import MonadUtils
import Control.Monad
-import Data.List
\end{code}
%************************************************************************
; sel_binds <- mkSelectorBinds pat body_expr
; return (sel_binds ++ rest) }
-{- Note [Rules and inlining]
- ~~~~~~~~~~~~~~~~~~~~~~~~~
- Common special case: no type or dictionary abstraction
- This is a bit less trivial than you might suppose
- The naive way woudl be to desguar to something like
- f_lcl = ...f_lcl... -- The "binds" from AbsBinds
- M.f = f_lcl -- Generated from "exports"
- But we don't want that, because if M.f isn't exported,
- it'll be inlined unconditionally at every call site (its rhs is
- trivial). That would be ok unless it has RULES, which would
- thereby be completely lost. Bad, bad, bad.
-
- Instead we want to generate
- M.f = ...f_lcl...
- f_lcl = M.f
- Now all is cool. The RULES are attached to M.f (by SimplCore),
- and f_lcl is rapidly inlined away.
-
- This does not happen in the same way to polymorphic binds,
- because they desugar to
- M.f = /\a. let f_lcl = ...f_lcl... in f_lcl
- Although I'm a bit worried about whether full laziness might
- float the f_lcl binding out and then inline M.f at its call site -}
-
dsHsBind auto_scc rest (AbsBinds [] [] exports binds)
= do { core_prs <- ds_lhs_binds NoSccs binds
; let env = mkABEnv exports
do_one (lcl_id, rhs)
| Just (_, gbl_id, _, spec_prags) <- lookupVarEnv env lcl_id
- = WARN( hasSpecPrags spec_prags, pprTcSpecPrags gbl_id spec_prags ) -- Not overloaded
- makeCorePair gbl_id False 0 (addAutoScc auto_scc gbl_id rhs)
+ = do { let rhs' = addAutoScc auto_scc gbl_id rhs
+ ; (spec_binds, rules) <- dsSpecs gbl_id (Let (Rec core_prs) rhs') spec_prags
+ -- See Note [Specialising in no-dict case]
+ ; let gbl_id' = addIdSpecialisations gbl_id rules
+ main_bind = makeCorePair gbl_id' False 0 rhs'
+ ; return (main_bind : spec_binds) }
- | otherwise = (lcl_id, rhs)
+ | otherwise = return [(lcl_id, rhs)]
locals' = [(lcl_id, Var gbl_id) | (_, gbl_id, lcl_id, _) <- exports]
-- Note [Rules and inlining]
- ; return (map do_one core_prs ++ locals' ++ rest) }
+ ; export_binds <- mapM do_one core_prs
+ ; return (concat export_binds ++ locals' ++ rest) }
-- No Rec needed here (contrast the other AbsBinds cases)
-- because we can rely on the enclosing dsBind to wrap in Rec
-{- Note [Abstracting over tyvars only]
- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- When abstracting over type variable only (not dictionaries), we don't really need to
- built a tuple and select from it, as we do in the general case. Instead we can take
-
- AbsBinds [a,b] [ ([a,b], fg, fl, _),
- ([b], gg, gl, _) ]
- { fl = e1
- gl = e2
- h = e3 }
-
- and desugar it to
-
- fg = /\ab. let B in e1
- gg = /\b. let a = () in let B in S(e2)
- h = /\ab. let B in e3
-
- where B is the *non-recursive* binding
- fl = fg a b
- gl = gg b
- h = h a b -- See (b); note shadowing!
-
- Notice (a) g has a different number of type variables to f, so we must
- use the mkArbitraryType thing to fill in the gaps.
- We use a type-let to do that.
-
- (b) The local variable h isn't in the exports, and rather than
- clone a fresh copy we simply replace h by (h a b), where
- the two h's have different types! Shadowing happens here,
- which looks confusing but works fine.
-
- (c) The result is *still* quadratic-sized if there are a lot of
- small bindings. So if there are more than some small
- number (10), we filter the binding set B by the free
- variables of the particular RHS. Tiresome.
-
- Why got to this trouble? It's a common case, and it removes the
- quadratic-sized tuple desugaring. Less clutter, hopefullly faster
- compilation, especially in a case where there are a *lot* of
- bindings.
--}
-
-
dsHsBind auto_scc rest (AbsBinds tyvars [] exports binds)
| opt_DsMultiTyVar -- This (static) debug flag just lets us
-- switch on and off this optimisation to
do_one lg_binds (lcl_id, rhs)
| Just (id_tvs, gbl_id, _, spec_prags) <- lookupVarEnv env lcl_id
- = WARN( hasSpecPrags spec_prags, pprTcSpecPrags gbl_id spec_prags ) -- Not overloaded
- (let rhs' = addAutoScc auto_scc gbl_id $
- mkLams id_tvs $
- mkLets [ NonRec tv (Type (lookupVarEnv_NF arby_env tv))
- | tv <- tyvars, not (tv `elem` id_tvs)] $
- add_lets lg_binds rhs
- in return (mk_lg_bind lcl_id gbl_id id_tvs,
- makeCorePair gbl_id False 0 rhs'))
+ = do { let rhs' = addAutoScc auto_scc gbl_id $
+ mkLams id_tvs $
+ mkLets [ NonRec tv (Type (lookupVarEnv_NF arby_env tv))
+ | tv <- tyvars, not (tv `elem` id_tvs)] $
+ add_lets lg_binds rhs
+ ; (spec_binds, rules) <- dsSpecs gbl_id rhs' spec_prags
+ ; let gbl_id' = addIdSpecialisations gbl_id rules
+ main_bind = makeCorePair gbl_id' False 0 rhs'
+ ; return (mk_lg_bind lcl_id gbl_id' id_tvs, main_bind : spec_binds) }
| otherwise
= do { non_exp_gbl_id <- newUniqueId lcl_id (mkForAllTys tyvars (idType lcl_id))
; return (mk_lg_bind lcl_id non_exp_gbl_id tyvars,
- (non_exp_gbl_id, mkLams tyvars (add_lets lg_binds rhs))) }
+ [(non_exp_gbl_id, mkLams tyvars (add_lets lg_binds rhs))]) }
; (_, core_prs') <- fixDs (\ ~(lg_binds, _) -> mapAndUnzipM (do_one lg_binds) core_prs)
- ; return (core_prs' ++ rest) }
+ ; return (concat core_prs' ++ rest) }
-- Another common case: one exported variable
-- Non-recursive bindings come through this way
; let -- Always treat the binds as recursive, because the
-- typechecker makes rather mixed-up dictionary bindings
core_bind = Rec core_prs
+ rhs = addAutoScc auto_scc global $
+ mkLams tyvars $ mkLams dicts $ Let core_bind (Var local)
- ; (spec_binds, rules) <- dsSpecs all_tyvars dicts tyvars global
- local core_bind prags
+ ; (spec_binds, rules) <- dsSpecs global rhs prags
; let global' = addIdSpecialisations global rules
- rhs = addAutoScc auto_scc global $
- mkLams tyvars $ mkLams dicts $ Let core_bind (Var local)
main_bind = makeCorePair global' (isDefaultMethod prags)
(dictArity dicts) rhs
-- Rec because of mixed-up dictionary bindings
core_bind = Rec (map do_one core_prs)
- tup_expr = mkBigCoreVarTup locals
- tup_ty = exprType tup_expr
- poly_tup_expr = mkLams all_tyvars $ mkLams dicts $
- Let core_bind tup_expr
- locals = [local | (_, _, local, _) <- exports]
- local_tys = map idType locals
+ tup_expr = mkBigCoreVarTup locals
+ tup_ty = exprType tup_expr
+ poly_tup_rhs = mkLams all_tyvars $ mkLams dicts $
+ Let core_bind tup_expr
+ locals = [local | (_, _, local, _) <- exports]
+ local_tys = map idType locals
- ; poly_tup_id <- newSysLocalDs (exprType poly_tup_expr)
+ ; poly_tup_id <- newSysLocalDs (exprType poly_tup_rhs)
- ; let mk_bind ((tyvars, global, local, spec_prags), n) -- locals!!n == local
+ ; let mk_bind ((tyvars, global, _, spec_prags), n) -- locals!!n == local
= -- Need to make fresh locals to bind in the selector,
-- because some of the tyvars will be bound to 'Any'
do { let ty_args = map mk_ty_arg all_tyvars
substitute = substTyWith all_tyvars ty_args
; locals' <- newSysLocalsDs (map substitute local_tys)
; tup_id <- newSysLocalDs (substitute tup_ty)
- ; (spec_binds, rules) <- dsSpecs all_tyvars dicts tyvars global local
- core_bind
- spec_prags
- ; let global' = addIdSpecialisations global rules
- rhs = mkLams tyvars $ mkLams dicts $
+ ; let rhs = mkLams tyvars $ mkLams dicts $
mkTupleSelector locals' (locals' !! n) tup_id $
mkVarApps (mkTyApps (Var poly_tup_id) ty_args)
dicts
+ ; (spec_binds, rules) <- dsSpecs global
+ (Let (NonRec poly_tup_id poly_tup_rhs) rhs)
+ spec_prags
+ ; let global' = addIdSpecialisations global rules
; return ((global', rhs) : spec_binds) }
where
mk_ty_arg all_tyvar
; export_binds_s <- mapM mk_bind (exports `zip` [0..])
-- Don't scc (auto-)annotate the tuple itself.
- ; return ((poly_tup_id, poly_tup_expr) :
+ ; return ((poly_tup_id, poly_tup_rhs) :
(concat export_binds_s ++ rest)) }
------------------------
mkABEnv exports = mkVarEnv [ (lcl_id, export) | export@(_, _, lcl_id, _) <- exports]
\end{code}
+Note [Rules and inlining]
+~~~~~~~~~~~~~~~~~~~~~~~~~
+Common special case: no type or dictionary abstraction
+This is a bit less trivial than you might suppose
+The naive way woudl be to desguar to something like
+ f_lcl = ...f_lcl... -- The "binds" from AbsBinds
+ M.f = f_lcl -- Generated from "exports"
+But we don't want that, because if M.f isn't exported,
+it'll be inlined unconditionally at every call site (its rhs is
+trivial). That would be ok unless it has RULES, which would
+thereby be completely lost. Bad, bad, bad.
+
+Instead we want to generate
+ M.f = ...f_lcl...
+ f_lcl = M.f
+Now all is cool. The RULES are attached to M.f (by SimplCore),
+and f_lcl is rapidly inlined away.
+
+This does not happen in the same way to polymorphic binds,
+because they desugar to
+ M.f = /\a. let f_lcl = ...f_lcl... in f_lcl
+Although I'm a bit worried about whether full laziness might
+float the f_lcl binding out and then inline M.f at its call site -}
+
+Note [Specialising in no-dict case]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Even if there are no tyvars or dicts, we may have specialisation pragmas.
+Class methods can generate
+ AbsBinds [] [] [( ... spec-prag]
+ { AbsBinds [tvs] [dicts] ...blah }
+So the overloading is in the nested AbsBinds. A good example is in GHC.Float:
+
+ class (Real a, Fractional a) => RealFrac a where
+ round :: (Integral b) => a -> b
+
+ instance RealFrac Float where
+ {-# SPECIALIZE round :: Float -> Int #-}
+
+The top-level AbsBinds for $cround has no tyvars or dicts (because the
+instance does not). But the method is locally overloaded!
+
+Note [Abstracting over tyvars only]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+When abstracting over type variable only (not dictionaries), we don't really need to
+built a tuple and select from it, as we do in the general case. Instead we can take
+
+ AbsBinds [a,b] [ ([a,b], fg, fl, _),
+ ([b], gg, gl, _) ]
+ { fl = e1
+ gl = e2
+ h = e3 }
+
+and desugar it to
+
+ fg = /\ab. let B in e1
+ gg = /\b. let a = () in let B in S(e2)
+ h = /\ab. let B in e3
+
+where B is the *non-recursive* binding
+ fl = fg a b
+ gl = gg b
+ h = h a b -- See (b); note shadowing!
+
+Notice (a) g has a different number of type variables to f, so we must
+ use the mkArbitraryType thing to fill in the gaps.
+ We use a type-let to do that.
+
+ (b) The local variable h isn't in the exports, and rather than
+ clone a fresh copy we simply replace h by (h a b), where
+ the two h's have different types! Shadowing happens here,
+ which looks confusing but works fine.
+
+ (c) The result is *still* quadratic-sized if there are a lot of
+ small bindings. So if there are more than some small
+ number (10), we filter the binding set B by the free
+ variables of the particular RHS. Tiresome.
+
+Why got to this trouble? It's a common case, and it removes the
+quadratic-sized tuple desugaring. Less clutter, hopefullly faster
+compilation, especially in a case where there are a *lot* of
+bindings.
+
+
Note [Eta-expanding INLINE things]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider
Example:
f :: (Eq a, Ix b) => a -> b -> Bool
{-# SPECIALISE f :: (Ix p, Ix q) => Int -> (p,q) -> Bool #-}
+ f = <poly_rhs>
From this the typechecker generates
-> forall p q. (Ix p, Ix q) => XXX[ Int/a, (p,q)/b ])
Note that wrap_fn can transform *any* function with the right type prefix
- forall ab. (Eq a, Ix b) => <blah>
-regardless of <blah>. It's sort of polymorphic in <blah>. This is
+ forall ab. (Eq a, Ix b) => XXX
+regardless of XXX. It's sort of polymorphic in XXX. This is
useful: we use the same wrapper to transform each of the class ops, as
well as the dict.
Rule: forall p, q, (dp:Ix p), (dq:Ix q).
f Int (p,q) dInt ($dfInPair dp dq) = f_spec p q dp dq
- Spec bind: f_spec = wrap_fn (/\ab \d1 d2. Let binds in f_mono)
+ Spec bind: f_spec = wrap_fn <poly_rhs>
Note that
$dfIxPair dp dq), and that is essential because the dp, dq are
needed on the RHS.
- * The RHS of f_spec has a *copy* of 'binds', so that it can fully
- specialise it.
+ * The RHS of f_spec, <poly_rhs> has a *copy* of 'binds', so that it
+ can fully specialise it.
\begin{code}
------------------------
-dsSpecs :: [TyVar] -> [DictId] -> [TyVar]
- -> Id -> Id -- Global, local
- -> CoreBind -> TcSpecPrags
+dsSpecs :: Id -- The polymorphic Id
+ -> CoreExpr -- Its rhs
+ -> TcSpecPrags
-> DsM ( [(Id,CoreExpr)] -- Binding for specialised Ids
, [CoreRule] ) -- Rules for the Global Ids
-- See Note [Implementing SPECIALISE pragmas]
-dsSpecs all_tvs dicts tvs poly_id mono_id mono_bind prags
+dsSpecs poly_id poly_rhs prags
= case prags of
IsDefaultMethod -> return ([], [])
SpecPrags sps -> do { pairs <- mapMaybeM spec_one sps
{ (spec_unf, unf_pairs) <- specUnfolding wrap_fn (realIdUnfolding poly_id)
- ; let f_body = fix_up (Let mono_bind (Var mono_id))
- spec_ty = exprType ds_spec_expr
+ ; let spec_ty = exprType ds_spec_expr
spec_id = mkLocalId spec_name spec_ty
`setInlinePragma` inl_prag
`setIdUnfolding` spec_unf
(extra_dict_bndrs ++ bndrs) args
(mkVarApps (Var spec_id) bndrs)
- spec_rhs = wrap_fn (mkLams (tvs ++ dicts) f_body)
+ spec_rhs = wrap_fn poly_rhs
spec_pair = makeCorePair spec_id False (dictArity bndrs) spec_rhs
; return (Just (spec_pair : unf_pairs, rule))
} } } }
- -- Bind to Any any of all_ptvs that aren't
- -- relevant for this particular function
- fix_up body | null void_tvs = body
- | otherwise = mkTyApps (mkLams void_tvs body) $
- map dsMkArbitraryType void_tvs
-
- void_tvs = all_tvs \\ tvs
-
dead_msg bs = vcat [ sep [ptext (sLit "Useless constraint") <> plural bs
<+> ptext (sLit "in specialied type:"),
nest 2 (pprTheta (map get_pred bs))]
projects / ghc-hetmet.git / commitdiff