X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2FsimplCore%2FFloatIn.lhs;h=6a05a98bb4fe4860ad0ce5090b5aece388f9ba2d;hb=d9fa58a35fedd36471063e4375ca177632f540e4;hp=796cddf9fa11127ab3f7822cd74610df61fa6839;hpb=bca9dd54c2b39638cb4638aaccf6015a104a1df5;p=ghc-hetmet.git

diff --git a/ghc/compiler/simplCore/FloatIn.lhs b/ghc/compiler/simplCore/FloatIn.lhs
index 796cddf..6a05a98 100644
--- a/ghc/compiler/simplCore/FloatIn.lhs
+++ b/ghc/compiler/simplCore/FloatIn.lhs
@@ -16,16 +16,16 @@ module FloatIn ( floatInwards ) where
 
 #include "HsVersions.h"
 
-import CmdLineOpts	( DynFlags, DynFlag(..), dopt )
+import CmdLineOpts	( DynFlags, DynFlag(..) )
 import CoreSyn
 import CoreUtils	( exprIsValue, exprIsDupable )
-import CoreLint		( beginPass, endPass )
+import CoreLint		( showPass, endPass )
 import CoreFVs		( CoreExprWithFVs, freeVars, freeVarsOf )
 import Id		( isOneShotLambda )
-import Var		( Id, idType, isTyVar )
+import Var		( Id, idType )
 import Type		( isUnLiftedType )
 import VarSet
-import Util		( zipEqual, zipWithEqual )
+import Util		( zipEqual, zipWithEqual, count )
 import Outputable
 \end{code}
 
@@ -37,12 +37,10 @@ floatInwards :: DynFlags -> [CoreBind] -> IO [CoreBind]
 
 floatInwards dflags binds
   = do {
-	beginPass dflags "Float inwards";
+	showPass dflags "Float inwards";
 	let { binds' = map fi_top_bind binds };
-	endPass dflags "Float inwards" 
-	 	(dopt Opt_D_verbose_core2core dflags)
+	endPass dflags "Float inwards" Opt_D_verbose_core2core binds'	
 				{- no specific flag for dumping float-in -} 
-		binds'	
     }
 			  
   where
@@ -181,16 +179,23 @@ So we treat lambda in groups, using the following rule:
 	Otherwise drop all the bindings outside the group.
 
 \begin{code}
-fiExpr to_drop (_, AnnLam b body)
-  = case collect [b] body of
-      (bndrs, real_body)
-	| all is_ok bndrs -> mkLams bndrs (fiExpr to_drop real_body)
-	| otherwise	  -> mkCoLets' to_drop (mkLams bndrs (fiExpr [] real_body))
-  where
-    collect bs (_, AnnLam b body) = collect (b:bs) body
-    collect bs body		  = (reverse bs, body)
+	-- Hack alert!  We only float in through one-shot lambdas, 
+	-- not (as you might guess) through big lambdas.  
+	-- Reason: we float *out* past big lambdas (see the test in the Lam
+	-- case of FloatOut.floatExpr) and we don't want to float straight
+	-- back in again.
+	--
+	-- It *is* important to float into one-shot lambdas, however;
+	-- see the remarks with noFloatIntoRhs.
+fiExpr to_drop lam@(_, AnnLam _ _)
+  | all is_one_shot bndrs 	-- Float in
+  = mkLams bndrs (fiExpr to_drop body)
+
+  | otherwise	 	-- Dump it all here
+  = mkCoLets' to_drop (mkLams bndrs (fiExpr [] body))
 
-    is_ok bndr = isTyVar bndr || isOneShotLambda bndr
+  where
+    (bndrs, body) = collectAnnBndrs lam
 \end{code}
 
 We don't float lets inwards past an SCC.
@@ -337,7 +342,7 @@ fiExpr to_drop (_, AnnCase scrut case_bndr alts)
     fi_alt to_drop (con, args, rhs) = (con, args, fiExpr to_drop rhs)
 
 noFloatIntoRhs (AnnNote InlineMe _) = True
-noFloatIntoRhs (AnnLam b _)   	    = not (isId b && isOneShotLambda b)
+noFloatIntoRhs (AnnLam b _)   	    = not (is_one_shot b)
 	-- IMPORTANT: don't say 'True' for a RHS with a one-shot lambda at the top.
 	-- This makes a big difference for things like
 	--	f x# = let x = I# x#
@@ -347,7 +352,9 @@ noFloatIntoRhs (AnnLam b _)   	    = not (isId b && isOneShotLambda b)
 	-- boxing constructor into it, else we box it every time which is very bad
 	-- news indeed.
 
-noFloatIntoRhs rhs = exprIsValue (deAnnotate' rhs)	-- We'd just float rigt back out again...
+noFloatIntoRhs rhs = exprIsValue (deAnnotate' rhs)	-- We'd just float right back out again...
+
+is_one_shot b = isId b && isOneShotLambda b
 \end{code}
 
 
@@ -422,7 +429,7 @@ sepBindsByDropPoint is_case drop_pts floaters
 		--	  E -> ...not mentioning x...
 
 	  n_alts      = length used_in_flags
-	  n_used_alts = length [() | True <- used_in_flags]
+	  n_used_alts = count id used_in_flags -- returns number of Trues in list.
 
 	  can_push = n_used_alts == 1		-- Used in just one branch
 		   || (is_case && 		-- We are looking at case alternatives