X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2FcoreSyn%2FCoreUtils.lhs;h=4139a2a00b763c658e573c5d023e638ab3d46cc2;hp=103b294098e1ddca28abe5bf4529cf4d5e940dd0;hb=66413c79385a5b30a668e91789b8a334f6977ca9;hpb=afe4534704e8e0c25e2f90c6c0a2e397ecef24db diff --git a/compiler/coreSyn/CoreUtils.lhs b/compiler/coreSyn/CoreUtils.lhs index 103b294..4139a2a 100644 --- a/compiler/coreSyn/CoreUtils.lhs +++ b/compiler/coreSyn/CoreUtils.lhs @@ -55,7 +55,6 @@ import SrcLoc import VarEnv import VarSet import Name -import Module #if mingw32_TARGET_OS import Packages #endif @@ -1231,18 +1230,55 @@ There are some particularly delicate points here: These delicacies are why we don't use exprIsTrivial and exprIsHNF here. Alas. +Note [Eta reduction with casted arguments] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Consider + (\(x:t3). f (x |> g)) :: t3 -> t2 + where + f :: t1 -> t2 + g :: t3 ~ t1 +This should be eta-reduced to + + f |> (sym g -> t2) + +So we need to accumulate a coercion, pushing it inward (past +variable arguments only) thus: + f (x |> co_arg) |> co --> (f |> (sym co_arg -> co)) x + f (x:t) |> co --> (f |> (t -> co)) x + f @ a |> co --> (f |> (forall a.co)) @ a + f @ (g:t1~t2) |> co --> (f |> (t1~t2 => co)) @ (g:t1~t2) +These are the equations for ok_arg. + +It's true that we could also hope to eta reduce these: + (\xy. (f x |> g) y) + (\xy. (f x y) |> g) +But the simplifier pushes those casts outwards, so we don't +need to address that here. + \begin{code} tryEtaReduce :: [Var] -> CoreExpr -> Maybe CoreExpr tryEtaReduce bndrs body - = go (reverse bndrs) body + = go (reverse bndrs) body (IdCo (exprType body)) where incoming_arity = count isId bndrs - go (b : bs) (App fun arg) | ok_arg b arg = go bs fun -- Loop round - go [] fun | ok_fun fun = Just fun -- Success! - go _ _ = Nothing -- Failure! + go :: [Var] -- Binders, innermost first, types [a3,a2,a1] + -> CoreExpr -- Of type tr + -> CoercionI -- Of type tr ~ ts + -> Maybe CoreExpr -- Of type a1 -> a2 -> a3 -> ts + -- See Note [Eta reduction with casted arguments] + -- for why we have an accumulating coercion + go [] fun co + | ok_fun fun = Just (mkCoerceI co fun) + + go (b : bs) (App fun arg) co + | Just co' <- ok_arg b arg co + = go bs fun co' + + go _ _ _ = Nothing -- Failure! - -- Note [Eta reduction conditions] + --------------- + -- Note [Eta reduction conditions] ok_fun (App fun (Type ty)) | not (any (`elemVarSet` tyVarsOfType ty) bndrs) = ok_fun fun @@ -1251,17 +1287,37 @@ tryEtaReduce bndrs body && (ok_fun_id fun_id || all ok_lam bndrs) ok_fun _fun = False + --------------- ok_fun_id fun = fun_arity fun >= incoming_arity + --------------- fun_arity fun -- See Note [Arity care] | isLocalId fun && isLoopBreaker (idOccInfo fun) = 0 | otherwise = idArity fun + --------------- ok_lam v = isTyCoVar v || isDictId v - ok_arg b arg = varToCoreExpr b `cheapEqExpr` arg + --------------- + ok_arg :: Var -- Of type bndr_t + -> CoreExpr -- Of type arg_t + -> CoercionI -- Of kind (t1~t2) + -> Maybe CoercionI -- Of type (arg_t -> t1 ~ bndr_t -> t2) + -- (and similarly for tyvars, coercion args) + -- See Note [Eta reduction with casted arguments] + ok_arg bndr (Type ty) co + | Just tv <- getTyVar_maybe ty + , bndr == tv = Just (mkForAllTyCoI tv co) + ok_arg bndr (Var v) co + | bndr == v = Just (mkFunTyCoI (IdCo (idType bndr)) co) + ok_arg bndr (Cast (Var v) co_arg) co + | bndr == v = Just (mkFunTyCoI (ACo (mkSymCoercion co_arg)) co) + -- The simplifier combines multiple casts into one, + -- so we can have a simple-minded pattern match here + ok_arg _ _ _ = Nothing \end{code} + %************************************************************************ %* * \subsection{Determining non-updatable right-hand-sides} @@ -1280,7 +1336,7 @@ and 'execute' it rather than allocating it statically. -- | This function is called only on *top-level* right-hand sides. -- Returns @True@ if the RHS can be allocated statically in the output, -- with no thunks involved at all. -rhsIsStatic :: PackageId -> CoreExpr -> Bool +rhsIsStatic :: (Name -> Bool) -> CoreExpr -> Bool -- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or -- refers to, CAFs; (ii) in CoreToStg to decide whether to put an -- update flag on it and (iii) in DsExpr to decide how to expand @@ -1335,16 +1391,14 @@ rhsIsStatic :: PackageId -> CoreExpr -> Bool -- -- c) don't look through unfolding of f in (f x). -rhsIsStatic _this_pkg rhs = is_static False rhs +rhsIsStatic _is_dynamic_name rhs = is_static False rhs where is_static :: Bool -- True <=> in a constructor argument; must be atomic -> CoreExpr -> Bool - is_static False (Lam b e) = isRuntimeVar b || is_static False e - - is_static _ (Note (SCC _) _) = False - is_static in_arg (Note _ e) = is_static in_arg e - is_static in_arg (Cast e _) = is_static in_arg e + is_static False (Lam b e) = isRuntimeVar b || is_static False e + is_static in_arg (Note n e) = notSccNote n && is_static in_arg e + is_static in_arg (Cast e _) = is_static in_arg e is_static _ (Lit lit) = case lit of @@ -1363,7 +1417,7 @@ rhsIsStatic _this_pkg rhs = is_static False rhs where go (Var f) n_val_args #if mingw32_TARGET_OS - | not (isDllName _this_pkg (idName f)) + | not (_is_dynamic_name (idName f)) #endif = saturated_data_con f n_val_args || (in_arg && n_val_args == 0) @@ -1385,11 +1439,9 @@ rhsIsStatic _this_pkg rhs = is_static False rhs -- x = D# (1.0## /## 2.0##) -- can't float because /## can fail. - go (Note (SCC _) _) _ = False - go (Note _ f) n_val_args = go f n_val_args - go (Cast e _) n_val_args = go e n_val_args - - go _ _ = False + go (Note n f) n_val_args = notSccNote n && go f n_val_args + go (Cast e _) n_val_args = go e n_val_args + go _ _ = False saturated_data_con f n_val_args = case isDataConWorkId_maybe f of