\begin{code}
module DsBinds ( dsTopLHsBinds, dsLHsBinds, decomposeRuleLhs,
- dsCoercion,
- AutoScc(..)
+ dsHsWrapper, dsTcEvBinds, dsEvBinds, wrapDsEvBinds,
+ DsEvBind(..), AutoScc(..)
) where
#include "HsVersions.h"
import CoreSubst
import MkCore
import CoreUtils
+import CoreArity ( etaExpand )
import CoreUnfold
import CoreFVs
+import Digraph
import TcType
+import Type
import TysPrim ( anyTypeOfKind )
import CostCentre
import Module
import Id
+import TyCon ( tyConDataCons )
+import Class
+import DataCon ( dataConRepType )
+import Name ( localiseName )
import MkId ( seqId )
-import Var ( Var, TyVar, tyVarKind )
-import IdInfo ( vanillaIdInfo )
+import Var
import VarSet
import Rules
import VarEnv
import Outputable
import SrcLoc
import Maybes
+import OrdList
import Bag
import BasicTypes hiding ( TopLevel )
import FastString
-import StaticFlags ( opt_DsMultiTyVar )
-import Util ( count, lengthExceeds )
+-- import StaticFlags ( opt_DsMultiTyVar )
+import Util
import MonadUtils
-import Control.Monad
-import Data.List
\end{code}
%************************************************************************
\begin{code}
dsTopLHsBinds :: AutoScc -> LHsBinds Id -> DsM [(Id,CoreExpr)]
-dsTopLHsBinds auto_scc binds = ds_lhs_binds auto_scc binds
+dsTopLHsBinds auto_scc binds = do { binds' <- ds_lhs_binds auto_scc binds
+ ; return (fromOL binds') }
dsLHsBinds :: LHsBinds Id -> DsM [(Id,CoreExpr)]
-dsLHsBinds binds = ds_lhs_binds NoSccs binds
-
+dsLHsBinds binds = do { binds' <- ds_lhs_binds NoSccs binds
+ ; return (fromOL binds') }
------------------------
-ds_lhs_binds :: AutoScc -> LHsBinds Id -> DsM [(Id,CoreExpr)]
+ds_lhs_binds :: AutoScc -> LHsBinds Id -> DsM (OrdList (Id,CoreExpr))
-- scc annotation policy (see below)
-ds_lhs_binds auto_scc binds = foldM (dsLHsBind auto_scc) [] (bagToList binds)
+ds_lhs_binds auto_scc binds = do { ds_bs <- mapBagM (dsLHsBind auto_scc) binds
+ ; return (foldBag appOL id nilOL ds_bs) }
-dsLHsBind :: AutoScc
- -> [(Id,CoreExpr)] -- Put this on the end (avoid quadratic append)
- -> LHsBind Id
- -> DsM [(Id,CoreExpr)] -- Result
-dsLHsBind auto_scc rest (L loc bind)
- = putSrcSpanDs loc $ dsHsBind auto_scc rest bind
+dsLHsBind :: AutoScc -> LHsBind Id -> DsM (OrdList (Id,CoreExpr))
+dsLHsBind auto_scc (L loc bind)
+ = putSrcSpanDs loc $ dsHsBind auto_scc bind
-dsHsBind :: AutoScc
- -> [(Id,CoreExpr)] -- Put this on the end (avoid quadratic append)
- -> HsBind Id
- -> DsM [(Id,CoreExpr)] -- Result
+dsHsBind :: AutoScc -> HsBind Id -> DsM (OrdList (Id,CoreExpr))
-dsHsBind _ rest (VarBind { var_id = var, var_rhs = expr, var_inline = inline_regardless })
+dsHsBind _ (VarBind { var_id = var, var_rhs = expr, var_inline = inline_regardless })
= do { core_expr <- dsLExpr expr
-- Dictionary bindings are always VarBinds,
; let var' | inline_regardless = var `setIdUnfolding` mkCompulsoryUnfolding core_expr'
| otherwise = var
- ; return ((var', core_expr') : rest) }
+ ; return (unitOL (var', core_expr')) }
-dsHsBind _ rest
- (FunBind { fun_id = L _ fun, fun_matches = matches,
- fun_co_fn = co_fn, fun_tick = tick, fun_infix = inf })
+dsHsBind _ (FunBind { fun_id = L _ fun, fun_matches = matches
+ , fun_co_fn = co_fn, fun_tick = tick
+ , fun_infix = inf })
= do { (args, body) <- matchWrapper (FunRhs (idName fun) inf) matches
; body' <- mkOptTickBox tick body
- ; wrap_fn' <- dsCoercion co_fn
- ; return ((fun, wrap_fn' (mkLams args body')) : rest) }
+ ; wrap_fn' <- dsHsWrapper co_fn
+ ; return (unitOL (fun, wrap_fn' (mkLams args body'))) }
-dsHsBind _ rest
- (PatBind { pat_lhs = pat, pat_rhs = grhss, pat_rhs_ty = ty })
+dsHsBind _ (PatBind { pat_lhs = pat, pat_rhs = grhss, pat_rhs_ty = ty })
= do { body_expr <- dsGuarded grhss ty
; 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
- ar_env = mkArityEnv binds
+ ; return (toOL sel_binds) }
+
+{-
+dsHsBind auto_scc (AbsBinds { abs_tvs = [], abs_ev_vars = []
+ , abs_exports = exports, abs_ev_binds = ev_binds
+ , abs_binds = binds })
+ = do { bind_prs <- ds_lhs_binds NoSccs binds
+ ; ds_ev_binds <- dsTcEvBinds ev_binds
+
+ ; let core_prs = addEvPairs ds_ev_binds bind_prs
+ env = mkABEnv exports
do_one (lcl_id, rhs)
| Just (_, gbl_id, _, spec_prags) <- lookupVarEnv env lcl_id
- = ASSERT( null spec_prags ) -- Not overloaded
- makeCorePair gbl_id (lookupArity ar_env lcl_id) $
- 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)
+dsHsBind auto_scc rest (AbsBinds { abs_tvs = tyvars, abs_ev_vars = []
+ , abs_exports = exports, abs_ev_binds = ev_binds
+ , abs_binds = binds })
| opt_DsMultiTyVar -- This (static) debug flag just lets us
-- switch on and off this optimisation to
-- see if it has any impact; it is on by default
+ , allOL isLazyEvBind ev_binds
= -- Note [Abstracting over tyvars only]
- do { core_prs <- ds_lhs_binds NoSccs binds
- ; let arby_env = mkArbitraryTypeEnv tyvars exports
+ do { bind_prs <- ds_lhs_binds NoSccs binds
+ ; ds_ev_binds <- dsTcEvBinds ev_binds
+
+ ; let core_prs = addEvPairs ds_ev_binds bind_prs
+ arby_env = mkArbitraryTypeEnv tyvars exports
bndrs = mkVarSet (map fst core_prs)
add_lets | core_prs `lengthExceeds` 10 = add_some
where
fvs = exprSomeFreeVars (`elemVarSet` bndrs) rhs
- ar_env = mkArityEnv binds
env = mkABEnv exports
-
mk_lg_bind lcl_id gbl_id tyvars
= NonRec (setIdInfo lcl_id vanillaIdInfo)
-- Nuke the IdInfo so that no old unfoldings
do_one lg_binds (lcl_id, rhs)
| Just (id_tvs, gbl_id, _, spec_prags) <- lookupVarEnv env lcl_id
- = ASSERT( null 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 (lookupArity ar_env lcl_id) 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
+ -- A common case: one exported variable
-- Non-recursive bindings come through this way
-- So do self-recursive bindings, and recursive bindings
-- that have been chopped up with type signatures
-dsHsBind auto_scc rest
- (AbsBinds all_tyvars dicts [(tyvars, global, local, prags)] binds)
+dsHsBind auto_scc (AbsBinds { abs_tvs = all_tyvars, abs_ev_vars = dicts
+ , abs_exports = [(tyvars, global, local, prags)]
+ , abs_ev_binds = ev_binds, abs_binds = binds })
= ASSERT( all (`elem` tyvars) all_tyvars )
- do { core_prs <- ds_lhs_binds NoSccs binds
+ do { bind_prs <- ds_lhs_binds NoSccs binds
+ ; ds_ev_binds <- dsTcEvBinds ev_binds
- ; let -- Always treat the binds as recursive, because the typechecker
- -- makes rather mixed-up dictionary bindings
- core_bind = Rec core_prs
- inl_arity = lookupArity (mkArityEnv binds) local
+ ; let core_bind = Rec (fromOL bind_prs)
+ rhs = addAutoScc auto_scc global $
+ mkLams tyvars $ mkLams dicts $
+ wrapDsEvBinds ds_ev_binds $
+ Let core_bind $
+ Var local
- ; (spec_binds, rules) <- dsSpecs all_tyvars dicts tyvars global
- local inl_arity 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' (inl_arity + dictArity dicts) rhs
+ main_bind = makeCorePair global' (isDefaultMethod prags)
+ (dictArity dicts) rhs
- ; return (main_bind : spec_binds ++ rest) }
+ ; return (main_bind `consOL` spec_binds) }
-dsHsBind auto_scc rest (AbsBinds all_tyvars dicts exports binds)
- = do { core_prs <- ds_lhs_binds NoSccs binds
+dsHsBind auto_scc (AbsBinds { abs_tvs = all_tyvars, abs_ev_vars = dicts
+ , abs_exports = exports, abs_ev_binds = ev_binds
+ , abs_binds = binds })
+ = do { bind_prs <- ds_lhs_binds NoSccs binds
+ ; ds_ev_binds <- dsTcEvBinds ev_binds
; let env = mkABEnv exports
- ar_env = mkArityEnv binds
do_one (lcl_id,rhs) | Just (_, gbl_id, _, _prags) <- lookupVarEnv env lcl_id
= (lcl_id, addAutoScc auto_scc gbl_id rhs)
| otherwise = (lcl_id,rhs)
- -- Rec because of mixed-up dictionary bindings
- core_bind = Rec (map do_one core_prs)
+ core_bind = Rec (map do_one (fromOL bind_prs))
+ -- Monomorphic recursion possible, hence Rec
- 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 $
+ wrapDsEvBinds ds_ev_binds $
+ 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
- (lookupArity ar_env 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
- ; return ((global', rhs) : spec_binds) }
+ ; (spec_binds, rules) <- dsSpecs global
+ (Let (NonRec poly_tup_id poly_tup_rhs) rhs)
+ spec_prags
+ ; let global' = addIdSpecialisations global rules
+ ; return ((global', rhs) `consOL` spec_binds) }
where
mk_ty_arg all_tyvar
| all_tyvar `elem` tyvars = mkTyVarTy 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) :
- (concat export_binds_s ++ rest)) }
+ ; return ((poly_tup_id, poly_tup_rhs) `consOL`
+ concatOL export_binds_s) }
+
+--------------------------------------
+data DsEvBind
+ = LetEvBind -- Dictionary or coercion
+ CoreBind -- recursive or non-recursive
+
+ | CaseEvBind -- Coercion binding by superclass selection
+ -- Desugars to case d of d { K _ g _ _ _ -> ... }
+ DictId -- b The dictionary
+ AltCon -- K Its constructor
+ [CoreBndr] -- _ g _ _ _ The binders in the alternative
+wrapDsEvBinds :: [DsEvBind] -> CoreExpr -> CoreExpr
+wrapDsEvBinds ds_ev_binds body = foldr wrap_one body ds_ev_binds
+ where
+ body_ty = exprType body
+ wrap_one (LetEvBind b) body = Let b body
+ wrap_one (CaseEvBind x k xs) body = Case (Var x) x body_ty [(k,xs,body)]
+
+dsTcEvBinds :: TcEvBinds -> DsM [DsEvBind]
+dsTcEvBinds (TcEvBinds {}) = panic "dsEvBinds" -- Zonker has got rid of this
+dsTcEvBinds (EvBinds bs) = dsEvBinds bs
+
+dsEvBinds :: Bag EvBind -> DsM [DsEvBind]
+dsEvBinds bs = return (map dsEvGroup sccs)
+ where
+ sccs :: [SCC EvBind]
+ sccs = stronglyConnCompFromEdgedVertices edges
+
+ edges :: [(EvBind, EvVar, [EvVar])]
+ edges = foldrBag ((:) . mk_node) [] bs
+
+ mk_node :: EvBind -> (EvBind, EvVar, [EvVar])
+ mk_node b@(EvBind var term) = (b, var, free_vars_of term)
+
+ free_vars_of :: EvTerm -> [EvVar]
+ free_vars_of (EvId v) = [v]
+ free_vars_of (EvCast v co) = v : varSetElems (tyVarsOfType co)
+ free_vars_of (EvCoercion co) = varSetElems (tyVarsOfType co)
+ free_vars_of (EvDFunApp _ _ vs) = vs
+ free_vars_of (EvSuperClass d _) = [d]
+
+dsEvGroup :: SCC EvBind -> DsEvBind
+dsEvGroup (AcyclicSCC (EvBind co_var (EvSuperClass dict n)))
+ | isCoVar co_var -- An equality superclass
+ = ASSERT( null other_data_cons )
+ CaseEvBind dict (DataAlt data_con) bndrs
+ where
+ (cls, tys) = getClassPredTys (evVarPred dict)
+ (data_con:other_data_cons) = tyConDataCons (classTyCon cls)
+ (ex_tvs, theta, rho) = tcSplitSigmaTy (applyTys (dataConRepType data_con) tys)
+ (arg_tys, _) = splitFunTys rho
+ bndrs = ex_tvs ++ map mk_wild_pred (theta `zip` [0..])
+ ++ map mkWildValBinder arg_tys
+ mk_wild_pred (p, i) | i==n = ASSERT( p `tcEqPred` (coVarPred co_var))
+ co_var
+ | otherwise = mkWildEvBinder p
+
+dsEvGroup (AcyclicSCC (EvBind v r))
+ = LetEvBind (NonRec v (dsEvTerm r))
+
+dsEvGroup (CyclicSCC bs)
+ = LetEvBind (Rec (map ds_pair bs))
+ where
+ ds_pair (EvBind v r) = (v, dsEvTerm r)
+
+dsEvTerm :: EvTerm -> CoreExpr
+dsEvTerm (EvId v) = Var v
+dsEvTerm (EvCast v co) = Cast (Var v) co
+dsEvTerm (EvDFunApp df tys vars) = Var df `mkTyApps` tys `mkVarApps` vars
+dsEvTerm (EvCoercion co) = Type co
+dsEvTerm (EvSuperClass d n)
+ = ASSERT( isClassPred (classSCTheta cls !! n) )
+ -- We can only select *dictionary* superclasses
+ -- in terms. Equality superclasses are dealt with
+ -- in dsEvGroup, where they can generate a case expression
+ Var sc_sel_id `mkTyApps` tys `App` Var d
+ where
+ sc_sel_id = classSCSelId cls n -- Zero-indexed
+ (cls, tys) = getClassPredTys (evVarPred d)
+
------------------------
-makeCorePair :: Id-> Arity -> CoreExpr -> (Id, CoreExpr)
-makeCorePair gbl_id arity rhs
- = (addInline gbl_id arity rhs, rhs)
+makeCorePair :: Id -> Bool -> Arity -> CoreExpr -> (Id, CoreExpr)
+makeCorePair gbl_id is_default_method dict_arity rhs
+ | is_default_method -- Default methods are *always* inlined
+ = (gbl_id `setIdUnfolding` mkCompulsoryUnfolding rhs, rhs)
+
+ | not (isInlinePragma inline_prag)
+ = (gbl_id, rhs)
+
+ | Just arity <- inlinePragmaSat inline_prag
+ -- Add an Unfolding for an INLINE (but not for NOINLINE)
+ -- And eta-expand the RHS; see Note [Eta-expanding INLINE things]
+ , let real_arity = dict_arity + arity
+ -- NB: The arity in the InlineRule takes account of the dictionaries
+ = (gbl_id `setIdUnfolding` mkInlineRule rhs (Just real_arity),
+ etaExpand real_arity rhs)
+
+ | otherwise
+ = (gbl_id `setIdUnfolding` mkInlineRule rhs Nothing, rhs)
+ where
+ inline_prag = idInlinePragma gbl_id
+
+dictArity :: [Var] -> Arity
+-- Don't count coercion variables in arity
+dictArity dicts = count isId dicts
+
------------------------
-type AbsBindEnv = VarEnv ([TyVar], Id, Id, [LSpecPrag])
+type AbsBindEnv = VarEnv ([TyVar], Id, Id, TcSpecPrags)
-- Maps the "lcl_id" for an AbsBind to
-- its "gbl_id" and associated pragmas, if any
-mkABEnv :: [([TyVar], Id, Id, [LSpecPrag])] -> AbsBindEnv
+mkABEnv :: [([TyVar], Id, Id, TcSpecPrags)] -> AbsBindEnv
-- Takes the exports of a AbsBinds, and returns a mapping
-- lcl_id -> (tyvars, gbl_id, lcl_id, prags)
mkABEnv exports = mkVarEnv [ (lcl_id, export) | export@(_, _, lcl_id, _) <- exports]
+\end{code}
-mkArityEnv :: LHsBinds Id -> IdEnv Arity
- -- Maps a local to the arity of its definition
-mkArityEnv binds = foldrBag (plusVarEnv . lhsBindArity) emptyVarEnv binds
+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
-lhsBindArity :: LHsBind Id -> IdEnv Arity
-lhsBindArity (L _ (FunBind { fun_id = id, fun_matches = ms }))
- = unitVarEnv (unLoc id) (matchGroupArity ms)
-lhsBindArity (L _ (AbsBinds { abs_exports = exports
- , abs_dicts = dicts
- , abs_binds = binds }))
- = mkVarEnv [ (gbl, lookupArity ar_env lcl + n_val_dicts)
- | (_, gbl, lcl, _) <- exports]
- where -- See Note [Nested arities]
- ar_env = mkArityEnv binds
- n_val_dicts = dictArity dicts
+ AbsBinds [a,b] [ ([a,b], fg, fl, _),
+ ([b], gg, gl, _) ]
+ { fl = e1
+ gl = e2
+ h = e3 }
-lhsBindArity _ = emptyVarEnv -- PatBind/VarBind
+and desugar it to
-dictArity :: [Var] -> Arity
--- Don't count coercion variables in arity
-dictArity dicts = count isId dicts
+ fg = /\ab. let B in e1
+ gg = /\b. let a = () in let B in S(e2)
+ h = /\ab. let B in e3
-lookupArity :: IdEnv Arity -> Id -> Arity
-lookupArity ar_env id = lookupVarEnv ar_env id `orElse` 0
+where B is the *non-recursive* binding
+ fl = fg a b
+ gl = gg b
+ h = h a b -- See (b); note shadowing!
-addInline :: Id -> Arity -> CoreExpr -> Id
-addInline id arity rhs
- | isInlinePragma (idInlinePragma id)
- -- Add an Unfolding for an INLINE (but not for NOINLINE)
- = id `setIdUnfolding` mkInlineRule InlSat rhs arity
- | otherwise
- = id
-\end{code}
+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.
-Nested arities
-~~~~~~~~~~~~~~
+
+Note [Eta-expanding INLINE things]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Consider
+ foo :: Eq a => a -> a
+ {-# INLINE foo #-}
+ foo x = ...
+
+If (foo d) ever gets floated out as a common sub-expression (which can
+happen as a result of method sharing), there's a danger that we never
+get to do the inlining, which is a Terribly Bad thing given that the
+user said "inline"!
+
+To avoid this we pre-emptively eta-expand the definition, so that foo
+has the arity with which it is declared in the source code. In this
+example it has arity 2 (one for the Eq and one for x). Doing this
+should mean that (foo d) is a PAP and we don't share it.
+
+Note [Nested arities]
+~~~~~~~~~~~~~~~~~~~~~
For reasons that are not entirely clear, method bindings come out looking like
this:
It might be better to have just one level of AbsBinds, but that requires more
thought!
+Note [Implementing SPECIALISE pragmas]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+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
+
+ AbsBinds [ab] [d1,d2] [([ab], f, f_mono, prags)] binds
+
+ SpecPrag (wrap_fn :: forall a b. (Eq a, Ix b) => XXX
+ -> 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) => 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.
+
+From these we generate:
+
+ 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 <poly_rhs>
+
+Note that
+
+ * The LHS of the rule may mention dictionary *expressions* (eg
+ $dfIxPair dp dq), and that is essential because the dp, dq are
+ needed on the RHS.
+
+ * 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 -> Arity -- Global, local, arity of local
- -> CoreBind -> [LSpecPrag]
- -> DsM ( [(Id,CoreExpr)] -- Binding for specialised Ids
+dsSpecs :: Id -- The polymorphic Id
+ -> CoreExpr -- Its rhs
+ -> TcSpecPrags
+ -> DsM ( OrdList (Id,CoreExpr) -- Binding for specialised Ids
, [CoreRule] ) -- Rules for the Global Ids
--- Example:
--- f :: (Eq a, Ix b) => a -> b -> b
--- {-# SPECIALISE f :: Ix b => Int -> b -> b #-}
---
--- AbsBinds [ab] [d1,d2] [([ab], f, f_mono, prags)] binds
---
--- SpecPrag (/\b.\(d:Ix b). f Int b dInt d)
--- (forall b. Ix b => Int -> b -> b)
---
--- Rule: forall b,(d:Ix b). f Int b dInt d = f_spec b d
---
--- Spec bind: f_spec = Let f = /\ab \(d1:Eq a)(d2:Ix b). let binds in f_mono
--- /\b.\(d:Ix b). in f Int b dInt d
--- The idea is that f occurs just once, so it'll be
--- inlined and specialised
---
--- Given SpecPrag (/\as.\ds. f es) t, we have
--- the defn f_spec as ds = let-nonrec f = /\fas\fds. let f_mono = <f-rhs> in f_mono
--- in f es
--- and the RULE forall as, ds. f es = f_spec as ds
---
--- It is *possible* that 'es' does not mention all of the dictionaries 'ds'
--- (a bit silly, because then the
-
-dsSpecs all_tvs dicts tvs poly_id mono_id inl_arity mono_bind prags
- = do { pairs <- mapMaybeM spec_one prags
- ; let (spec_binds_s, rules) = unzip pairs
- ; return (concat spec_binds_s, rules) }
+-- See Note [Implementing SPECIALISE pragmas]
+dsSpecs poly_id poly_rhs prags
+ = case prags of
+ IsDefaultMethod -> return (nilOL, [])
+ SpecPrags sps -> do { pairs <- mapMaybeM spec_one sps
+ ; let (spec_binds_s, rules) = unzip pairs
+ ; return (concatOL spec_binds_s, rules) }
where
- spec_one :: LSpecPrag -> DsM (Maybe ([(Id,CoreExpr)], CoreRule))
+ spec_one :: Located TcSpecPrag -> DsM (Maybe (OrdList (Id,CoreExpr), CoreRule))
spec_one (L loc (SpecPrag spec_co spec_inl))
= putSrcSpanDs loc $
do { let poly_name = idName poly_id
; spec_name <- newLocalName poly_name
- ; wrap_fn <- dsCoercion spec_co
- ; let ds_spec_expr = wrap_fn (Var poly_id)
- ; case decomposeRuleLhs ds_spec_expr of {
+ ; wrap_fn <- dsHsWrapper spec_co
+ ; let (bndrs, ds_lhs) = collectBinders (wrap_fn (Var poly_id))
+ spec_ty = mkPiTypes bndrs (exprType ds_lhs)
+ ; case decomposeRuleLhs ds_lhs of {
Nothing -> do { warnDs (decomp_msg spec_co)
; return Nothing } ;
- Just (bndrs, _fn, args) ->
+ Just (_fn, args) ->
-- Check for dead binders: Note [Unused spec binders]
- case filter isDeadBinder bndrs of {
- bs | not (null bs) -> do { warnDs (dead_msg bs); return Nothing }
- | otherwise -> do
+ let arg_fvs = exprsFreeVars args
+ bad_bndrs = filterOut (`elemVarSet` arg_fvs) bndrs
+ in if not (null bad_bndrs)
+ then do { warnDs (dead_msg bad_bndrs); return Nothing }
+ else do
- { (spec_unf, unf_pairs) <- specUnfolding wrap_fn (idUnfolding poly_id)
+ { (spec_unf, unf_pairs) <- specUnfolding wrap_fn spec_ty (realIdUnfolding poly_id)
- ; let f_body = fix_up (Let mono_bind (Var mono_id))
- spec_ty = exprType ds_spec_expr
- spec_id = mkLocalId spec_name spec_ty
+ ; let spec_id = mkLocalId spec_name spec_ty
`setInlinePragma` inl_prag
`setIdUnfolding` spec_unf
inl_prag | isDefaultInlinePragma spec_inl = idInlinePragma poly_id
-- Get the INLINE pragma from SPECIALISE declaration, or,
-- failing that, from the original Id
- spec_id_arity = inl_arity + count isDictId bndrs
-
- extra_dict_bndrs = [ localiseId d -- See Note [Constant rule dicts]
- | d <- varSetElems (exprFreeVars ds_spec_expr)
- , isDictId d]
- -- Note [Const rule dicts]
+ extra_dict_bndrs = [ mkLocalId (localiseName (idName d)) (idType d)
+ -- See Note [Constant rule dicts]
+ | d <- varSetElems (arg_fvs `delVarSetList` bndrs)
+ , isDictId d]
rule = mkLocalRule (mkFastString ("SPEC " ++ showSDoc (ppr poly_name)))
AlwaysActive poly_name
(extra_dict_bndrs ++ bndrs) args
(mkVarApps (Var spec_id) bndrs)
- spec_rhs = wrap_fn (mkLams (tvs ++ dicts) f_body)
- spec_pair = makeCorePair spec_id spec_id_arity spec_rhs
-
- ; return (Just (spec_pair : unf_pairs, rule))
- } } } }
+ spec_rhs = wrap_fn poly_rhs
+ spec_pair = makeCorePair spec_id False (dictArity bndrs) spec_rhs
- -- 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
+ ; return (Just (spec_pair `consOL` unf_pairs, rule))
+ } } }
dead_msg bs = vcat [ sep [ptext (sLit "Useless constraint") <> plural bs
<+> ptext (sLit "in specialied type:"),
2 (pprHsWrapper (ppr poly_id) spec_co)
-specUnfolding :: (CoreExpr -> CoreExpr) -> Unfolding -> DsM (Unfolding, [(Id,CoreExpr)])
-specUnfolding wrap_fn (DFunUnfolding con ops)
+specUnfolding :: (CoreExpr -> CoreExpr) -> Type
+ -> Unfolding -> DsM (Unfolding, OrdList (Id,CoreExpr))
+specUnfolding wrap_fn spec_ty (DFunUnfolding _ _ ops)
= do { let spec_rhss = map wrap_fn ops
; spec_ids <- mapM (mkSysLocalM (fsLit "spec") . exprType) spec_rhss
- ; return (DFunUnfolding con (map Var spec_ids), spec_ids `zip` spec_rhss) }
-specUnfolding _ _
- = return (noUnfolding, [])
+ ; return (mkDFunUnfolding spec_ty (map Var spec_ids), toOL (spec_ids `zip` spec_rhss)) }
+specUnfolding _ _ _
+ = return (noUnfolding, nilOL)
+{-
mkArbitraryTypeEnv :: [TyVar] -> [([TyVar], a, b, c)] -> TyVarEnv Type
-- If any of the tyvars is missing from any of the lists in
-- the second arg, return a binding in the result
, not (tv `elemVarEnv` env)]
extend env tv = extendVarEnv env tv (dsMkArbitraryType tv)
+-}
dsMkArbitraryType :: TcTyVar -> Type
dsMkArbitraryType tv = anyTypeOfKind (tyVarKind tv)
but it seems better to reject the program because it's almost certainly
a mistake. That's what the isDeadBinder call detects.
-Note [Const rule dicts]
+Note [Constant rule dicts]
~~~~~~~~~~~~~~~~~~~~~~~
When the LHS of a specialisation rule, (/\as\ds. f es) has a free dict,
which is presumably in scope at the function definition site, we can quantify
But be careful! That dInt might be GHC.Base.$fOrdInt, which is an External
Name, and you can't bind them in a lambda or forall without getting things
-confused. Hence the use of 'localiseId' to make it Internal.
-
+confused. Likewise it might have an InlineRule or something, which would be
+utterly bogus. So we really make a fresh Id, with the same unique and type
+as the old one, but with an Internal name and no IdInfo.
%************************************************************************
%* *
%************************************************************************
\begin{code}
-decomposeRuleLhs :: CoreExpr -> Maybe ([Var], Id, [CoreExpr])
+decomposeRuleLhs :: CoreExpr -> Maybe (Id, [CoreExpr])
-- Take apart the LHS of a RULE. It's suuposed to look like
-- /\a. f a Int dOrdInt
-- or /\a.\d:Ord a. let { dl::Ord [a] = dOrdList a d } in f [a] dl
-- That is, the RULE binders are lambda-bound
-- Returns Nothing if the LHS isn't of the expected shape
decomposeRuleLhs lhs
- = case collectArgs body of
- (Var fn, args) -> Just (bndrs, fn, args)
+ = -- Note [Simplifying the left-hand side of a RULE]
+ case collectArgs (simpleOptExpr lhs) of
+ (Var fn, args) -> Just (fn, args)
(Case scrut bndr ty [(DEFAULT, _, body)], args)
| isDeadBinder bndr -- Note [Matching seqId]
- -> Just (bndrs, seqId, args' ++ args)
+ -> Just (seqId, args' ++ args)
where
args' = [Type (idType bndr), Type ty, scrut, body]
_other -> Nothing -- Unexpected shape
- where
- (bndrs, body) = collectBinders (simpleOptExpr lhs)
- -- simpleOptExpr occurrence-analyses and simplifies the lhs
- -- and thereby
- -- (a) identifies unused binders: Note [Unused spec binders]
- -- (b) sorts dict bindings into NonRecs
- -- so they can be inlined by 'decomp'
- -- (c) substitute trivial lets so that they don't get in the way
- -- Note that we substitute the function too; we might
- -- have this as a LHS: let f71 = M.f Int in f71
- -- NB: tcSimplifyRuleLhs is very careful not to generate complicated
- -- dictionary expressions that we might have to match
\end{code}
+Note [Simplifying the left-hand side of a RULE]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+simpleOptExpr occurrence-analyses and simplifies the lhs
+and thereby
+(a) sorts dict bindings into NonRecs and inlines them
+(b) substitute trivial lets so that they don't get in the way
+ Note that we substitute the function too; we might
+ have this as a LHS: let f71 = M.f Int in f71
+(c) does eta reduction
+
+For (c) consider the fold/build rule, which without simplification
+looked like:
+ fold k z (build (/\a. g a)) ==> ...
+This doesn't match unless you do eta reduction on the build argument.
+Similarly for a LHS like
+ augment g (build h)
+we do not want to get
+ augment (\a. g a) (build h)
+otherwise we don't match when given an argument like
+ augment (\a. h a a) (build h)
+
+NB: tcSimplifyRuleLhs is very careful not to generate complicated
+ dictionary expressions that we might have to match
+
+
Note [Matching seqId]
~~~~~~~~~~~~~~~~~~~
The desugarer turns (seq e r) into (case e of _ -> r), via a special-case hack
data AutoScc = NoSccs
| AddSccs Module (Id -> Bool)
-- The (Id->Bool) says which Ids to add SCCs to
+-- But we never add a SCC to function marked INLINE
addAutoScc :: AutoScc
-> Id -- Binder
addAutoScc NoSccs _ rhs
= rhs
+addAutoScc _ id rhs | isInlinePragma (idInlinePragma id)
+ = rhs
addAutoScc (AddSccs mod add_scc) id rhs
| add_scc id = mkSCC (mkAutoCC id mod NotCafCC) rhs
| otherwise = rhs
\begin{code}
-dsCoercion :: HsWrapper -> DsM (CoreExpr -> CoreExpr)
-dsCoercion WpHole = return (\e -> e)
-dsCoercion (WpCompose c1 c2) = do { k1 <- dsCoercion c1
- ; k2 <- dsCoercion c2
- ; return (k1 . k2) }
-dsCoercion (WpCast co) = return (\e -> Cast e co)
-dsCoercion (WpLam id) = return (\e -> Lam id e)
-dsCoercion (WpTyLam tv) = return (\e -> Lam tv e)
-dsCoercion (WpApp v) | isTyVar v -- Probably a coercion var
- = return (\e -> App e (Type (mkTyVarTy v)))
- | otherwise
- = return (\e -> App e (Var v))
-dsCoercion (WpTyApp ty) = return (\e -> App e (Type ty))
-dsCoercion (WpLet bs) = do { prs <- dsLHsBinds bs
- ; return (\e -> Let (Rec prs) e) }
+dsHsWrapper :: HsWrapper -> DsM (CoreExpr -> CoreExpr)
+dsHsWrapper WpHole = return (\e -> e)
+dsHsWrapper (WpTyApp ty) = return (\e -> App e (Type ty))
+dsHsWrapper (WpLet ev_binds) = do { ds_ev_binds <- dsTcEvBinds ev_binds
+ ; return (wrapDsEvBinds ds_ev_binds) }
+dsHsWrapper (WpCompose c1 c2) = do { k1 <- dsHsWrapper c1
+ ; k2 <- dsHsWrapper c2
+ ; return (k1 . k2) }
+dsHsWrapper (WpCast co) = return (\e -> Cast e co)
+dsHsWrapper (WpEvLam ev) = return (\e -> Lam ev e)
+dsHsWrapper (WpTyLam tv) = return (\e -> Lam tv e)
+dsHsWrapper (WpEvApp evtrm) = return (\e -> App e (dsEvTerm evtrm))
\end{code}
projects / ghc-hetmet.git / blobdiff