[project @ 2001-10-18 16:11:57 by simonpj]

Correct bug in todays bug-fix to DmdAnal

diff --git a/ghc/compiler/stranal/DmdAnal.lhs b/ghc/compiler/stranal/DmdAnal.lhs
index 82106c2..17775e7 100644 (file)
--- a/ghc/compiler/stranal/DmdAnal.lhs
+++ b/ghc/compiler/stranal/DmdAnal.lhs
@@ -589,18 +589,25 @@ dmdTransform sigs var dmd
 
 ------         DATA CONSTRUCTOR
   | isDataConId var,           -- Data constructor
-    Seq k ds <- res_dmd,       -- and the demand looks inside its fields
-    let StrictSig dmd_ty = idNewStrictness var,        -- It must have a strictness sig
-    let DmdType _ _ con_res = dmd_ty
-  = if idArity var == call_depth then          -- Saturated, so unleash the demand
-       -- ds can be empty, when we are just seq'ing the thing
+    Seq k ds <- res_dmd                -- and the demand looks inside its fields
+  = let 
+       StrictSig dmd_ty    = idNewStrictness var       -- It must have a strictness sig
+       DmdType _ _ con_res = dmd_ty
+       arity               = idArity var
+    in
+    if arity == call_depth then                -- Saturated, so unleash the demand
        let 
+               -- ds can be empty, when we are just seq'ing the thing
+               -- If so we must make up a suitable bunch of demands
+          dmd_ds | null ds   = replicate arity Abs
+                 | otherwise = ASSERT( length ds == arity ) ds
+
           arg_ds = case k of
-                       Keep  -> bothLazy_s ds
-                       Drop  -> ds
+                       Keep  -> bothLazy_s dmd_ds
+                       Drop  -> dmd_ds
                        Defer -> pprTrace "dmdTransform: surprising!" (ppr var) 
                                        -- I don't think this can happen
-                                ds
+                                dmd_ds
                -- Important!  If we Keep the constructor application, then
                -- we need the demands the constructor places (always lazy)
                -- If not, we don't need to.  For example: