruction
340 freeregs <- getFreeRegsR
342 pprTrace "raInsn" (text "ELIMINATED: " <> docToSDoc (pprInstr instr)
343 $$ ppr r_dying <+> ppr w_dying $$ text (show freeregs) $$ ppr assig) $ do
345 return (new_instrs, [])
347 _ -> genRaInsn block_live new_instrs id instr
348 (uniqSetToList $ liveDieRead live)
349 (uniqSetToList $ liveDieWrite live)
353 = pprPanic "raInsn" (text "no match for:" <> ppr instr)
358 genRaInsn block_live new_instrs block_id instr r_dying w_dying =
359 case regUsageOfInstr instr of { RU read written ->
361 let real_written = [ rr | (RegReal rr) <- written ]
362 let virt_written = [ vr | (RegVirtual vr) <- written ]
364 -- we don't need to do anything with real registers that are
365 -- only read by this instr. (the list is typically ~2 elements,
366 -- so using nub isn't a problem).
367 let virt_read = nub [ vr | (RegVirtual vr) <- read ]
369 -- (a) save any temporaries which will be clobbered by this instruction
370 clobber_saves <- saveClobberedTemps real_written r_dying
373 {- freeregs <- getFreeRegsR
377 $$ text "r_dying = " <+> ppr r_dying
378 $$ text "w_dying = " <+> ppr w_dying
379 $$ text "virt_read = " <+> ppr virt_read
380 $$ text "virt_written = " <+> ppr virt_written
381 $$ text "freeregs = " <+> text (show freeregs)
382 $$ text "assig = " <+> ppr assig)
386 -- (b), (c) allocate real regs for all regs read by this instruction.
387 (r_spills, r_allocd) <-
388 allocateRegsAndSpill True{-reading-} virt_read [] [] virt_read
390 -- (d) Update block map for new destinations
391 -- NB. do this before removing dead regs from the assignment, because
392 -- these dead regs might in fact be live in the jump targets (they're
393 -- only dead in the code that follows in the current basic block).
394 (fixup_blocks, adjusted_instr)
395 <- joinToTargets block_live block_id instr
397 -- (e) Delete all register assignments for temps which are read
398 -- (only) and die here. Update the free register list.
401 -- (f) Mark regs which are clobbered as unallocatable
402 clobberRegs real_written
404 -- (g) Allocate registers for temporaries *written* (only)
405 (w_spills, w_allocd) <-
406 allocateRegsAndSpill False{-writing-} virt_written [] [] virt_written
408 -- (h) Release registers for temps which are written here and not
413 -- (i) Patch the instruction
417 | (t, r) <- zip virt_read r_allocd
418 ++ zip virt_written w_allocd ]
421 = patchRegsOfInstr adjusted_instr patchLookup
424 = case lookupUFM patch_map x of
429 -- (j) free up stack slots for dead spilled regs
430 -- TODO (can't be bothered right now)
432 -- erase reg->reg moves where the source and destination are the same.
433 -- If the src temp didn't die in this instr but happened to be allocated
434 -- to the same real reg as the destination, then we can erase the move anyway.
435 let squashed_instr = case takeRegRegMoveInstr patched_instr of
440 let code = squashed_instr ++ w_spills ++ reverse r_spills
441 ++ clobber_saves ++ new_instrs
443 -- pprTrace "patched-code" ((vcat $ map (docToSDoc . pprInstr) code)) $ do
444 -- pprTrace "pached-fixup" ((ppr fixup_blocks)) $ do
446 return (code, fixup_blocks)
450 -- -----------------------------------------------------------------------------
453 releaseRegs regs = do
458 loop _ free _ | free `seq` False = undefined
459 loop assig free [] = do setAssigR assig; setFreeRegsR free; return ()
460 loop assig free (RegReal rr : rs) = loop assig (releaseReg rr free) rs
461 loop assig free (r:rs) =
462 case lookupUFM assig r of
463 Just (InBoth real _) -> loop (delFromUFM assig r) (releaseReg real free) rs
464 Just (InReg real) -> loop (delFromUFM assig r) (releaseReg real free) rs
465 _other -> loop (delFromUFM assig r) free rs
468 -- -----------------------------------------------------------------------------
469 -- Clobber real registers
471 -- For each temp in a register that is going to be clobbered:
472 -- - if the temp dies after this instruction, do nothing
473 -- - otherwise, put it somewhere safe (another reg if possible,
474 -- otherwise spill and record InBoth in the assignment).
475 -- - for allocateRegs on the temps *read*,
476 -- - clobbered regs are allocatable.
478 -- for allocateRegs on the temps *written*,
479 -- - clobbered regs are not allocatable.
481 -- TODO: instead of spilling, try to copy clobbered
482 -- temps to another register if possible.
488 => [RealReg] -- real registers clobbered by this instruction
489 -> [Reg] -- registers which are no longer live after this insn
490 -> RegM [instr] -- return: instructions to spill any temps that will
493 saveClobberedTemps [] _
496 saveClobberedTemps clobbered dying
501 | (temp, InReg reg) <- ufmToList assig
502 , any (realRegsAlias reg) clobbered
503 , temp `notElem` map getUnique dying ]
505 (instrs,assig') <- clobber assig [] to_spill
510 clobber assig instrs []
511 = return (instrs, assig)
513 clobber assig instrs ((temp, reg) : rest)
515 (spill, slot) <- spillR (RegReal reg) temp
517 -- record why this reg was spilled for profiling
518 recordSpill (SpillClobber temp)
520 let new_assign = addToUFM assig temp (InBoth reg slot)
522 clobber new_assign (spill : instrs) rest
526 -- | Mark all these regal regs as allocated,
527 -- and kick out their vreg assignments.
529 clobberRegs :: [RealReg] -> RegM ()
533 clobberRegs clobbered
535 freeregs <- getFreeRegsR
536 setFreeRegsR $! foldr allocateReg freeregs clobbered
539 setAssigR $! clobber assig (ufmToList assig)
542 -- if the temp was InReg and clobbered, then we will have
543 -- saved it in saveClobberedTemps above. So the only case
544 -- we have to worry about here is InBoth. Note that this
545 -- also catches temps which were loaded up during allocation
546 -- of read registers, not just those saved in saveClobberedTemps.
551 clobber assig ((temp, InBoth reg slot) : rest)
552 | any (realRegsAlias reg) clobbered
553 = clobber (addToUFM assig temp (InMem slot)) rest
555 clobber assig (_:rest)
558 -- -----------------------------------------------------------------------------
559 -- allocateRegsAndSpill
561 -- This function does several things:
562 -- For each temporary referred to by this instruction,
563 -- we allocate a real register (spilling another temporary if necessary).
564 -- We load the temporary up from memory if necessary.
565 -- We also update the register assignment in the process, and
566 -- the list of free registers and free stack slots.
570 => Bool -- True <=> reading (load up spilled regs)
571 -> [VirtualReg] -- don't push these out
572 -> [instr] -- spill insns
573 -> [RealReg] -- real registers allocated (accum.)
574 -> [VirtualReg] -- temps to allocate
578 allocateRegsAndSpill _ _ spills alloc []
579 = return (spills, reverse alloc)
581 allocateRegsAndSpill reading keep spills alloc (r:rs)
582 = do assig <- getAssigR
583 case lookupUFM assig r of
584 -- case (1a): already in a register
585 Just (InReg my_reg) ->
586 allocateRegsAndSpill reading keep spills (my_reg:alloc) rs
588 -- case (1b): already in a register (and memory)
589 -- NB1. if we're writing this register, update its assignemnt to be
590 -- InReg, because the memory value is no longer valid.
591 -- NB2. This is why we must process written registers here, even if they
592 -- are also read by the same instruction.
593 Just (InBoth my_reg _)
594 -> do when (not reading) (setAssigR (addToUFM assig r (InReg my_reg)))
595 allocateRegsAndSpill reading keep spills (my_reg:alloc) rs
597 -- Not already in a register, so we need to find a free one...
598 loc -> allocRegsAndSpill_spill reading keep spills alloc r rs loc assig
601 allocRegsAndSpill_spill reading keep spills alloc r rs loc assig
603 freeRegs <- getFreeRegsR
604 let freeRegs_thisClass = getFreeRegs (classOfVirtualReg r) freeRegs
606 case freeRegs_thisClass of
608 -- case (2): we have a free register
610 do spills' <- loadTemp reading r loc my_reg spills
613 -- if the tmp was in a slot, then now its in a reg as well
614 | Just (InMem slot) <- loc
618 -- tmp has been loaded into a reg
622 setAssigR (addToUFM assig r $! new_loc)
623 setFreeRegsR $ allocateReg my_reg freeRegs
625 allocateRegsAndSpill reading keep spills' (my_reg : alloc) rs
628 -- case (3): we need to push something out to free up a register
630 do let keep' = map getUnique keep
632 -- the vregs we could kick out that are already in a slot
633 let candidates_inBoth
635 | (temp, InBoth reg mem) <- ufmToList assig
636 , temp `notElem` keep'
637 , targetClassOfRealReg reg == classOfVirtualReg r ]
639 -- the vregs we could kick out that are only in a reg
640 -- this would require writing the reg to a new slot before using it.
643 | (temp, InReg reg) <- ufmToList assig
644 , temp `notElem` keep'
645 , targetClassOfRealReg reg == classOfVirtualReg r ]
649 -- we have a temporary that is in both register and mem,
650 -- just free up its register for use.
651 | (temp, my_reg, slot) : _ <- candidates_inBoth
652 = do spills' <- loadTemp reading r loc my_reg spills
653 let assig1 = addToUFM assig temp (InMem slot)
654 let assig2 = addToUFM assig1 r (InReg my_reg)
657 allocateRegsAndSpill reading keep spills' (my_reg:alloc) rs
659 -- otherwise, we need to spill a temporary that currently
660 -- resides in a register.
661 | (temp_to_push_out, (my_reg :: RealReg)) : _
664 (spill_insn, slot) <- spillR (RegReal my_reg) temp_to_push_out
665 let spill_store = (if reading then id else reverse)
666 [ -- COMMENT (fsLit "spill alloc")
669 -- record that this temp was spilled
670 recordSpill (SpillAlloc temp_to_push_out)
672 -- update the register assignment
673 let assig1 = addToUFM assig temp_to_push_out (InMem slot)
674 let assig2 = addToUFM assig1 r (InReg my_reg)
677 -- if need be, load up a spilled temp into the reg we've just freed up.
678 spills' <- loadTemp reading r loc my_reg spills
680 allocateRegsAndSpill reading keep
681 (spill_store ++ spills')
685 -- there wasn't anything to spill, so we're screwed.
687 = pprPanic ("RegAllocLinear.allocRegsAndSpill: no spill candidates\n")
689 [ text "allocating vreg: " <> text (show r)
690 , text "assignment: " <> text (show $ ufmToList assig)
691 , text "freeRegs: " <> text (show freeRegs)
692 , text "initFreeRegs: " <> text (show initFreeRegs) ]
697 -- | Load up a spilled temporary if we need to.
701 -> VirtualReg -- the temp being loaded
702 -> Maybe Loc -- the current location of this temp
703 -> RealReg -- the hreg to load the temp into
707 loadTemp True vreg (Just (InMem slot)) hreg spills
709 insn <- loadR (RegReal hreg) slot
710 recordSpill (SpillLoad $ getUnique vreg)
711 return $ {- COMMENT (fsLit "spill load") : -} insn : spills
713 loadTemp _ _ _ _ spills =