Fix cardinality change of fields in addDataConStrictness

Test Plan: This validates

Reviewers: simonpj, bgamari

Reviewed By: bgamari

Subscribers: rwbarton, carter

Differential Revision: https://phabricator.haskell.org/D5225

compiler/basicTypes/Demand.hs

@@ -56,7 +56,7 @@ module Demand (
         useCount, isUsedOnce, reuseEnv,
         killUsageDemand, killUsageSig, zapUsageDemand, zapUsageEnvSig,
         zapUsedOnceDemand, zapUsedOnceSig,
-        strictifyDictDmd
+        strictifyDictDmd, strictifyDmd
 
      ) where
 
@@ -2033,6 +2033,10 @@ strictifyDictDmd ty dmd = case getUseDmd dmd of
              -- the superclass dicts are always a prefix
   _ -> dmd -- unused or not a dictionary
 
+strictifyDmd :: Demand -> Demand
+strictifyDmd dmd@(JD { sd = str })
+  = dmd { sd = str `bothArgStr` Str VanStr HeadStr }
+
 {-
 Note [HyperStr and Use demands]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

compiler/stranal/DmdAnal.hs

@@ -1222,7 +1222,7 @@ addDataConStrictness con ds
   where
     strs = dataConRepStrictness con
     add dmd str | isMarkedStrict str
-                , not (isAbsDmd dmd) = dmd `bothDmd` seqDmd
+                , not (isAbsDmd dmd) = strictifyDmd dmd
                 | otherwise          = dmd
 
 findBndrsDmds :: AnalEnv -> DmdType -> [Var] -> (DmdType, [Demand])