where h :: Int -> Int# is expensive. We'd like to float the (h y) outside
the \x, but we don't because it's unboxed. Possible solution: box it.
+Note [Case MFEs]
+~~~~~~~~~~~~~~~~
+We don't float a case expression as an MFE from a strict context. Why not?
+Because in doing so we share a tiny bit of computation (the switch) but
+in exchange we build a thunk, which is bad. This case reduces allocation
+by 7% in spectral/puzzle (a rather strange benchmark) and 1.2% in real/fem.
+Doesn't change any other allocation at all.
+
\begin{code}
lvlMFE :: Bool -- True <=> strict context [body of case or let]
-> Level -- Level of innermost enclosing lambda/tylam
= do { expr' <- lvlMFE strict_ctxt ctxt_lvl env e
; return (Cast expr' co) }
+-- Note [Case MFEs]
+lvlMFE True ctxt_lvl env e@(_, AnnCase {})
+ = lvlExpr ctxt_lvl env e -- Don't share cases
+
lvlMFE strict_ctxt ctxt_lvl env ann_expr@(fvs, _)
| isUnLiftedType ty -- Can't let-bind it; see Note [Unlifted MFEs]
|| isInlineCtxt ctxt_lvl -- Don't float out of an __inline__ context
let new_bndrs = zipWith mk_poly_bndr bndrs uniqs
return (extendPolyLvlEnv dest_lvl env abs_vars (bndrs `zip` new_bndrs), new_bndrs)
where
- mk_poly_bndr bndr uniq = transferPolyIdInfo bndr $ -- Note [transferPolyIdInfo] in Id.lhs
+ mk_poly_bndr bndr uniq = transferPolyIdInfo bndr abs_vars $ -- Note [transferPolyIdInfo] in Id.lhs
mkSysLocal (mkFastString str) uniq poly_ty
where
str = "poly_" ++ occNameString (getOccName bndr)