CmmBuildInfoTables.hs 13.3 KB
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{-# LANGUAGE GADTs, NoMonoLocalBinds #-}
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{-# OPTIONS -fno-warn-tabs #-}
-- The above warning supression flag is a temporary kludge.
-- While working on this module you are encouraged to remove it and
-- detab the module (please do the detabbing in a separate patch). See
--     http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#TabsvsSpaces
-- for details

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-- Norman likes local bindings
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-- If this module lives on I'd like to get rid of the NoMonoLocalBinds
-- extension in due course
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-- Todo: remove -fno-warn-warnings-deprecations
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{-# OPTIONS_GHC -fno-warn-warnings-deprecations #-}
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module CmmBuildInfoTables
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    ( CAFSet, CAFEnv, cafAnal, localCAFInfo, mkTopCAFInfo
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    , setInfoTableSRT
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    , TopSRT, emptySRT, srtToData
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    , bundleCAFs
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    ) where
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#include "HsVersions.h"

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-- These should not be imported here!
import StgCmmUtils

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import Digraph
import qualified Prelude as P
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import Prelude hiding (succ)
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import BlockId
import Bitmap
import CLabel
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import Cmm
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import CmmUtils
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import IdInfo
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import Data.List
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import Maybes
import Name
import Outputable
import SMRep
import UniqSupply
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import Hoopl
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import Data.Map (Map)
import qualified Data.Map as Map
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import Data.Set (Set)
import qualified Data.Set as Set
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foldSet :: (a -> b -> b) -> b -> Set a -> b
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#if __GLASGOW_HASKELL__ < 704
foldSet = Set.fold
#else
foldSet = Set.foldr
#endif

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----------------------------------------------------------------
-- Building InfoTables


-----------------------------------------------------------------------
-- SRTs

-- WE NEED AN EXAMPLE HERE.
-- IN PARTICULAR, WE NEED TO POINT OUT THE DISTINCTION BETWEEN
-- FUNCTIONS WITH STATIC CLOSURES AND THOSE THAT MUST BE CONSTRUCTED
-- DYNAMICALLY (AND HENCE CAN'T BE REFERENCED IN AN SRT).
-- IN THE LATTER CASE, WE HAVE TO TAKE ALL THE CAFs REFERENCED BY
-- THE CLOSURE AND INLINE THEM INTO ANY SRT THAT MAY MENTION THE CLOSURE.
-- (I.E. TAKE THE TRANSITIVE CLOSURE, but only for non-static closures).

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{- EXAMPLE

f = \x. ... g ...
  where
    g = \y. ... h ... c1 ...
    h = \z. ... c2 ...

c1 & c2 are CAFs

g and h are local functions, but they have no static closures.  When
we generate code for f, we start with a CmmGroup of four CmmDecls:

   [ f_closure, f_entry, g_entry, h_entry ]

we process each CmmDecl separately in cpsTop, giving us a list of
CmmDecls. e.g. for f_entry, we might end up with

   [ f_entry, f1_ret, f2_proc ]

where f1_ret is a return point, and f2_proc is a proc-point.  We have
a CAFSet for each of these CmmDecls, let's suppose they are

   [ f_entry{g_closure}, f1_ret{g_closure}, f2_proc{} ]
   [ g_entry{h_closure, c1_closure} ]
   [ h_entry{c2_closure} ]

Now, note that we cannot use g_closure and h_closure in an SRT,
because there are no static closures corresponding to these functions.
So we have to flatten out the structure, replacing g_closure and
h_closure with their contents:

   [ f_entry{c2_closure, c1_closure}, f1_ret{c2_closure,c1_closure}, f2_proc{} ]
   [ g_entry{c2_closure, c1_closure} ]
   [ h_entry{c2_closure} ]

This is what mkTopCAFInfo is doing.

-}
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-----------------------------------------------------------------------
-- Finding the CAFs used by a procedure

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type CAFSet = Set CLabel
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type CAFEnv = BlockEnv CAFSet

-- First, an analysis to find live CAFs.
cafLattice :: DataflowLattice CAFSet
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cafLattice = DataflowLattice "live cafs" Set.empty add
  where add _ (OldFact old) (NewFact new) = case old `Set.union` new of
                                              new' -> (changeIf $ Set.size new' > Set.size old, new')
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cafTransfers :: BwdTransfer CmmNode CAFSet
cafTransfers = mkBTransfer3 first middle last
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  where first  _ live = live
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        middle m live = foldExpDeep addCaf m live
        last   l live = foldExpDeep addCaf l (joinOutFacts cafLattice l live)
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        addCaf e set = case e of
               CmmLit (CmmLabel c)              -> add c set
               CmmLit (CmmLabelOff c _)         -> add c set
               CmmLit (CmmLabelDiffOff c1 c2 _) -> add c1 $ add c2 set
               _ -> set
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        add l s = if hasCAF l then Set.insert (toClosureLbl l) s
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                              else s
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cafAnal :: CmmGraph -> CAFEnv
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cafAnal g = dataflowAnalBwd g [] $ analBwd cafLattice cafTransfers
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-----------------------------------------------------------------------
-- Building the SRTs

-- Description of the SRT for a given module.
-- Note that this SRT may grow as we greedily add new CAFs to it.
data TopSRT = TopSRT { lbl      :: CLabel
                     , next_elt :: Int -- the next entry in the table
                     , rev_elts :: [CLabel]
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                     , elt_map  :: Map CLabel Int }
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                        -- map: CLabel -> its last entry in the table
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instance Outputable TopSRT where
  ppr (TopSRT lbl next elts eltmap) =
    text "TopSRT:" <+> ppr lbl
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                   <+> ppr next
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                   <+> ppr elts
                   <+> ppr eltmap
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emptySRT :: MonadUnique m => m TopSRT
emptySRT =
  do top_lbl <- getUniqueM >>= \ u -> return $ mkSRTLabel (mkFCallName u "srt") NoCafRefs
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     return TopSRT { lbl = top_lbl, next_elt = 0, rev_elts = [], elt_map = Map.empty }
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cafMember :: TopSRT -> CLabel -> Bool
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cafMember srt lbl = Map.member lbl (elt_map srt)
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cafOffset :: TopSRT -> CLabel -> Maybe Int
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cafOffset srt lbl = Map.lookup lbl (elt_map srt)
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addCAF :: CLabel -> TopSRT -> TopSRT
addCAF caf srt =
  srt { next_elt = last + 1
      , rev_elts = caf : rev_elts srt
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      , elt_map  = Map.insert caf last (elt_map srt) }
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    where last  = next_elt srt

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srtToData :: TopSRT -> CmmGroup
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srtToData srt = [CmmData RelocatableReadOnlyData (Statics (lbl srt) tbl)]
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    where tbl = map (CmmStaticLit . CmmLabel) (reverse (rev_elts srt))

-- Once we have found the CAFs, we need to do two things:
-- 1. Build a table of all the CAFs used in the procedure.
-- 2. Compute the C_SRT describing the subset of CAFs live at each procpoint.
--
-- When building the local view of the SRT, we first make sure that all the CAFs are 
-- in the SRT. Then, if the number of CAFs is small enough to fit in a bitmap,
-- we make sure they're all close enough to the bottom of the table that the
-- bitmap will be able to cover all of them.
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buildSRTs :: TopSRT -> Map CLabel CAFSet -> CAFSet ->
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             UniqSM (TopSRT, Maybe CmmDecl, C_SRT)
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buildSRTs topSRT topCAFMap cafs =
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  do let liftCAF lbl z = -- get CAFs for functions without static closures
           case Map.lookup lbl topCAFMap of Just cafs -> z `Set.union` cafs
                                            Nothing   -> Set.insert lbl z
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         -- For each label referring to a function f without a static closure,
         -- replace it with the CAFs that are reachable from f.
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         sub_srt topSRT localCafs =
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           let cafs = Set.elems (foldSet liftCAF Set.empty localCafs)
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               mkSRT topSRT =
                 do localSRTs <- procpointSRT (lbl topSRT) (elt_map topSRT) cafs
                    return (topSRT, localSRTs)
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           in if length cafs > maxBmpSize then
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                mkSRT (foldl add_if_missing topSRT cafs)
              else -- make sure all the cafs are near the bottom of the srt
                mkSRT (add_if_too_far topSRT cafs)
         add_if_missing srt caf =
           if cafMember srt caf then srt else addCAF caf srt
         -- If a CAF is more than maxBmpSize entries from the young end of the
         -- SRT, then we add it to the SRT again.
         -- (Note: Not in the SRT => infinitely far.)
         add_if_too_far srt@(TopSRT {elt_map = m}) cafs =
           add srt (sortBy farthestFst cafs)
             where
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               farthestFst x y = case (Map.lookup x m, Map.lookup y m) of
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                                   (Nothing, Nothing) -> EQ
                                   (Nothing, Just _)  -> LT
                                   (Just _,  Nothing) -> GT
                                   (Just d, Just d')  -> compare d' d
               add srt [] = srt
               add srt@(TopSRT {next_elt = next}) (caf : rst) =
                 case cafOffset srt caf of
                   Just ix -> if next - ix > maxBmpSize then
                                add (addCAF caf srt) rst
                              else srt
                   Nothing -> add (addCAF caf srt) rst
     (topSRT, subSRTs) <- sub_srt topSRT cafs
     let (sub_tbls, blockSRTs) = subSRTs
     return (topSRT, sub_tbls, blockSRTs)

-- Construct an SRT bitmap.
-- Adapted from simpleStg/SRT.lhs, which expects Id's.
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procpointSRT :: CLabel -> Map CLabel Int -> [CLabel] ->
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                UniqSM (Maybe CmmDecl, C_SRT)
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procpointSRT _ _ [] =
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 return (Nothing, NoC_SRT)
procpointSRT top_srt top_table entries =
 do (top, srt) <- bitmap `seq` to_SRT top_srt offset len bitmap
    return (top, srt)
  where
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    ints = map (expectJust "constructSRT" . flip Map.lookup top_table) entries
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    sorted_ints = sort ints
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    offset = head sorted_ints
    bitmap_entries = map (subtract offset) sorted_ints
    len = P.last bitmap_entries + 1
    bitmap = intsToBitmap len bitmap_entries

maxBmpSize :: Int
maxBmpSize = widthInBits wordWidth `div` 2

-- Adapted from codeGen/StgCmmUtils, which converts from SRT to C_SRT.
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to_SRT :: CLabel -> Int -> Int -> Bitmap -> UniqSM (Maybe CmmDecl, C_SRT)
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to_SRT top_srt off len bmp
  | len > maxBmpSize || bmp == [fromIntegral srt_escape]
  = do id <- getUniqueM
       let srt_desc_lbl = mkLargeSRTLabel id
           tbl = CmmData RelocatableReadOnlyData $
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                   Statics srt_desc_lbl $ map CmmStaticLit
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                     ( cmmLabelOffW top_srt off
                     : mkWordCLit (fromIntegral len)
                     : map mkWordCLit bmp)
       return (Just tbl, C_SRT srt_desc_lbl 0 srt_escape)
  | otherwise
  = return (Nothing, C_SRT top_srt off (fromIntegral (head bmp)))
	-- The fromIntegral converts to StgHalfWord

-- Gather CAF info for a procedure, but only if the procedure
-- doesn't have a static closure.
-- (If it has a static closure, it will already have an SRT to
--  keep its CAFs live.)
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-- Any procedure referring to a non-static CAF c must keep live
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-- any CAF that is reachable from c.
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localCAFInfo :: CAFEnv -> CmmDecl -> Maybe (CLabel, CAFSet)
localCAFInfo _      (CmmData _ _) = Nothing
localCAFInfo cafEnv (CmmProc top_info top_l (CmmGraph {g_entry=entry})) =
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  case info_tbl top_info of
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    CmmInfoTable { cit_rep = rep } 
      | not (isStaticRep rep) 
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      -> Just (toClosureLbl top_l,
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               expectJust "maybeBindCAFs" $ mapLookup entry cafEnv)
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    _ -> Nothing

-- Once we have the local CAF sets for some (possibly) mutually
-- recursive functions, we can create an environment mapping
-- each function to its set of CAFs. Note that a CAF may
-- be a reference to a function. If that function f does not have
-- a static closure, then we need to refer specifically
-- to the set of CAFs used by f. Of course, the set of CAFs
-- used by f must be included in the local CAF sets that are input to
-- this function. To minimize lookup time later, we return
-- the environment with every reference to f replaced by its set of CAFs.
-- To do this replacement efficiently, we gather strongly connected
-- components, then we sort the components in topological order.
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mkTopCAFInfo :: [(CLabel, CAFSet)] -> Map CLabel CAFSet
mkTopCAFInfo localCAFs = foldl addToTop Map.empty g
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  where addToTop env (AcyclicSCC (l, cafset)) =
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          Map.insert l (flatten env cafset) env
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        addToTop env (CyclicSCC nodes) =
          let (lbls, cafsets) = unzip nodes
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              cafset  = foldr Set.delete (foldl Set.union Set.empty cafsets) lbls
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          in foldl (\env l -> Map.insert l (flatten env cafset) env) env lbls
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        flatten env cafset = foldSet (lookup env) Set.empty cafset
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        lookup env caf cafset' =
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          case Map.lookup caf env of Just cafs -> foldSet add cafset' cafs
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                                     Nothing -> add caf cafset'
        add caf cafset' = Set.insert caf cafset'
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        g = stronglyConnCompFromEdgedVertices
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              (map (\n@(l, cafs) -> (n, l, Set.elems cafs)) localCAFs)
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-- Bundle the CAFs used at a procpoint.
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bundleCAFs :: CAFEnv -> CmmDecl -> (CAFSet, CmmDecl)
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bundleCAFs cafEnv t@(CmmProc _ _ (CmmGraph {g_entry=entry})) =
  (expectJust "bundleCAFs" (mapLookup entry cafEnv), t)
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bundleCAFs _ t = (Set.empty, t)
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-- Construct the SRTs for the given procedure.
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setInfoTableSRT :: Map CLabel CAFSet -> TopSRT -> (CAFSet, CmmDecl) ->
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                   UniqSM (TopSRT, [CmmDecl])
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setInfoTableSRT topCAFMap topSRT (cafs, t) =
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  setSRT cafs topCAFMap topSRT t

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setSRT :: CAFSet -> Map CLabel CAFSet -> TopSRT ->
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          CmmDecl -> UniqSM (TopSRT, [CmmDecl])
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setSRT cafs topCAFMap topSRT t =
  do (topSRT, cafTable, srt) <- buildSRTs topSRT topCAFMap cafs
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     let t' = updInfo id (const srt) t
     case cafTable of
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       Just tbl -> return (topSRT, [t', tbl])
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       Nothing  -> return (topSRT, [t'])

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type StackLayout = Liveness

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updInfo :: (StackLayout -> StackLayout) -> (C_SRT -> C_SRT) -> CmmDecl -> CmmDecl
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updInfo toVars toSrt (CmmProc top_info top_l g) =
  CmmProc (top_info {info_tbl=updInfoTbl toVars toSrt (info_tbl top_info)}) top_l g
updInfo _ _ t = t

updInfoTbl :: (StackLayout -> StackLayout) -> (C_SRT -> C_SRT) -> CmmInfoTable -> CmmInfoTable
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updInfoTbl toVars toSrt info_tbl@(CmmInfoTable {})
  = info_tbl { cit_srt = toSrt (cit_srt info_tbl)
             , cit_rep = case cit_rep info_tbl of
                           StackRep ls -> StackRep (toVars ls)
                           other       -> other }
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updInfoTbl _ _ t@CmmNonInfoTable = t