#include "HsVersions.h"
-import {-# SOURCE #-} DsExpr( dsLExpr, dsExpr )
+import {-# SOURCE #-} DsExpr( dsLExpr )
import {-# SOURCE #-} Match( matchWrapper )
import DsMonad
import DsGRHSs
import DsUtils
-import OccurAnal
import HsSyn -- lots of things
import CoreSyn -- lots of things
+import CoreSubst
import MkCore
import CoreUtils
+import CoreArity ( etaExpand )
+import CoreUnfold
import CoreFVs
-import TcHsSyn ( mkArbitraryType ) -- Mis-placed?
import TcType
+import TysPrim ( anyTypeOfKind )
import CostCentre
import Module
import Id
-import Var ( Var, TyVar )
+import Name ( localiseName )
+import MkId ( seqId )
+import Var ( Var, TyVar, tyVarKind )
+import IdInfo ( vanillaIdInfo )
import VarSet
import Rules
import VarEnv
-import Type
import Outputable
import SrcLoc
import Maybes
import BasicTypes hiding ( TopLevel )
import FastString
import StaticFlags ( opt_DsMultiTyVar )
-import Util ( mapSnd, mapAndUnzip, lengthExceeds )
+import Util ( count, lengthExceeds )
+import MonadUtils
import Control.Monad
-import Data.List
\end{code}
%************************************************************************
------------------------
ds_lhs_binds :: AutoScc -> LHsBinds Id -> DsM [(Id,CoreExpr)]
+
-- scc annotation policy (see below)
ds_lhs_binds auto_scc binds = foldM (dsLHsBind auto_scc) [] (bagToList binds)
-> HsBind Id
-> DsM [(Id,CoreExpr)] -- Result
-dsHsBind _ rest (VarBind var expr) = do
- core_expr <- dsLExpr expr
-
- -- Dictionary bindings are always VarMonoBinds, so
- -- we only need do this here
- core_expr' <- addDictScc var core_expr
- return ((var, core_expr') : rest)
-
-dsHsBind _ rest (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
- rhs <- dsCoercion co_fn (return (mkLams args body'))
- return ((fun,rhs) : rest)
-
-dsHsBind _ rest (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 _ rest (VarBind { var_id = var, var_rhs = expr, var_inline = inline_regardless })
+ = do { core_expr <- dsLExpr expr
+
+ -- Dictionary bindings are always VarBinds,
+ -- so we only need do this here
+ ; core_expr' <- addDictScc var core_expr
+ ; let var' | inline_regardless = var `setIdUnfolding` mkCompulsoryUnfolding core_expr'
+ | otherwise = var
+
+ ; return ((var', core_expr') : rest) }
+
+dsHsBind _ rest
+ (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) }
+
+dsHsBind _ rest
+ (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) }
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, _, prags) <- lookupVarEnv env lcl_id
- = addInlinePrags prags gbl_id $
- addAutoScc auto_scc gbl_id rhs
- | otherwise = (lcl_id, rhs)
+ do_one (lcl_id, rhs)
+ | Just (_, gbl_id, _, spec_prags) <- lookupVarEnv env lcl_id
+ = 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 = 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
-- see if it has any impact; it is on by default
= -- Note [Abstracting over tyvars only]
do { core_prs <- ds_lhs_binds NoSccs binds
- ; arby_env <- mkArbitraryTypeEnv tyvars exports
- ; let (lg_binds, core_prs') = mapAndUnzip do_one core_prs
+ ; let arby_env = mkArbitraryTypeEnv tyvars exports
bndrs = mkVarSet (map fst core_prs)
add_lets | core_prs `lengthExceeds` 10 = add_some
- | otherwise = mkLets lg_binds
- add_some rhs = mkLets [ NonRec b r | NonRec b r <- lg_binds
- , b `elemVarSet` fvs] rhs
+ | otherwise = mkLets
+ add_some lg_binds rhs = mkLets [ NonRec b r | NonRec b r <- lg_binds
+ , b `elemVarSet` fvs] rhs
where
fvs = exprSomeFreeVars (`elemVarSet` bndrs) rhs
env = mkABEnv exports
-
- do_one (lcl_id, rhs)
- | Just (id_tvs, gbl_id, _, prags) <- lookupVarEnv env lcl_id
- = (NonRec lcl_id (mkTyApps (Var gbl_id) (mkTyVarTys id_tvs)),
- addInlinePrags prags gbl_id $
- 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 rhs)
+ mk_lg_bind lcl_id gbl_id tyvars
+ = NonRec (setIdInfo lcl_id vanillaIdInfo)
+ -- Nuke the IdInfo so that no old unfoldings
+ -- confuse use (it might mention something not
+ -- even in scope at the new site
+ (mkTyApps (Var gbl_id) (mkTyVarTys tyvars))
+
+ do_one lg_binds (lcl_id, rhs)
+ | Just (id_tvs, gbl_id, _, spec_prags) <- lookupVarEnv env lcl_id
+ = 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
- = (NonRec lcl_id (mkTyApps (Var non_exp_gbl_id) (mkTyVarTys tyvars)),
- (non_exp_gbl_id, mkLams tyvars (add_lets rhs)))
- where
- non_exp_gbl_id = setIdType lcl_id (mkForAllTys tyvars (idType lcl_id))
+ = 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))]) }
- ; return (core_prs' ++ rest) }
+ ; (_, core_prs') <- fixDs (\ ~(lg_binds, _) -> mapAndUnzipM (do_one lg_binds) core_prs)
+ ; return (concat core_prs' ++ rest) }
-- Another 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)
- = ASSERT( all (`elem` tyvars) all_tyvars ) do
- core_prs <- ds_lhs_binds NoSccs binds
- let
- -- Always treat the binds as recursive, because the typechecker
- -- makes rather mixed-up dictionary bindings
- core_bind = Rec core_prs
+ = ASSERT( all (`elem` tyvars) all_tyvars )
+ do { core_prs <- ds_lhs_binds NoSccs binds
+
+ ; 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)
- mb_specs <- mapM (dsSpec all_tyvars dicts tyvars global local core_bind) prags
- let
- (spec_binds, rules) = unzip (catMaybes mb_specs)
- global' = addIdSpecialisations global rules
- rhs' = mkLams tyvars $ mkLams dicts $ Let core_bind (Var local)
- bind = addInlinePrags prags global' $ addAutoScc auto_scc global' rhs'
+ ; (spec_binds, rules) <- dsSpecs global rhs prags
+
+ ; let global' = addIdSpecialisations global rules
+ main_bind = makeCorePair global' (isDefaultMethod prags)
+ (dictArity dicts) rhs
- return (bind : spec_binds ++ rest)
+ ; return (main_bind : spec_binds ++ rest) }
dsHsBind auto_scc rest (AbsBinds all_tyvars dicts exports binds)
= do { core_prs <- ds_lhs_binds NoSccs binds
; let env = mkABEnv exports
- do_one (lcl_id,rhs) | Just (_, gbl_id, _, prags) <- lookupVarEnv env lcl_id
- = addInlinePrags prags lcl_id $
- addAutoScc auto_scc gbl_id rhs
+ 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)
- 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 dict_args = map Var dicts
-
- mk_bind ((tyvars, global, local, 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 { ty_args <- mapM mk_ty_arg all_tyvars
- ; let substitute = substTyWith all_tyvars ty_args
+ ; 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)
- ; mb_specs <- mapM (dsSpec all_tyvars dicts tyvars global local core_bind)
- prags
- ; let (spec_binds, rules) = unzip (catMaybes mb_specs)
- global' = addIdSpecialisations global rules
- rhs = mkLams tyvars $ mkLams dicts $
+ ; let rhs = mkLams tyvars $ mkLams dicts $
mkTupleSelector locals' (locals' !! n) tup_id $
- mkApps (mkTyApps (Var poly_tup_id) ty_args) dict_args
+ 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
- | all_tyvar `elem` tyvars = return (mkTyVarTy all_tyvar)
+ | all_tyvar `elem` tyvars = mkTyVarTy all_tyvar
| otherwise = dsMkArbitraryType all_tyvar
; export_binds_s <- mapM mk_bind (exports `zip` [0..])
- -- don't scc (auto-)annotate the tuple itself.
+ -- 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 :: [([TyVar], Id, Id, [LPrag])] -> VarEnv ([TyVar], Id, Id, [LPrag])
+------------------------
+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, TcSpecPrags)
+ -- Maps the "lcl_id" for an AbsBind to
+ -- its "gbl_id" and associated pragmas, if any
+
+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}
+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
-dsSpec :: [TyVar] -> [DictId] -> [TyVar]
- -> Id -> Id -- Global, local
- -> CoreBind -> LPrag
- -> DsM (Maybe ((Id,CoreExpr), -- Binding for specialised Id
- CoreRule)) -- Rule for the Global Id
-
--- 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
-dsSpec _ _ _ _ _ _ (L _ (InlinePrag {}))
- = return Nothing
-
-dsSpec all_tvs dicts tvs poly_id mono_id mono_bind
- (L loc (SpecPrag spec_expr spec_ty inl))
- = putSrcSpanDs loc $
- do { let poly_name = idName poly_id
- ; spec_name <- newLocalName poly_name
- ; ds_spec_expr <- dsExpr spec_expr
- ; case (decomposeRuleLhs ds_spec_expr) of {
- Nothing -> do { warnDs decomp_msg; return Nothing } ;
-
- Just (bndrs, _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
-
- { f_body <- fix_up (Let mono_bind (Var mono_id))
-
- ; let local_poly = setIdNotExported poly_id
- -- Very important to make the 'f' non-exported,
- -- else it won't be inlined!
- spec_id = mkLocalId spec_name spec_ty
- spec_rhs = Let (NonRec local_poly poly_f_body) ds_spec_expr
- poly_f_body = mkLams (tvs ++ dicts) f_body
-
- extra_dict_bndrs = [localiseId d -- See Note [Constant rule dicts]
- | d <- varSetElems (exprFreeVars ds_spec_expr)
- , isDictId d]
- -- Note [Const rule dicts]
-
- rule = mkLocalRule (mkFastString ("SPEC " ++ showSDoc (ppr poly_name)))
- AlwaysActive poly_name
- (extra_dict_bndrs ++ bndrs) args
- (mkVarApps (Var spec_id) bndrs)
- ; return (Just (addInlineInfo inl spec_id spec_rhs, rule))
- } } } }
- where
- -- Bind to Any any of all_ptvs that aren't
- -- relevant for this particular function
- fix_up body | null void_tvs = return body
- | otherwise = do { void_tys <- mapM dsMkArbitraryType void_tvs
- ; return (mkTyApps (mkLams void_tvs body) void_tys) }
+ 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
+ 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"!
- void_tvs = all_tvs \\ tvs
+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:
+
+ AbsBinds [] [] [$cfromT <= [] fromT]
+ $cfromT [InlPrag=INLINE] :: T Bool -> Bool
+ { AbsBinds [] [] [fromT <= [] fromT_1]
+ fromT :: T Bool -> Bool
+ { fromT_1 ((TBool b)) = not b } } }
+
+Note the nested AbsBind. The arity for the InlineRule on $cfromT should be
+gotten from the binding for fromT_1.
+
+It might be better to have just one level of AbsBinds, but that requires more
+thought!
+
+Note [Implementing SPECIALISE pragmas]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Example:
+ f :: (Eq a, Ix b) => a -> b -> Bool
+ {-# SPECIALISE f :: (Ix p, Ix q) => Int -> (p,q) -> Bool #-}
+ f = <poly_rhs>
+
+From this the typechecker generates
+
+ AbsBinds [ab] [d1,d2] [([ab], f, f_mono, prags)] binds
+
+ SpecPrag (wrap_fn :: forall a b. (Eq a, Ix b) => XXX
+ -> forall p q. (Ix p, Ix q) => XXX[ Int/a, (p,q)/b ])
+
+Note that wrap_fn can transform *any* function with the right type prefix
+ forall ab. (Eq a, Ix b) => XXX
+regardless of XXX. It's sort of polymorphic in XXX. This is
+useful: we use the same wrapper to transform each of the class ops, as
+well as the dict.
+
+From these we generate:
+
+ Rule: forall p, q, (dp:Ix p), (dq:Ix q).
+ f Int (p,q) dInt ($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 :: 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 poly_id poly_rhs prags
+ = case prags of
+ IsDefaultMethod -> return ([], [])
+ SpecPrags sps -> do { pairs <- mapMaybeM spec_one sps
+ ; let (spec_binds_s, rules) = unzip pairs
+ ; return (concat spec_binds_s, rules) }
+ where
+ spec_one :: Located TcSpecPrag -> DsM (Maybe ([(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)
+ spec_ty = exprType ds_spec_expr
+ ; case decomposeRuleLhs ds_spec_expr of {
+ Nothing -> do { warnDs (decomp_msg spec_co)
+ ; return Nothing } ;
+
+ Just (bndrs, _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
+
+ { (spec_unf, unf_pairs) <- specUnfolding wrap_fn spec_ty (realIdUnfolding poly_id)
+
+ ; let spec_id = mkLocalId spec_name spec_ty
+ `setInlinePragma` inl_prag
+ `setIdUnfolding` spec_unf
+ inl_prag | isDefaultInlinePragma spec_inl = idInlinePragma poly_id
+ | otherwise = spec_inl
+ -- Get the INLINE pragma from SPECIALISE declaration, or,
+ -- failing that, from the original Id
+
+ extra_dict_bndrs = [ mkLocalId (localiseName (idName d)) (idType d)
+ -- See Note [Constant rule dicts]
+ | d <- varSetElems (exprFreeVars ds_spec_expr)
+ , 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 poly_rhs
+ spec_pair = makeCorePair spec_id False (dictArity bndrs) spec_rhs
+
+ ; return (Just (spec_pair : unf_pairs, rule))
+ } } } }
dead_msg bs = vcat [ sep [ptext (sLit "Useless constraint") <> plural bs
<+> ptext (sLit "in specialied type:"),
, ptext (sLit "SPECIALISE pragma ignored")]
get_pred b = ASSERT( isId b ) expectJust "dsSpec" (tcSplitPredTy_maybe (idType b))
- decomp_msg = hang (ptext (sLit "Specialisation too complicated to desugar; ignored"))
- 2 (ppr spec_expr)
+ decomp_msg spec_co
+ = hang (ptext (sLit "Specialisation too complicated to desugar; ignored"))
+ 2 (pprHsWrapper (ppr poly_id) spec_co)
-mkArbitraryTypeEnv :: [TyVar] -> [([TyVar], a, b, c)] -> DsM (TyVarEnv Type)
+specUnfolding :: (CoreExpr -> CoreExpr) -> Type
+ -> Unfolding -> DsM (Unfolding, [(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 (mkDFunUnfolding spec_ty (map Var spec_ids), spec_ids `zip` spec_rhss) }
+specUnfolding _ _ _
+ = return (noUnfolding, [])
+
+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
mkArbitraryTypeEnv tyvars exports
= go emptyVarEnv exports
where
- go env [] = return env
+ go env [] = env
go env ((ltvs, _, _, _) : exports)
- = do { env' <- foldlM extend env [tv | tv <- tyvars
- , not (tv `elem` ltvs)
- , not (tv `elemVarEnv` env)]
- ; go env' exports }
+ = go env' exports
+ where
+ env' = foldl extend env [tv | tv <- tyvars
+ , not (tv `elem` ltvs)
+ , not (tv `elemVarEnv` env)]
- extend env tv = do { ty <- dsMkArbitraryType tv
- ; return (extendVarEnv env tv ty) }
+ extend env tv = extendVarEnv env tv (dsMkArbitraryType tv)
-
-dsMkArbitraryType :: TcTyVar -> DsM Type
-dsMkArbitraryType tv = mkArbitraryType warn tv
- where
- warn span msg = putSrcSpanDs span (warnDs msg)
+dsMkArbitraryType :: TcTyVar -> Type
+dsMkArbitraryType tv = anyTypeOfKind (tyVarKind tv)
\end{code}
Note [Unused spec binders]
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
{-# SPECIALISE f :: Int -> Int #-}
Then we get the SpecPrag
- SpecPrag (f Int dInt) Int
+ SpecPrag (f Int dInt)
And from that we want the rule
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.
%************************************************************************
%* *
-- That is, the RULE binders are lambda-bound
-- Returns Nothing if the LHS isn't of the expected shape
decomposeRuleLhs lhs
- = case (decomp emptyVarEnv body) of
- Nothing -> Nothing
- Just (fn, args) -> Just (bndrs, fn, args)
- where
- occ_lhs = occurAnalyseExpr lhs
- -- The occurrence-analysis does two things
- -- (a) identifies unused binders: Note [Unused spec binders]
- -- (b) sorts dict bindings into NonRecs
- -- so they can be inlined by 'decomp'
- (bndrs, body) = collectBinders occ_lhs
-
- -- Substitute dicts in the LHS args, so that there
- -- aren't any lets getting in the way
- -- Note that we substitute the function too; we might have this as
- -- a LHS: let f71 = M.f Int in f71
- decomp env (Let (NonRec dict rhs) body)
- = decomp (extendVarEnv env dict (simpleSubst env rhs)) body
- decomp env body
- = case collectArgs (simpleSubst env body) of
- (Var fn, args) -> Just (fn, args)
- _ -> Nothing
-
-simpleSubst :: IdEnv CoreExpr -> CoreExpr -> CoreExpr
--- Similar to CoreSubst.substExpr, except that
--- (a) Takes no account of capture; at this point there is no shadowing
--- (b) Can have a GlobalId (imported) in its domain
--- (c) Ids only; no types are substituted
--- (d) Does not insist (as does CoreSubst.lookupIdSubst) that the
--- in-scope set mentions all LocalIds mentioned in the argument of the subst
---
--- (b) and (d) are the reasons we can't use CoreSubst
---
--- (I had a note that (b) is "no longer relevant", and indeed it doesn't
--- look relevant here. Perhaps there was another caller of simpleSubst.)
-
-simpleSubst subst expr
- = go expr
- where
- go (Var v) = lookupVarEnv subst v `orElse` Var v
- go (Cast e co) = Cast (go e) co
- go (Type ty) = Type ty
- go (Lit lit) = Lit lit
- go (App fun arg) = App (go fun) (go arg)
- go (Note note e) = Note note (go e)
- go (Lam bndr body) = Lam bndr (go body)
- go (Let (NonRec bndr rhs) body) = Let (NonRec bndr (go rhs)) (go body)
- go (Let (Rec pairs) body) = Let (Rec (mapSnd go pairs)) (go body)
- go (Case scrut bndr ty alts) = Case (go scrut) bndr ty
- [(c,bs,go r) | (c,bs,r) <- alts]
-
-addInlinePrags :: [LPrag] -> Id -> CoreExpr -> (Id,CoreExpr)
-addInlinePrags prags bndr rhs
- = case [inl | L _ (InlinePrag inl) <- prags] of
- [] -> (bndr, rhs)
- (inl:_) -> addInlineInfo inl bndr rhs
-
-addInlineInfo :: InlineSpec -> Id -> CoreExpr -> (Id,CoreExpr)
-addInlineInfo (Inline prag is_inline) bndr rhs
- = (attach_pragma bndr prag, wrap_inline is_inline rhs)
- where
- attach_pragma bndr prag
- | isDefaultInlinePragma prag = bndr
- | otherwise = bndr `setInlinePragma` prag
+ = case collectArgs body of
+ (Var fn, args) -> Just (bndrs, fn, args)
- wrap_inline True body = mkInlineMe body
- wrap_inline False body = body
+ (Case scrut bndr ty [(DEFAULT, _, body)], args)
+ | isDeadBinder bndr -- Note [Matching seqId]
+ -> Just (bndrs, 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 [Matching seqId]
+~~~~~~~~~~~~~~~~~~~
+The desugarer turns (seq e r) into (case e of _ -> r), via a special-case hack
+and this code turns it back into an application of seq!
+See Note [Rules for seq] in MkId for the details.
+
%************************************************************************
%* *
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 -> DsM CoreExpr
-dsCoercion WpHole thing_inside = thing_inside
-dsCoercion (WpCompose c1 c2) thing_inside = dsCoercion c1 (dsCoercion c2 thing_inside)
-dsCoercion (WpCast co) thing_inside = do { expr <- thing_inside
- ; return (Cast expr co) }
-dsCoercion (WpLam id) thing_inside = do { expr <- thing_inside
- ; return (Lam id expr) }
-dsCoercion (WpTyLam tv) thing_inside = do { expr <- thing_inside
- ; return (Lam tv expr) }
-dsCoercion (WpApp v) thing_inside
- | isTyVar v = do { expr <- thing_inside
- {- Probably a coercion var -} ; return (App expr (Type (mkTyVarTy v))) }
- | otherwise = do { expr <- thing_inside
- {- An Id -} ; return (App expr (Var v)) }
-dsCoercion (WpTyApp ty) thing_inside = do { expr <- thing_inside
- ; return (App expr (Type ty)) }
-dsCoercion WpInline thing_inside = do { expr <- thing_inside
- ; return (mkInlineMe expr) }
-dsCoercion (WpLet bs) thing_inside = do { prs <- dsLHsBinds bs
- ; expr <- thing_inside
- ; return (Let (Rec prs) expr) }
+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) }
\end{code}
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