breakBlock,
cmmBlockFromBrokenBlock,
blocksToBlockEnv,
+ adaptBlockToFormat,
+ selectContinuations,
+ ContFormat,
+ makeContinuationEntries,
) where
#include "HsVersions.h"
import Cmm
import CLabel
+import MachOp (MachHint(..))
import ClosureInfo
import Maybes
+import List
import Panic
+import UniqSupply
import Unique
import UniqFM
| ContinuationEntry -- ^ Return point of a function call
CmmFormals -- ^ return values (argument to continuation)
C_SRT -- ^ SRT for the continuation's info table
+ Bool -- ^ True <=> GC block so ignore stack size
| ControlEntry -- ^ Any other kind of block.
-- Only entered due to control flow.
-- no return values, but some live might end up as
-- params or possibly in the frame
+data ContFormat = ContFormat
+ CmmHintFormals -- ^ return values (argument to continuation)
+ C_SRT -- ^ SRT for the continuation's info table
+ Bool -- ^ True <=> GC block so ignore stack size
+ deriving (Eq)
-- | Final statement in a 'BlokenBlock'.
-- Constructors and arguments match those in 'Cmm',
CmmHintFormals -- ^ Results from call
-- (redundant with ContinuationEntry)
CmmActuals -- ^ Arguments to call
+ C_SRT -- ^ SRT for the continuation's info table
+ Bool -- ^ True <=> GC block so ignore stack size
| FinalSwitch -- ^ Same as a 'CmmSwitch'
CmmExpr -- ^ Scrutinee (zero based)
-- Operations for broken blocks
-----------------------------------------------------------------------------
+-- Naively breaking at *every* CmmCall leads to sub-optimal code.
+-- In particular, a CmmCall followed by a CmmBranch would result
+-- in a continuation that has the single CmmBranch statement in it.
+-- It would be better have the CmmCall directly return to the block
+-- that the branch jumps to.
+--
+-- This requires the target of the branch to look like the parameter
+-- format that the CmmCall is expecting. If other CmmCall/CmmBranch
+-- sequences go to the same place they might not be expecting the
+-- same format. So this transformation uses the following solution.
+-- First the blocks are broken up but none of the blocks are marked
+-- as continuations yet. This is the 'breakBlock' function.
+-- Second, the blocks "vote" on what other blocks need to be continuations
+-- and how they should be layed out. Plurality wins, but other selection
+-- methods could be selected at a later time.
+-- This is the 'selectContinuations' function.
+-- Finally, the blocks are upgraded to 'ContEntry' continuations
+-- based on the results with the 'makeContinuationEntries' function,
+-- and the blocks that didn't get the format they wanted for their
+-- targets get a small adaptor block created for them by
+-- the 'adaptBlockToFormat' function.
+-- could be
+
+breakProc ::
+ [BlockId] -- ^ Any GC blocks that should be special
+ -> [[Unique]] -- ^ An infinite list of uniques
+ -- to create names of the new blocks with
+ -> CmmInfo -- ^ Info table for the procedure
+ -> CLabel -- ^ Name of the procedure
+ -> CmmFormals -- ^ Parameters of the procedure
+ -> [CmmBasicBlock] -- ^ Blocks of the procecure
+ -- (First block is the entry block)
+ -> [BrokenBlock]
+
+breakProc gc_block_idents uniques info ident params blocks =
+ let
+ (adaptor_uniques : block_uniques) = uniques
+
+ broken_blocks :: ([(BlockId, ContFormat)], [BrokenBlock])
+ broken_blocks =
+ let new_blocks =
+ zipWith3 (breakBlock gc_block_idents)
+ block_uniques
+ blocks
+ (FunctionEntry info ident params :
+ repeat ControlEntry)
+ in (concatMap fst new_blocks, concatMap snd new_blocks)
+
+ selected = selectContinuations (fst broken_blocks)
+
+ in map (makeContinuationEntries selected) $
+ concat $
+ zipWith (adaptBlockToFormat selected)
+ adaptor_uniques
+ (snd broken_blocks)
+
-----------------------------------------------------------------------------
-- | Takes a 'CmmBasicBlock' and breaks it up into a list of 'BrokenBlock'
-- by splitting on each 'CmmCall' in the 'CmmBasicBlock'.
breakBlock ::
- [Unique] -- ^ An infinite list of uniques
+ [BlockId] -- ^ Any GC blocks that should be special
+ -> [Unique] -- ^ An infinite list of uniques
-- to create names of the new blocks with
-> CmmBasicBlock -- ^ Input block to break apart
-> BlockEntryInfo -- ^ Info for the first created 'BrokenBlock'
- -> [BrokenBlock]
-breakBlock uniques (BasicBlock ident stmts) entry =
+ -> ([(BlockId, ContFormat)], [BrokenBlock])
+breakBlock gc_block_idents uniques (BasicBlock ident stmts) entry =
breakBlock' uniques ident entry [] [] stmts
where
breakBlock' uniques current_id entry exits accum_stmts stmts =
-- Last statement. Make the 'BrokenBlock'
[CmmJump target arguments] ->
- [BrokenBlock current_id entry accum_stmts
- exits
- (FinalJump target arguments)]
+ ([],
+ [BrokenBlock current_id entry accum_stmts
+ exits
+ (FinalJump target arguments)])
[CmmReturn arguments] ->
- [BrokenBlock current_id entry accum_stmts
+ ([],
+ [BrokenBlock current_id entry accum_stmts
exits
- (FinalReturn arguments)]
+ (FinalReturn arguments)])
[CmmBranch target] ->
- [BrokenBlock current_id entry accum_stmts
+ ([],
+ [BrokenBlock current_id entry accum_stmts
(target:exits)
- (FinalBranch target)]
+ (FinalBranch target)])
[CmmSwitch expr targets] ->
- [BrokenBlock current_id entry accum_stmts
+ ([],
+ [BrokenBlock current_id entry accum_stmts
(mapMaybe id targets ++ exits)
- (FinalSwitch expr targets)]
+ (FinalSwitch expr targets)])
-- These shouldn't happen in the middle of a block.
-- They would cause dead code.
-- Detect this special case to remain an inverse of
-- 'cmmBlockFromBrokenBlock'
- {- TODO: Interferes with proc point detection
- [CmmCall target results arguments,
- CmmBranch next_id] -> [block]
- where
- block = do_call current_id entry accum_stmts exits next_id
- target results arguments
- -}
+ [CmmCall target results arguments (CmmSafe srt),
+ CmmBranch next_id] ->
+ ([cont_info], [block])
+ where
+ cont_info = (next_id,
+ ContFormat results srt
+ (ident `elem` gc_block_idents))
+ block = do_call current_id entry accum_stmts exits next_id
+ target results arguments srt
-- Break the block on safe calls (the main job of this function)
(CmmCall target results arguments (CmmSafe srt):stmts) ->
- block : rest
+ (cont_info : cont_infos, block : blocks)
where
next_id = BlockId $ head uniques
block = do_call current_id entry accum_stmts exits next_id
- target results arguments
- rest = breakBlock' (tail uniques) next_id
- (ContinuationEntry (map fst results) srt)
- [] [] stmts
+ target results arguments srt
+ cont_info = (next_id,
+ ContFormat results srt
+ (ident `elem` gc_block_idents))
+ (cont_infos, blocks) = breakBlock' (tail uniques) next_id
+ ControlEntry [] [] stmts
-- Default case. Just keep accumulating statements
-- and branch targets.
stmts
do_call current_id entry accum_stmts exits next_id
- target results arguments =
+ target results arguments srt =
BrokenBlock current_id entry accum_stmts (next_id:exits)
- (FinalCall next_id target results arguments)
+ (FinalCall next_id target results arguments srt
+ (current_id `elem` gc_block_idents))
cond_branch_target (CmmCondBranch _ target) = [target]
cond_branch_target _ = []
-----------------------------------------------------------------------------
+
+selectContinuations :: [(BlockId, ContFormat)] -> [(BlockId, ContFormat)]
+selectContinuations needed_continuations = formats
+ where
+ formats = map select_format format_groups
+ format_groups = groupBy by_target needed_continuations
+ by_target x y = fst x == fst y
+
+ select_format formats = winner
+ where
+ winner = head $ head $ sortBy more_votes format_votes
+ format_votes = groupBy by_format formats
+ by_format x y = snd x == snd y
+ more_votes x y = compare (length y) (length x)
+ -- sort so the most votes goes *first*
+ -- (thus the order of x and y is reversed)
+
+makeContinuationEntries formats
+ block@(BrokenBlock ident entry stmts targets exit) =
+ case lookup ident formats of
+ Nothing -> block
+ Just (ContFormat formals srt is_gc) ->
+ BrokenBlock ident (ContinuationEntry (map fst formals) srt is_gc)
+ stmts targets exit
+
+adaptBlockToFormat :: [(BlockId, ContFormat)]
+ -> Unique
+ -> BrokenBlock
+ -> [BrokenBlock]
+adaptBlockToFormat formats unique
+ block@(BrokenBlock ident entry stmts targets
+ exit@(FinalCall next target formals
+ actuals srt is_gc)) =
+ if format_formals == formals &&
+ format_srt == srt &&
+ format_is_gc == is_gc
+ then [block] -- Woohoo! This block got the continuation format it wanted
+ else [adaptor_block, revised_block]
+ -- This block didn't get the format it wanted for the
+ -- continuation, so we have to build an adaptor.
+ where
+ (ContFormat format_formals format_srt format_is_gc) =
+ maybe unknown_block id $ lookup next formats
+ unknown_block = panic "unknown block in adaptBlockToFormat"
+
+ revised_block = BrokenBlock ident entry stmts revised_targets revised_exit
+ revised_targets = adaptor_ident : delete next targets
+ revised_exit = FinalCall
+ adaptor_ident -- ^ The only part that changed
+ target formals actuals srt is_gc
+
+ adaptor_block = mk_adaptor_block adaptor_ident
+ (ContinuationEntry (map fst formals) srt is_gc)
+ next format_formals
+ adaptor_ident = BlockId unique
+
+ mk_adaptor_block :: BlockId -> BlockEntryInfo -> BlockId -> CmmHintFormals -> BrokenBlock
+ mk_adaptor_block ident entry next formals =
+ BrokenBlock ident entry [] [next] exit
+ where
+ exit = FinalJump
+ (CmmLit (CmmLabel (mkReturnPtLabel (getUnique next))))
+ (map formal_to_actual format_formals)
+
+ formal_to_actual (reg, hint) = ((CmmReg (CmmLocal reg)), hint)
+ -- TODO: Check if NoHint is right. We're
+ -- jumping to a C-- function not a foreign one
+ -- so it might always be right.
+adaptBlockToFormat _ _ block = [block]
+
+-----------------------------------------------------------------------------
-- | Convert from a BrokenBlock back to an equivalent CmmBasicBlock
-- Needed by liveness analysis
cmmBlockFromBrokenBlock :: BrokenBlock -> CmmBasicBlock
FinalReturn arguments -> [CmmReturn arguments]
FinalJump target arguments -> [CmmJump target arguments]
FinalSwitch expr targets -> [CmmSwitch expr targets]
- FinalCall branch_target call_target results arguments ->
- [CmmCall call_target results arguments (panic "needed SRT from cmmBlockFromBrokenBlock"),
+ FinalCall branch_target call_target results arguments srt _ ->
+ [CmmCall call_target results arguments (CmmSafe srt),
CmmBranch branch_target]
-----------------------------------------------------------------------------
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