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|
----------------------------------------------------------------------
-- |
-- Module : Subexpressions
-- Maintainer : AR
-- Stability : (stable)
-- Portability : (portable)
--
-- > CVS $Date: 2005/09/20 09:32:56 $
-- > CVS $Author: aarne $
-- > CVS $Revision: 1.4 $
--
-- Common subexpression elimination.
-- all tables. AR 18\/9\/2005.
-----------------------------------------------------------------------------
module GF.Canon.Subexpressions (
elimSubtermsMod, prSubtermStat, unSubelimCanon, unSubelimModule
) where
import GF.Canon.AbsGFC
import GF.Infra.Ident
import GF.Canon.GFC
import GF.Canon.Look
import GF.Grammar.PrGrammar
import GF.Canon.CMacros as C
import GF.Data.Operations
import qualified GF.Infra.Modules as M
import Control.Monad
import Data.Map (Map)
import qualified Data.Map as Map
import Data.List
{-
This module implements a simple common subexpression elimination
for gfc grammars, to factor out shared subterms in lin rules.
It works in three phases:
(1) collectSubterms collects recursively all subterms of forms table and (P x..y)
from lin definitions (experience shows that only these forms
tend to get shared) and counts how many times they occur
(2) addSubexpConsts takes those subterms t that occur more than once
and creates definitions of form "oper A''n = t" where n is a
fresh number; notice that we assume no ids of this form are in
scope otherwise
(3) elimSubtermsMod goes through lins and the created opers by replacing largest
possible subterms by the newly created identifiers
The optimization is invoked in gf by the flag i -subs.
If an application does not support GFC opers, the effect of this
optimization can be undone by the function unSubelimCanon.
The function unSubelimCanon can be used to diagnostisize how much
cse is possible in the grammar. It is used by the flag pg -printer=subs.
-}
-- exported functions
elimSubtermsMod :: (Ident,CanonModInfo) -> Err (Ident, CanonModInfo)
elimSubtermsMod (mo,m) = case m of
M.ModMod (M.Module mt st fs me ops js) -> do
(tree,_) <- appSTM (getSubtermsMod mo (tree2list js)) (Map.empty,0)
js2 <- liftM buildTree $ addSubexpConsts mo tree $ tree2list js
return (mo,M.ModMod (M.Module mt st fs me ops js2))
_ -> return (mo,m)
prSubtermStat :: CanonGrammar -> String
prSubtermStat gr = unlines [prt mo ++++ expsIn mo js | (mo,js) <- mos] where
mos = [(i, tree2list (M.jments m)) | (i, M.ModMod m) <- M.modules gr, M.isModCnc m]
expsIn mo js = err id id $ do
(tree,_) <- appSTM (getSubtermsMod mo js) (Map.empty,0)
let list0 = Map.toList tree
let list1 = sortBy (\ (_,(m,_)) (_,(n,_)) -> compare n m) list0
return $ unlines [show n ++ "\t" ++ prt trm | (trm,(n,_)) <- list1]
unSubelimCanon :: CanonGrammar -> CanonGrammar
unSubelimCanon gr@(M.MGrammar modules) =
M.MGrammar $ map unSubelimModule modules
unSubelimModule :: CanonModule -> CanonModule
unSubelimModule mo@(i,m) = case m of
M.ModMod (M.Module mt@(M.MTConcrete _) st fs me ops js) | hasSub ljs ->
(i, M.ModMod (M.Module mt st fs me ops
(rebuild (map unparInfo ljs))))
where ljs = tree2list js
_ -> (i,m)
where
-- perform this iff the module has opers
hasSub ljs = not $ null [c | (c,ResOper _ _) <- ljs]
unparInfo (c,info) = case info of
CncFun k xs t m -> [(c, CncFun k xs (unparTerm t) m)]
ResOper _ _ -> []
_ -> [(c,info)]
unparTerm t = case t of
I c -> errVal t $ liftM unparTerm $ lookupGlobal gr c
_ -> C.composSafeOp unparTerm t
gr = M.MGrammar [mo]
rebuild = buildTree . concat
-- implementation
type TermList = Map Term (Int,Int) -- number of occs, id
type TermM a = STM (TermList,Int) a
addSubexpConsts :: Ident -> Map Term (Int,Int) -> [(Ident,Info)] -> Err [(Ident,Info)]
addSubexpConsts mo tree lins = do
let opers = [oper id trm | (trm,(_,id)) <- list]
mapM mkOne $ opers ++ lins
where
mkOne (f,def) = case def of
CncFun ci xs trm pn -> do
trm' <- recomp f trm
return (f,CncFun ci xs trm' pn)
ResOper ty trm -> do
trm' <- recomp f trm
return (f,ResOper ty trm')
_ -> return (f,def)
recomp f t = case Map.lookup t tree of
Just (_,id) | ident id /= f -> return $ I $ cident mo id
_ -> composOp (recomp f) t
list = Map.toList tree
oper id trm = (ident id, ResOper TStr trm) --- type TStr does not matter
getSubtermsMod :: Ident -> [(Ident,Info)] -> TermM (Map Term (Int,Int))
getSubtermsMod mo js = do
mapM (getInfo (collectSubterms mo)) js
(tree0,_) <- readSTM
return $ Map.filter (\ (nu,_) -> nu > 1) tree0
where
getInfo get fi@(f,i) = case i of
CncFun ci xs trm pn -> do
get trm
return $ fi
ResOper ty trm -> do
get trm
return $ fi
_ -> return fi
collectSubterms :: Ident -> Term -> TermM Term
collectSubterms mo t = case t of
Par _ (_:_) -> add t
T ty cs -> do
let (ps,ts) = unzip [(p,t) | Cas p t <- cs]
mapM (collectSubterms mo) ts
add t
V ty ts -> do
mapM (collectSubterms mo) ts
add t
K (KP _ _) -> add t
_ -> composOp (collectSubterms mo) t
where
add t = do
(ts,i) <- readSTM
let
((count,id),next) = case Map.lookup t ts of
Just (nu,id) -> ((nu+1,id), i)
_ -> ((1, i ), i+1)
writeSTM (Map.insert t (count,id) ts, next)
return t --- only because of composOp
ident :: Int -> Ident
ident i = identC ("A''" ++ show i) ---
cident :: Ident -> Int -> CIdent
cident mo = CIQ mo . ident
|
