[project @ 2005-03-24 15:11:07 by simonmar]

mkStgAltType: try to find the non-abstract TyCon if the one in the
type of the case binder turns out to be an HiBootTyCon.  Fixes
possible code generation bugs when compiling programs with recursive
modules.

diff --git a/ghc/compiler/stgSyn/CoreToStg.lhs b/ghc/compiler/stgSyn/CoreToStg.lhs
index 8a97d51..734e5fd 100644 (file)
--- a/ghc/compiler/stgSyn/CoreToStg.lhs
+++ b/ghc/compiler/stgSyn/CoreToStg.lhs
@@ -12,7 +12,7 @@ module CoreToStg ( coreToStg, coreExprToStg ) where
 #include "HsVersions.h"
 
 import CoreSyn
-import CoreUtils       ( rhsIsStatic, manifestArity, exprType )
+import CoreUtils       ( rhsIsStatic, manifestArity, exprType, findDefault )
 import StgSyn
 
 import Type
@@ -371,7 +371,7 @@ coreToStgExpr (Case scrut bndr _ alts)
                     (getLiveVars alts_lv_info)
                     bndr'
                     (mkSRT alts_lv_info)
-                    (mkStgAltType (idType bndr)) 
+                    (mkStgAltType (idType bndr) alts)
                     alts2,
       scrut_fvs `unionFVInfo` alts_fvs_wo_bndr,
       alts_escs_wo_bndr `unionVarSet` getFVSet scrut_fvs
@@ -411,15 +411,29 @@ coreToStgExpr (Let bind body)
 \end{code}
 
 \begin{code}
-mkStgAltType scrut_ty
+mkStgAltType scrut_ty alts
   = case splitTyConApp_maybe (repType scrut_ty) of
        Just (tc,_) | isUnboxedTupleTyCon tc -> UbxTupAlt tc
                    | isPrimTyCon tc         -> PrimAlt tc
-                   | isHiBootTyCon tc       -> PolyAlt -- Algebraic, but no constructors visible
+                   | isHiBootTyCon tc       -> look_for_better_tycon
                    | isAlgTyCon tc          -> AlgAlt tc
                    | isFunTyCon tc          -> PolyAlt
                    | otherwise              -> pprPanic "mkStgAlts" (ppr tc)
        Nothing                              -> PolyAlt
+
+  where
+   -- Sometimes, the TyCon in the type of the scrutinee is an HiBootTyCon,
+   -- which may not have any constructors inside it.  If so, then we
+   -- can get a better TyCon by grabbing the one from a constructor alternative
+   -- if one exists.
+   look_for_better_tycon
+       | ((DataAlt con, _, _) : _) <- data_alts = 
+               AlgAlt (dataConTyCon con)
+       | otherwise =
+               ASSERT(null data_alts)
+               PolyAlt
+       where
+               (data_alts, deflt) = findDefault alts
 \end{code}