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
99 import RegAlloc.Liveness
107 import Cmm hiding (RegSet)
121 #include "../includes/MachRegs.h"
124 -- -----------------------------------------------------------------------------
125 -- Top level of the register allocator
127 -- Allocate registers
130 -> UniqSM (NatCmmTop, Maybe RegAllocStats)
132 regAlloc (CmmData sec d)
137 regAlloc (CmmProc (LiveInfo info _ _) lbl params (ListGraph []))
138 = return ( CmmProc info lbl params (ListGraph [])
141 regAlloc (CmmProc static lbl params (ListGraph comps))
142 | LiveInfo info (Just first_id) block_live <- static
144 -- do register allocation on each component.
145 (final_blocks, stats)
146 <- linearRegAlloc first_id block_live
147 $ map (\b -> case b of
148 BasicBlock _ [b] -> AcyclicSCC b
149 BasicBlock _ bs -> CyclicSCC bs)
152 -- make sure the block that was first in the input list
153 -- stays at the front of the output
154 let ((first':_), rest')
155 = partition ((== first_id) . blockId) final_blocks
157 return ( CmmProc info lbl params (ListGraph (first' : rest'))
160 -- bogus. to make non-exhaustive match warning go away.
161 regAlloc (CmmProc _ _ _ _)
162 = panic "RegAllocLinear.regAlloc: no match"
165 -- -----------------------------------------------------------------------------
166 -- Linear sweep to allocate registers
169 -- | Do register allocation on some basic blocks.
170 -- But be careful to allocate a block in an SCC only if it has
171 -- an entry in the block map or it is the first block.
174 :: BlockId -- ^ the first block
175 -> BlockMap RegSet -- ^ live regs on entry to each basic block
176 -> [SCC LiveBasicBlock] -- ^ instructions annotated with "deaths"
177 -> UniqSM ([NatBasicBlock], RegAllocStats)
179 linearRegAlloc first_id block_live sccs
181 let (_, _, stats, blocks) =
182 runR emptyBlockMap initFreeRegs emptyRegMap emptyStackMap us
183 $ linearRA_SCCs first_id block_live [] sccs
185 return (blocks, stats)
187 linearRA_SCCs _ _ blocksAcc []
188 = return $ reverse blocksAcc
190 linearRA_SCCs first_id block_live blocksAcc (AcyclicSCC block : sccs)
191 = do blocks' <- processBlock block_live block
192 linearRA_SCCs first_id block_live
193 ((reverse blocks') ++ blocksAcc)
196 linearRA_SCCs first_id block_live blocksAcc (CyclicSCC blocks : sccs)
197 = do let process [] [] accum = return $ reverse accum
198 process [] next_round accum = process next_round [] accum
199 process (b@(BasicBlock id _) : blocks) next_round accum =
200 do block_assig <- getBlockAssigR
201 if isJust (lookupBlockEnv block_assig id) || id == first_id
202 then do b' <- processBlock block_live b
203 process blocks next_round (b' : accum)
204 else process blocks (b : next_round) accum
205 blockss' <- process blocks [] (return [])
206 linearRA_SCCs first_id block_live
207 (reverse (concat blockss') ++ blocksAcc)
211 -- | Do register allocation on this basic block
214 :: BlockMap RegSet -- ^ live regs on entry to each basic block
215 -> LiveBasicBlock -- ^ block to do register allocation on
216 -> RegM [NatBasicBlock] -- ^ block with registers allocated
218 processBlock block_live (BasicBlock id instrs)
221 <- linearRA block_live [] [] id instrs
223 return $ BasicBlock id instrs' : fixups
226 -- | Load the freeregs and current reg assignment into the RegM state
227 -- for the basic block with this BlockId.
228 initBlock :: BlockId -> RegM ()
230 = do block_assig <- getBlockAssigR
231 case lookupBlockEnv block_assig id of
232 -- no prior info about this block: assume everything is
233 -- free and the assignment is empty.
235 -> do setFreeRegsR initFreeRegs
236 setAssigR emptyRegMap
238 -- load info about register assignments leading into this block.
239 Just (freeregs, assig)
240 -> do setFreeRegsR freeregs
244 -- | Do allocation for a sequence of instructions.
246 :: BlockMap RegSet -- ^ map of what vregs are live on entry to each block.
247 -> [Instr] -- ^ accumulator for instructions already processed.
248 -> [NatBasicBlock] -- ^ accumulator for blocks of fixup code.
249 -> BlockId -- ^ id of the current block, for debugging.
250 -> [LiveInstr] -- ^ liveness annotated instructions in this block.
252 -> RegM ( [Instr] -- instructions after register allocation
253 , [NatBasicBlock]) -- fresh blocks of fixup code.
256 linearRA _ accInstr accFixup _ []
258 ( reverse accInstr -- instrs need to be returned in the correct order.
259 , accFixup) -- it doesn't matter what order the fixup blocks are returned in.
262 linearRA block_live accInstr accFixups id (instr:instrs)
264 (accInstr', new_fixups)
265 <- raInsn block_live accInstr id instr
267 linearRA block_live accInstr' (new_fixups ++ accFixups) id instrs
270 -- | Do allocation for a single instruction.
272 :: BlockMap RegSet -- ^ map of what vregs are love on entry to each block.
273 -> [Instr] -- ^ accumulator for instructions already processed.
274 -> BlockId -- ^ the id of the current block, for debugging
275 -> LiveInstr -- ^ the instr to have its regs allocated, with liveness info.
277 ( [Instr] -- new instructions
278 , [NatBasicBlock]) -- extra fixup blocks
280 raInsn _ new_instrs _ (Instr (COMMENT _) Nothing)
281 = return (new_instrs, [])
283 raInsn _ new_instrs _ (Instr (DELTA n) Nothing)
286 return (new_instrs, [])
288 raInsn block_live new_instrs id (Instr instr (Just live))
292 -- If we have a reg->reg move between virtual registers, where the
293 -- src register is not live after this instruction, and the dst
294 -- register does not already have an assignment,
295 -- and the source register is assigned to a register, not to a spill slot,
296 -- then we can eliminate the instruction.
297 -- (we can't eliminitate it if the source register is on the stack, because
298 -- we do not want to use one spill slot for different virtual registers)
299 case isRegRegMove instr of
300 Just (src,dst) | src `elementOfUniqSet` (liveDieRead live),
302 not (dst `elemUFM` assig),
303 Just (InReg _) <- (lookupUFM assig src) -> do
305 RealReg i -> setAssigR (addToUFM assig dst (InReg i))
306 -- if src is a fixed reg, then we just map dest to this
307 -- reg in the assignment. src must be an allocatable reg,
308 -- otherwise it wouldn't be in r_dying.
309 _virt -> case lookupUFM assig src of
310 Nothing -> panic "raInsn"
312 setAssigR (addToUFM (delFromUFM assig src) dst loc)
314 -- we have eliminated this instruction
316 freeregs <- getFreeRegsR
318 pprTrace "raInsn" (text "ELIMINATED: " <> docToSDoc (pprInstr instr)
319 $$ ppr r_dying <+> ppr w_dying $$ text (show freeregs) $$ ppr assig) $ do
321 return (new_instrs, [])
323 _ -> genRaInsn block_live new_instrs id instr
324 (uniqSetToList $ liveDieRead live)
325 (uniqSetToList $ liveDieWrite live)
329 = pprPanic "raInsn" (text "no match for:" <> ppr instr)
334 genRaInsn block_live new_instrs block_id instr r_dying w_dying =
335 case regUsage instr of { RU read written ->
336 case partition isRealReg written of { (real_written1,virt_written) ->
339 real_written = [ r | RealReg r <- real_written1 ]
341 -- we don't need to do anything with real registers that are
342 -- only read by this instr. (the list is typically ~2 elements,
343 -- so using nub isn't a problem).
344 virt_read = nub (filter isVirtualReg read)
347 -- (a) save any temporaries which will be clobbered by this instruction
348 clobber_saves <- saveClobberedTemps real_written r_dying
351 {- freeregs <- getFreeRegsR
354 (docToSDoc (pprInstr instr) $$ ppr r_dying <+> ppr w_dying $$ ppr virt_read <+> ppr virt_written
355 $$ text (show freeregs) $$ ppr assig)
359 -- (b), (c) allocate real regs for all regs read by this instruction.
360 (r_spills, r_allocd) <-
361 allocateRegsAndSpill True{-reading-} virt_read [] [] virt_read
363 -- (d) Update block map for new destinations
364 -- NB. do this before removing dead regs from the assignment, because
365 -- these dead regs might in fact be live in the jump targets (they're
366 -- only dead in the code that follows in the current basic block).
367 (fixup_blocks, adjusted_instr)
368 <- joinToTargets block_live block_id instr
370 -- (e) Delete all register assignments for temps which are read
371 -- (only) and die here. Update the free register list.
374 -- (f) Mark regs which are clobbered as unallocatable
375 clobberRegs real_written
377 -- (g) Allocate registers for temporaries *written* (only)
378 (w_spills, w_allocd) <-
379 allocateRegsAndSpill False{-writing-} virt_written [] [] virt_written
381 -- (h) Release registers for temps which are written here and not
386 -- (i) Patch the instruction
387 patch_map = listToUFM [ (t,RealReg r) |
388 (t,r) <- zip virt_read r_allocd
389 ++ zip virt_written w_allocd ]
391 patched_instr = patchRegs adjusted_instr patchLookup
392 patchLookup x = case lookupUFM patch_map x of
397 -- pprTrace "patched" (docToSDoc (pprInstr patched_instr)) $ do
399 -- (j) free up stack slots for dead spilled regs
400 -- TODO (can't be bothered right now)
402 -- erase reg->reg moves where the source and destination are the same.
403 -- If the src temp didn't die in this instr but happened to be allocated
404 -- to the same real reg as the destination, then we can erase the move anyway.
405 squashed_instr = case isRegRegMove patched_instr of
410 return (squashed_instr ++ w_spills ++ reverse r_spills
411 ++ clobber_saves ++ new_instrs,
415 -- -----------------------------------------------------------------------------
418 releaseRegs regs = do
423 loop _ free _ | free `seq` False = undefined
424 loop assig free [] = do setAssigR assig; setFreeRegsR free; return ()
425 loop assig free (RealReg r : rs) = loop assig (releaseReg r free) rs
426 loop assig free (r:rs) =
427 case lookupUFM assig r of
428 Just (InBoth real _) -> loop (delFromUFM assig r) (releaseReg real free) rs
429 Just (InReg real) -> loop (delFromUFM assig r) (releaseReg real free) rs
430 _other -> loop (delFromUFM assig r) free rs
432 -- -----------------------------------------------------------------------------
433 -- Clobber real registers
436 For each temp in a register that is going to be clobbered:
437 - if the temp dies after this instruction, do nothing
438 - otherwise, put it somewhere safe (another reg if possible,
439 otherwise spill and record InBoth in the assignment).
441 for allocateRegs on the temps *read*,
442 - clobbered regs are allocatable.
444 for allocateRegs on the temps *written*,
445 - clobbered regs are not allocatable.
449 :: [RegNo] -- real registers clobbered by this instruction
450 -> [Reg] -- registers which are no longer live after this insn
451 -> RegM [Instr] -- return: instructions to spill any temps that will
454 saveClobberedTemps [] _ = return [] -- common case
455 saveClobberedTemps clobbered dying = do
458 to_spill = [ (temp,reg) | (temp, InReg reg) <- ufmToList assig,
459 reg `elem` clobbered,
460 temp `notElem` map getUnique dying ]
462 (instrs,assig') <- clobber assig [] to_spill
466 clobber assig instrs [] = return (instrs,assig)
467 clobber assig instrs ((temp,reg):rest)
469 --ToDo: copy it to another register if possible
470 (spill,slot) <- spillR (RealReg reg) temp
471 recordSpill (SpillClobber temp)
473 let new_assign = addToUFM assig temp (InBoth reg slot)
474 clobber new_assign (spill : COMMENT (fsLit "spill clobber") : instrs) rest
476 clobberRegs :: [RegNo] -> RegM ()
477 clobberRegs [] = return () -- common case
478 clobberRegs clobbered = do
479 freeregs <- getFreeRegsR
480 -- setFreeRegsR $! foldr grabReg freeregs clobbered
481 setFreeRegsR $! foldr allocateReg freeregs clobbered
484 setAssigR $! clobber assig (ufmToList assig)
486 -- if the temp was InReg and clobbered, then we will have
487 -- saved it in saveClobberedTemps above. So the only case
488 -- we have to worry about here is InBoth. Note that this
489 -- also catches temps which were loaded up during allocation
490 -- of read registers, not just those saved in saveClobberedTemps.
491 clobber assig [] = assig
492 clobber assig ((temp, InBoth reg slot) : rest)
493 | reg `elem` clobbered
494 = clobber (addToUFM assig temp (InMem slot)) rest
495 clobber assig (_:rest)
498 -- -----------------------------------------------------------------------------
499 -- allocateRegsAndSpill
501 -- This function does several things:
502 -- For each temporary referred to by this instruction,
503 -- we allocate a real register (spilling another temporary if necessary).
504 -- We load the temporary up from memory if necessary.
505 -- We also update the register assignment in the process, and
506 -- the list of free registers and free stack slots.
509 :: Bool -- True <=> reading (load up spilled regs)
510 -> [Reg] -- don't push these out
511 -> [Instr] -- spill insns
512 -> [RegNo] -- real registers allocated (accum.)
513 -> [Reg] -- temps to allocate
514 -> RegM ([Instr], [RegNo])
516 allocateRegsAndSpill _ _ spills alloc []
517 = return (spills,reverse alloc)
519 allocateRegsAndSpill reading keep spills alloc (r:rs) = do
521 case lookupUFM assig r of
522 -- case (1a): already in a register
523 Just (InReg my_reg) ->
524 allocateRegsAndSpill reading keep spills (my_reg:alloc) rs
526 -- case (1b): already in a register (and memory)
527 -- NB1. if we're writing this register, update its assignemnt to be
528 -- InReg, because the memory value is no longer valid.
529 -- NB2. This is why we must process written registers here, even if they
530 -- are also read by the same instruction.
531 Just (InBoth my_reg _) -> do
532 when (not reading) (setAssigR (addToUFM assig r (InReg my_reg)))
533 allocateRegsAndSpill reading keep spills (my_reg:alloc) rs
535 -- Not already in a register, so we need to find a free one...
537 freeregs <- getFreeRegsR
539 case getFreeRegs (regClass r) freeregs of
541 -- case (2): we have a free register
542 my_reg:_ -> {- pprTrace "alloc" (ppr r <+> ppr my_reg <+> ppr freeClass) $ -}
544 spills' <- loadTemp reading r loc my_reg spills
546 | Just (InMem slot) <- loc, reading = InBoth my_reg slot
547 | otherwise = InReg my_reg
548 setAssigR (addToUFM assig r $! new_loc)
549 setFreeRegsR $ allocateReg my_reg freeregs
550 allocateRegsAndSpill reading keep spills' (my_reg:alloc) rs
552 -- case (3): we need to push something out to free up a register
555 keep' = map getUnique keep
556 candidates1 = [ (temp,reg,mem)
557 | (temp, InBoth reg mem) <- ufmToList assig,
558 temp `notElem` keep', regClass (RealReg reg) == regClass r ]
559 candidates2 = [ (temp,reg)
560 | (temp, InReg reg) <- ufmToList assig,
561 temp `notElem` keep', regClass (RealReg reg) == regClass r ]
563 ASSERT2(not (null candidates1 && null candidates2),
564 text (show freeregs) <+> ppr r <+> ppr assig) do
568 -- we have a temporary that is in both register and mem,
569 -- just free up its register for use.
571 (temp,my_reg,slot):_ -> do
572 spills' <- loadTemp reading r loc my_reg spills
574 assig1 = addToUFM assig temp (InMem slot)
575 assig2 = addToUFM assig1 r (InReg my_reg)
578 allocateRegsAndSpill reading keep spills' (my_reg:alloc) rs
580 -- otherwise, we need to spill a temporary that currently
581 -- resides in a register.
586 -- TODO: plenty of room for optimisation in choosing which temp
587 -- to spill. We just pick the first one that isn't used in
588 -- the current instruction for now.
590 let (temp_to_push_out, my_reg)
591 = case candidates2 of
592 [] -> panic $ "RegAllocLinear.allocRegsAndSpill: no spill candidates"
593 ++ "assignment: " ++ show (ufmToList assig) ++ "\n"
596 (spill_insn, slot) <- spillR (RealReg my_reg) temp_to_push_out
597 let spill_store = (if reading then id else reverse)
598 [ COMMENT (fsLit "spill alloc")
601 -- record that this temp was spilled
602 recordSpill (SpillAlloc temp_to_push_out)
604 -- update the register assignment
605 let assig1 = addToUFM assig temp_to_push_out (InMem slot)
606 let assig2 = addToUFM assig1 r (InReg my_reg)
609 -- if need be, load up a spilled temp into the reg we've just freed up.
610 spills' <- loadTemp reading r loc my_reg spills
612 allocateRegsAndSpill reading keep
613 (spill_store ++ spills')
617 -- | Load up a spilled temporary if we need to.
620 -> Reg -- the temp being loaded
621 -> Maybe Loc -- the current location of this temp
622 -> RegNo -- the hreg to load the temp into
626 loadTemp True vreg (Just (InMem slot)) hreg spills
628 insn <- loadR (RealReg hreg) slot
629 recordSpill (SpillLoad $ getUnique vreg)
630 return $ COMMENT (fsLit "spill load") : insn : spills
632 loadTemp _ _ _ _ spills =