Record evaluated-ness information correctly for strict constructors

[ghc-hetmet.git] / compiler / simplCore / Simplify.lhs

diff --git a/compiler/simplCore/Simplify.lhs b/compiler/simplCore/Simplify.lhs
index 9723dfb..baf2a30 100644 (file)
--- a/compiler/simplCore/Simplify.lhs
+++ b/compiler/simplCore/Simplify.lhs
@@ -1572,19 +1572,19 @@ simplAlt env imposs_deflt_cons case_bndr' cont' (LitAlt lit, bndrs, rhs)
 
 simplAlt env imposs_deflt_cons case_bndr' cont' (DataAlt con, vs, rhs)
   = do {       -- Deal with the pattern-bound variables
-         (env, vs') <- simplBinders env (add_evals con vs)
-
                -- Mark the ones that are in ! positions in the
                -- data constructor as certainly-evaluated.
-       ; let vs'' = add_evals con vs'
+               -- NB: simplLamBinders preserves this eval info
+         let vs_with_evals = add_evals vs (dataConRepStrictness con)
+       ; (env, vs') <- simplLamBndrs env vs_with_evals
 
                -- Bind the case-binder to (con args)
        ; let inst_tys' = tyConAppArgs (idType case_bndr')
-             con_args  = map Type inst_tys' ++ varsToCoreExprs vs'' 
+             con_args  = map Type inst_tys' ++ varsToCoreExprs vs' 
              env'      = addBinderUnfolding env case_bndr' (mkConApp con con_args)
 
        ; rhs' <- simplExprC env' rhs cont'
-       ; return (DataAlt con, vs'', rhs') }
+       ; return (DataAlt con, vs', rhs') }
   where
        -- add_evals records the evaluated-ness of the bound variables of
        -- a case pattern.  This is *important*.  Consider
@@ -1595,9 +1595,7 @@ simplAlt env imposs_deflt_cons case_bndr' cont' (DataAlt con, vs, rhs)
        -- We really must record that b is already evaluated so that we don't
        -- go and re-evaluate it when constructing the result.
        -- See Note [Data-con worker strictness] in MkId.lhs
-    add_evals dc vs = cat_evals dc vs (dataConRepStrictness dc)
-
-    cat_evals dc vs strs
+    add_evals vs strs
        = go vs strs
        where
          go [] [] = []
@@ -1608,12 +1606,15 @@ simplAlt env imposs_deflt_cons case_bndr' cont' (DataAlt con, vs, rhs)
            where
              zapped_v = zap_occ_info v
              evald_v  = zapped_v `setIdUnfolding` evaldUnfolding
-         go _ _ = pprPanic "cat_evals" (ppr dc $$ ppr vs $$ ppr strs)
+         go _ _ = pprPanic "cat_evals" (ppr con $$ ppr vs $$ ppr strs)
 
-       -- If the case binder is alive, then we add the unfolding
+       -- zap_occ_info: if the case binder is alive, then we add the unfolding
        --      case_bndr = C vs
        -- to the envt; so vs are now very much alive
-       -- Note [Aug06] I can't see why this actually matters
+       -- Note [Aug06] I can't see why this actually matters, but it's neater
+       --        case e of t { (a,b) -> ...(case t of (p,q) -> p)... }
+       --   ==>  case e of t { (a,b) -> ...(a)... }
+       -- Look, Ma, a is alive now.
     zap_occ_info | isDeadBinder case_bndr' = \id -> id
                 | otherwise               = zapOccInfo