[project @ 2005-08-18 10:25:46 by simonpj]

1. Remove redundant coerces.  Something that started life as
	coerce a b <expr>
   might change to
	coerct Int Int <expr>
   after the types a,b are instantiated.

2. Get rid of the "bad eta expand" message. It can happen entirely legitimately.
   See comments in CoreUtils with eta_expand.

	MERGE TO STABLE

diff --git a/ghc/compiler/coreSyn/CoreUtils.lhs b/ghc/compiler/coreSyn/CoreUtils.lhs
index a8c7eae..8aba9b1 100644 (file)
--- a/ghc/compiler/coreSyn/CoreUtils.lhs
+++ b/ghc/compiler/coreSyn/CoreUtils.lhs
@@ -46,7 +46,10 @@ import Var           ( Var )
 import VarSet          ( unionVarSet )
 import VarEnv
 import Name            ( hashName )
-import Packages                ( isDllName, HomeModules )
+import Packages                ( HomeModules )
+#if mingw32_TARGET_OS
+import Packages                ( isDllName )
+#endif
 import Literal         ( hashLiteral, literalType, litIsDupable, 
                          litIsTrivial, isZeroLit, Literal( MachLabel ) )
 import DataCon         ( DataCon, dataConRepArity, dataConArgTys,
@@ -66,7 +69,6 @@ import Type           ( Type, mkFunTy, mkForAllTy, splitFunTy_maybe,
                          splitTyConApp_maybe, coreEqType, funResultTy, applyTy
                        )
 import TyCon           ( tyConArity )
--- gaw 2004
 import TysWiredIn      ( boolTy, trueDataCon, falseDataCon )
 import CostCentre      ( CostCentre )
 import BasicTypes      ( Arity )
@@ -754,6 +756,27 @@ consider
 This should diverge!  But if we eta-expand, it won't.   Again, we ignore this
 "problem", because being scrupulous would lose an important transformation for
 many programs.
+
+
+4. Newtypes
+
+Non-recursive newtypes are transparent, and should not get in the way.
+We do (currently) eta-expand recursive newtypes too.  So if we have, say
+
+       newtype T = MkT ([T] -> Int)
+
+Suppose we have
+       e = coerce T f
+where f has arity 1.  Then: etaExpandArity e = 1; 
+that is, etaExpandArity looks through the coerce.
+
+When we eta-expand e to arity 1: eta_expand 1 e T
+we want to get:                 coerce T (\x::[T] -> (coerce ([T]->Int) e) x)
+
+HOWEVER, note that if you use coerce bogusly you can ge
+       coerce Int negate
+And since negate has arity 2, you might try to eta expand.  But you can't
+decopose Int to a function type.   Hence the final case in eta_expand.
 -}
 
 
@@ -946,7 +969,13 @@ eta_expand n us expr ty
 
        case splitRecNewType_maybe ty of {
          Just ty' -> mkCoerce2 ty ty' (eta_expand n us (mkCoerce2 ty' ty expr) ty') ;
-         Nothing  -> pprTrace "Bad eta expand" (ppr n $$ ppr expr $$ ppr ty) expr
+         Nothing  -> 
+
+       -- We have an expression of arity > 0, but its type isn't a function
+       -- This *can* legitmately happen: e.g.  coerce Int (\x. x)
+       -- Essentially the programmer is playing fast and loose with types
+       -- (Happy does this a lot).  So we simply decline to eta-expand.
+       expr
        }}}
 \end{code}
 

diff --git a/ghc/compiler/simplCore/Simplify.lhs b/ghc/compiler/simplCore/Simplify.lhs
index 610882d..d432024 100644 (file)
--- a/ghc/compiler/simplCore/Simplify.lhs
+++ b/ghc/compiler/simplCore/Simplify.lhs
@@ -40,7 +40,7 @@ import DataCon                ( dataConTyCon, dataConRepStrictness, isVanillaDataCon )
 import TyCon           ( tyConArity )
 import CoreSyn
 import PprCore         ( pprParendExpr, pprCoreExpr )
-import CoreUnfold      ( mkOtherCon, mkUnfolding, evaldUnfolding, callSiteInline )
+import CoreUnfold      ( mkUnfolding, callSiteInline )
 import CoreUtils       ( exprIsDupable, exprIsTrivial, needsCaseBinding,
                          exprIsConApp_maybe, mkPiTypes, findAlt, 
                          exprType, exprIsHNF, 
@@ -60,7 +60,6 @@ import BasicTypes     ( TopLevelFlag(..), isTopLevel,
                          RecFlag(..), isNonRec
                        )
 import OrdList
-import Maybe           ( Maybe )
 import Maybes          ( orElse )
 import Outputable
 import Util             ( notNull )
@@ -844,6 +843,11 @@ mkLamBndrZapper fun n_args
 \begin{code}
 simplNote env (Coerce to from) body cont
   = let
+       addCoerce s1 k1 cont    -- Drop redundant coerces.  This can happen if a polymoprhic
+                               -- (coerce a b e) is instantiated with a=ty1 b=ty2 and the
+                               -- two are the same. This happens a lot in Happy-generated parsers
+         | s1 `coreEqType` k1 = cont
+
        addCoerce s1 k1 (CoerceIt t1 cont)
                --      coerce T1 S1 (coerce S1 K1 e)
                -- ==>
@@ -854,9 +858,9 @@ simplNote env (Coerce to from) body cont
                -- we may find  (coerce T (coerce S (\x.e))) y
                -- and we'd like it to simplify to e[y/x] in one round 
                -- of simplification
-         | t1 `coreEqType` k1  = cont          -- The coerces cancel out
-         | otherwise       = CoerceIt t1 cont  -- They don't cancel, but 
-                                               -- the inner one is redundant
+         | t1 `coreEqType` k1  = cont                  -- The coerces cancel out
+         | otherwise           = CoerceIt t1 cont      -- They don't cancel, but 
+                                                       -- the inner one is redundant
 
        addCoerce t1t2 s1s2 (ApplyTo dup arg arg_se cont)
          | not (isTypeArg arg),        -- This whole case only works for value args