lower levels it is preserved with @let@/@letrec@s).
\begin{code}
-{-# OPTIONS -w #-}
--- The above warning supression flag is a temporary kludge.
--- While working on this module you are encouraged to remove it and fix
--- any warnings in the module. See
--- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
--- for details
-
module DsBinds ( dsTopLHsBinds, dsLHsBinds, decomposeRuleLhs,
dsCoercion,
AutoScc(..)
import DsMonad
import DsGRHSs
import DsUtils
+import OccurAnal
import HsSyn -- lots of things
import CoreSyn -- lots of things
+import MkCore
import CoreUtils
import CoreFVs
-import TcHsSyn ( mkArbitraryType ) -- Mis-placed?
+import TcHsSyn ( mkArbitraryType ) -- Mis-placed?
import TcType
-import OccurAnal
import CostCentre
import Module
import Id
-import Var ( TyVar )
+import MkId ( seqId )
+import Var ( Var, TyVar )
import VarSet
import Rules
import VarEnv
import Bag
import BasicTypes hiding ( TopLevel )
import FastString
-import Util ( mapSnd )
+import StaticFlags ( opt_DsMultiTyVar )
+import Util ( mapSnd, mapAndUnzip, lengthExceeds )
import Control.Monad
import Data.List
-> HsBind Id
-> DsM [(Id,CoreExpr)] -- Result
-dsHsBind auto_scc rest (VarBind var expr) = do
+dsHsBind _ rest (VarBind var expr) = do
core_expr <- dsLExpr expr
-- Dictionary bindings are always VarMonoBinds, so
core_expr' <- addDictScc var core_expr
return ((var, core_expr') : rest)
-dsHsBind auto_scc rest (FunBind { fun_id = L _ fun, fun_matches = matches,
+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 auto_scc rest (PatBind { pat_lhs = pat, pat_rhs = grhss, pat_rhs_ty = ty }) = do
+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
+{- 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, prags) <- lookupVarEnv env lcl_id
+ 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)
locals' = [(lcl_id, Var gbl_id) | (_, gbl_id, lcl_id, _) <- exports]
+ -- Note [Rules and inlining]
; return (map do_one core_prs ++ 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
+ 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
+ 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)
+ | 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))
+
+ ; return (core_prs' ++ rest) }
+
-- Another common case: one exported variable
-- Non-recursive bindings come through this way
dsHsBind auto_scc rest
- (AbsBinds all_tyvars dicts exports@[(tyvars, global, local, prags)] binds)
+ (AbsBinds all_tyvars dicts [(tyvars, global, local, prags)] binds)
= ASSERT( all (`elem` tyvars) all_tyvars ) do
core_prs <- ds_lhs_binds NoSccs binds
let
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
+ do_one (lcl_id,rhs) | Just (_, gbl_id, _, prags) <- lookupVarEnv env lcl_id
= addInlinePrags prags lcl_id $
addAutoScc auto_scc gbl_id rhs
| otherwise = (lcl_id,rhs)
; return ((poly_tup_id, poly_tup_expr) :
(concat export_binds_s ++ rest)) }
-mkABEnv :: [([TyVar], Id, Id, [LPrag])] -> VarEnv (Id, [LPrag])
+mkABEnv :: [([TyVar], Id, Id, [LPrag])] -> VarEnv ([TyVar], Id, Id, [LPrag])
-- Takes the exports of a AbsBinds, and returns a mapping
--- lcl_id -> (gbl_id, prags)
-mkABEnv exports = mkVarEnv [ (lcl_id, (gbl_id, prags))
- | (_, gbl_id, lcl_id, prags) <- exports]
+-- lcl_id -> (tyvars, gbl_id, lcl_id, prags)
+mkABEnv exports = mkVarEnv [ (lcl_id, export) | export@(_, _, lcl_id, _) <- exports]
dsSpec :: [TyVar] -> [DictId] -> [TyVar]
--
-- It is *possible* that 'es' does not mention all of the dictionaries 'ds'
-- (a bit silly, because then the
-dsSpec all_tvs dicts tvs poly_id mono_id mono_bind (L _ (InlinePrag {}))
+dsSpec _ _ _ _ _ _ (L _ (InlinePrag {}))
= return Nothing
dsSpec all_tvs dicts tvs poly_id mono_id mono_bind
do { let poly_name = idName poly_id
; spec_name <- newLocalName poly_name
; ds_spec_expr <- dsExpr spec_expr
- ; let (bndrs, body) = collectBinders (occurAnalyseExpr ds_spec_expr)
- -- 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 decomposeRuleLhs
- mb_lhs = decomposeRuleLhs body
+ ; case (decomposeRuleLhs ds_spec_expr) of {
+ Nothing -> do { warnDs decomp_msg; return Nothing } ;
- -- 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 ->
+ Just (bndrs, _fn, args) ->
- case mb_lhs of
- Nothing -> do { warnDs decomp_msg; return Nothing }
+ -- 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
- Just (var, args) -> do
-
{ f_body <- fix_up (Let mono_bind (Var mono_id))
; let local_poly = setIdNotExported poly_id
spec_rhs = Let (NonRec local_poly poly_f_body) ds_spec_expr
poly_f_body = mkLams (tvs ++ dicts) f_body
- extra_dict_bndrs = filter isDictId (varSetElems (exprFreeVars ds_spec_expr))
+ 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)))
(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
void_tvs = all_tvs \\ tvs
- dead_msg bs = vcat [ sep [ptext SLIT("Useless constraint") <> plural bs
- <+> ptext SLIT("in specialied type:"),
+ dead_msg bs = vcat [ sep [ptext (sLit "Useless constraint") <> plural bs
+ <+> ptext (sLit "in specialied type:"),
nest 2 (pprTheta (map get_pred bs))]
- , ptext SLIT("SPECIALISE pragma ignored")]
+ , 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"))
+ decomp_msg = hang (ptext (sLit "Specialisation too complicated to desugar; ignored"))
2 (ppr spec_expr)
+
+
+mkArbitraryTypeEnv :: [TyVar] -> [([TyVar], a, b, c)] -> DsM (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 ((ltvs, _, _, _) : exports)
+ = do { env' <- foldlM extend env [tv | tv <- tyvars
+ , not (tv `elem` ltvs)
+ , not (tv `elemVarEnv` env)]
+ ; go env' exports }
+
+ extend env tv = do { ty <- dsMkArbitraryType tv
+ ; return (extendVarEnv env tv ty) }
+
+dsMkArbitraryType :: TcTyVar -> DsM Type
dsMkArbitraryType tv = mkArbitraryType warn tv
where
warn span msg = putSrcSpanDs span (warnDs msg)
RULE forall dInt. f Int dInt = f_spec
f_spec = let f = <rhs> in f Int dInt
+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.
%************************************************************************
%************************************************************************
\begin{code}
-decomposeRuleLhs :: CoreExpr -> Maybe (Id, [CoreExpr])
+decomposeRuleLhs :: CoreExpr -> Maybe ([Var], 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
- = go emptyVarEnv (occurAnalyseExpr lhs) -- Occurrence analysis sorts out the dict
- -- bindings so we know if they are recursive
+ = case (decomp emptyVarEnv body) of
+ Nothing -> Nothing
+ Just (fn, args) -> Just (bndrs, fn, args)
where
- -- 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
- go env (Let (NonRec dict rhs) body)
- = go (extendVarEnv env dict (simpleSubst env rhs)) body
- go env body
- = case collectArgs (simpleSubst env body) of
- (Var fn, args) -> Just (fn, args)
- other -> Nothing
+ 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 (Case scrut bndr ty [(DEFAULT, _, body)])
+ | isDeadBinder bndr -- Note [Matching seqId]
+ = Just (seqId, [Type (idType bndr), Type ty,
+ simpleSubst env scrut, simpleSubst env 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; dictionary bindings use new names
--- (b) can have a GlobalId (imported) in its domain
+-- (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) is the reason we can't use CoreSubst... and it's no longer relevant
--- so really we should replace simpleSubst
+-- (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
(inl:_) -> addInlineInfo inl bndr rhs
addInlineInfo :: InlineSpec -> Id -> CoreExpr -> (Id,CoreExpr)
-addInlineInfo (Inline phase is_inline) bndr rhs
- = (attach_phase bndr phase, wrap_inline is_inline rhs)
+addInlineInfo (Inline prag is_inline) bndr rhs
+ = (attach_pragma bndr prag, wrap_inline is_inline rhs)
where
- attach_phase bndr phase
- | isAlwaysActive phase = bndr -- Default phase
- | otherwise = bndr `setInlinePragma` phase
+ attach_pragma bndr prag
+ | isDefaultInlinePragma prag = bndr
+ | otherwise = bndr `setInlinePragma` prag
wrap_inline True body = mkInlineMe body
wrap_inline False body = body
\end{code}
+Note [Matching seq]
+~~~~~~~~~~~~~~~~~~~
+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.
+
%************************************************************************
%* *
wrap the dict in @_scc_ DICT <dict>@:
\begin{code}
-addDictScc var rhs = return rhs
+addDictScc :: Id -> CoreExpr -> DsM CoreExpr
+addDictScc _ rhs = return rhs
{- DISABLED for now (need to somehow make up a name for the scc) -- SDM
| not ( opt_SccProfilingOn && opt_AutoSccsOnDicts)
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 (WpCo co) thing_inside = do { expr <- 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 id) thing_inside = do { expr <- thing_inside
- ; return (App expr (Var id)) }
+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
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