X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Fcmm%2FDFMonad.hs;h=263d0d4856b3ffd70a77c01f1498ed06037438c5;hb=e239aa2329416a2822fcc03c4ed486c7d28739e1;hp=0bce264de6fc510570bc9b2c6abaf6b08e86b708;hpb=e6243a818496aad82b6f47511d3bd9bc800f747d;p=ghc-hetmet.git

diff --git a/compiler/cmm/DFMonad.hs b/compiler/cmm/DFMonad.hs
index 0bce264..263d0d4 100644
--- a/compiler/cmm/DFMonad.hs
+++ b/compiler/cmm/DFMonad.hs
@@ -45,11 +45,11 @@ conjunction with the join, so we have [[fact_add_to]]:
 -}
 
 data DataflowLattice a = DataflowLattice  { 
-  fact_name    :: String,                 -- documentation
-  fact_bot     :: a,                      -- lattice bottom element
-  fact_add_to  :: a -> a -> TxRes a,      -- lattice join and compare
+  fact_name       :: String,                 -- documentation
+  fact_bot        :: a,                      -- lattice bottom element
+  fact_add_to     :: a -> a -> TxRes a,      -- lattice join and compare
     -- ^ compute join of two args; something changed iff join is greater than 2nd arg
-  fact_do_logging :: Bool  -- log changes
+  fact_do_logging :: Bool                    -- log changes
 }
 
 
@@ -59,14 +59,14 @@ data DataflowLattice a = DataflowLattice  {
 -- case of DFM, parameterized over any monad.
 -- In practice, we apply DFM' to the FuelMonad, which provides optimization fuel and
 -- the unique supply.
-data DFState f = DFState { df_rewritten    :: ChangeFlag
-                         , df_facts        :: BlockEnv f
-                         , df_exit_fact    :: f
-                         , df_last_outs    :: [(BlockId, f)]
-                         , df_facts_change :: ChangeFlag
+data DFState f = DFState { df_rewritten    :: !ChangeFlag
+                         , df_facts        :: !(BlockEnv f)
+                         , df_exit_fact    :: !f
+                         , df_last_outs    :: ![(BlockId, f)]
+                         , df_facts_change :: !ChangeFlag
                          }
 
-newtype DFM' m fact a = DFM' (DataflowLattice fact -> DFState  fact
+newtype DFM' m fact a = DFM' (DataflowLattice fact -> DFState fact
                                                    -> m (a, DFState  fact))
 type DFM fact a = DFM' FuelMonad fact a
 
@@ -136,15 +136,11 @@ instance Monad m => DataflowAnalysis (DFM' m) where
   getExitFact = DFM' get
     where get _ s = return (df_exit_fact s, s)
   setExitFact a =
-    do old <- getExitFact
-       DataflowLattice { fact_add_to = add_fact
-                       , fact_name = name, fact_do_logging = log } <- lattice
-       case add_fact a old of
-         TxRes NoChange _ -> return ()
-         TxRes SomeChange join -> DFM' $ \_ s ->
-             let debug = if log then pprTrace else \_ _ a -> a
-             in  debug name (pprSetFact "exit" old a join) $
-                 return ((), s { df_exit_fact = join, df_facts_change = SomeChange })
+    do DataflowLattice { fact_name = name, fact_do_logging = log} <- lattice
+       DFM' $ \_ s ->
+                let debug = if log then pprTrace else \_ _ a -> a
+                in  debug name (pprSetFact "exit" a a a) $
+                    return ((), s { df_exit_fact = a })
   getAllFacts = DFM' f
     where f _ s = return (df_facts s, s)
   setAllFacts env = DFM' f
@@ -194,8 +190,12 @@ graphWasRewritten = DFM' f
                     
 instance Monad m => Monad (DFM' m f) where
   DFM' f >>= k = DFM' (\l s -> do (a, s') <- f l s
-                                  let DFM' f' = k a in f' l s')
+                                  s' `seq` case k a of DFM' f' -> f' l s')
   return a = DFM' (\_ s -> return (a, s))
+ -- The `seq` is essential to ensure that entire passes of the dataflow engine 
+ -- aren't postponed in a thunk. By making the sequence strict in the state,
+ -- we ensure that each action in the monad is executed immediately, preventing
+ -- stack overflows that previously occurred when finally forcing the old state thunks.
 
 instance FuelUsingMonad (DFM' FuelMonad f) where
   fuelRemaining = liftToDFM' fuelRemaining