[project @ 2001-11-01 10:33:58 by simonpj]

----------------------------------
	Fix a bug in Simplify.mkDupableAlt
	----------------------------------

	[This is the HEAD commit; I've fixed
	 the branch separately.]

This fixes a funResultTy panic that Koen encountered.

The reason was that the simplifier was doing a
case-of-case where the result had a polymorphic type.
This in turn showed up because of a newtype (now
transparent) with a forall inside it.

The fix is very easy; can't think how I got it wrong
in the first place.

diff --git a/ghc/compiler/coreSyn/CoreUtils.lhs b/ghc/compiler/coreSyn/CoreUtils.lhs
index a1a4694..0877888 100644 (file)
--- a/ghc/compiler/coreSyn/CoreUtils.lhs
+++ b/ghc/compiler/coreSyn/CoreUtils.lhs
@@ -32,7 +32,7 @@ module CoreUtils (
        hashExpr,
 
        -- Equality
-       cheapEqExpr, eqExpr, applyTypeToArgs
+       cheapEqExpr, eqExpr, applyTypeToArgs, applyTypeToArg
     ) where
 
 #include "HsVersions.h"
@@ -59,7 +59,8 @@ import NewDemand      ( appIsBottom )
 import Type            ( Type, mkFunTy, mkForAllTy, splitFunTy_maybe, splitFunTy,
                          applyTys, isUnLiftedType, seqType, mkUTy, mkTyVarTy,
                          splitForAllTy_maybe, isForAllTy, splitNewType_maybe, 
-                         splitTyConApp_maybe, eqType, funResultTy, applyTy
+                         splitTyConApp_maybe, eqType, funResultTy, applyTy,
+                         funResultTy, applyTy
                        )
 import TyCon           ( tyConArity )
 import TysWiredIn      ( boolTy, trueDataCon, falseDataCon )
@@ -113,17 +114,24 @@ mkPiType v ty | isId v    = (case idLBVarInfo v of
 \end{code}
 
 \begin{code}
--- The first argument is just for debugging
+applyTypeToArg :: Type -> CoreExpr -> Type
+applyTypeToArg fun_ty (Type arg_ty) = applyTy fun_ty arg_ty
+applyTypeToArg fun_ty other_arg     = funResultTy fun_ty
+
 applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
+-- A more efficient version of applyTypeToArg 
+-- when we have several args
+-- The first argument is just for debugging
 applyTypeToArgs e op_ty [] = op_ty
 
 applyTypeToArgs e op_ty (Type ty : args)
   =    -- Accumulate type arguments so we can instantiate all at once
-    applyTypeToArgs e (applyTys op_ty tys) rest_args
+    go [ty] args
   where
-    (tys, rest_args)        = go [ty] args
-    go tys (Type ty : args) = go (ty:tys) args
-    go tys rest_args       = (reverse tys, rest_args)
+    go rev_tys (Type ty : args) = go (ty:rev_tys) args
+    go rev_tys rest_args        = applyTypeToArgs e op_ty' rest_args
+                               where
+                                 op_ty' = applyTys op_ty (reverse rev_tys)
 
 applyTypeToArgs e op_ty (other_arg : args)
   = case (splitFunTy_maybe op_ty) of

diff --git a/ghc/compiler/simplCore/Simplify.lhs b/ghc/compiler/simplCore/Simplify.lhs
index 33400a1..0d95dbe 100644 (file)
--- a/ghc/compiler/simplCore/Simplify.lhs
+++ b/ghc/compiler/simplCore/Simplify.lhs
@@ -40,7 +40,7 @@ import CoreUtils      ( exprIsDupable, exprIsTrivial, needsCaseBinding,
                          exprIsConApp_maybe, mkPiType, findAlt, 
                          exprType, coreAltsType, exprIsValue, 
                          exprOkForSpeculation, exprArity, findDefault,
-                         mkCoerce, mkSCC, mkInlineMe, mkAltExpr
+                         mkCoerce, mkSCC, mkInlineMe, mkAltExpr, applyTypeToArg
                        )
 import Rules           ( lookupRule )
 import BasicTypes      ( isMarkedStrict )
@@ -1552,10 +1552,14 @@ mkDupableCont env ty (ApplyTo _ arg se cont)
        --      ==>
        --              let a = ...arg... 
        --              in [...hole...] a
-    mkDupableCont env (funResultTy ty) cont            `thenSmpl` \ (floats, cont') ->
+    simplExpr (setInScope se env) arg                  `thenSmpl` \ arg' ->
+
+    mkDupableCont env (applyTypeToArg ty arg') cont    `thenSmpl` \ (floats, cont') ->
+       -- It's possible (albeit unusual) that arg is a type 
+       -- argument, if the alternatives have a for-all type; 
+       -- hence the applyTypeToArg
     addFloats env floats                               $ \ env ->
 
-    simplExpr (setInScope se env) arg                  `thenSmpl` \ arg' ->
     if exprIsDupable arg' then
        returnSmpl (emptyFloats env, ApplyTo OkToDup arg' (zapSubstEnv se) cont')
     else