import CoreUtils
import TcHsSyn ( mkArbitraryType ) -- Mis-placed?
+import TcType
import OccurAnal
import CostCentre
import Module
import Id
+import Var ( TyVar )
import Rules
-import Var ( TyVar, Var )
import VarEnv
import Type
-import TysWiredIn
import Outputable
import SrcLoc
import Maybes
import FastString
import Util ( mapSnd )
-import Name
-import OccName
-import Literal
import Control.Monad
import Data.List
; returnDs ((poly_tup_id, poly_tup_expr) :
(concat export_binds_s ++ rest)) }
-mkABEnv :: [([TyVar], Id, Id, [Prag])] -> VarEnv (Id, [Prag])
+mkABEnv :: [([TyVar], Id, Id, [LPrag])] -> VarEnv (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))
dsSpec :: [TyVar] -> [DictId] -> [TyVar]
-> Id -> Id -- Global, local
- -> CoreBind -> Prag
+ -> CoreBind -> LPrag
-> DsM (Maybe ((Id,CoreExpr), -- Binding for specialised Id
CoreRule)) -- Rule for the Global Id
-- /\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
-
-dsSpec all_tvs dicts tvs poly_id mono_id mono_bind (InlinePrag {})
+--
+-- Given SpecPrag (/\as.\ds. f es) t, we have
+-- the defn f_spec as ds = f es
+-- and the RULE 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 all_tvs dicts tvs poly_id mono_id mono_bind (L _ (InlinePrag {}))
= return Nothing
dsSpec all_tvs dicts tvs poly_id mono_id mono_bind
- (SpecPrag spec_expr spec_ty const_dicts inl)
- = do { let poly_name = idName poly_id
+ (L loc (SpecPrag spec_expr spec_ty _const_dicts inl))
+ -- See Note [Const rule dicts]
+ = putSrcSpanDs loc $
+ do { let poly_name = idName poly_id
; spec_name <- newLocalName poly_name
; ds_spec_expr <- dsExpr spec_expr
- ; let (bndrs, body) = collectBinders ds_spec_expr
- mb_lhs = decomposeRuleLhs (bndrs ++ const_dicts) body
-
- ; case mb_lhs of
- Nothing -> do { warnDs msg; return Nothing }
-
- Just (bndrs', var, args) -> return (Just (addInlineInfo inl spec_id spec_rhs, rule))
+ ; 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
+
+ -- 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 ->
+
+ case mb_lhs of
+ Nothing -> do { warnDs decomp_msg; return Nothing }
+
+ Just (var, args) -> return (Just (addInlineInfo inl spec_id spec_rhs, rule))
where
local_poly = setIdNotExported poly_id
-- Very important to make the 'f' non-exported,
poly_f_body = mkLams (tvs ++ dicts) $
fix_up (Let mono_bind (Var mono_id))
- -- Quantify over constant dicts on the LHS, since
- -- their value depends only on their type
- -- The ones we are interested in may even be imported
- -- e.g. GHC.Base.dEqInt
-
rule = mkLocalRule (mkFastString ("SPEC " ++ showSDoc (ppr poly_name)))
AlwaysActive poly_name
- bndrs' -- Includes constant dicts
- args
+ bndrs args
(mkVarApps (Var spec_id) bndrs)
- }
+ } }
where
-- Bind to Any any of all_ptvs that aren't
-- relevant for this particular function
(map mkArbitraryType void_tvs)
void_tvs = all_tvs \\ tvs
- msg = hang (ptext SLIT("Specialisation too complicated to desugar; ignored"))
- 2 (ppr spec_expr)
+ 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")]
+ 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)
\end{code}
+Note [Unused spec binders]
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+Consider
+ f :: a -> a
+ {-# SPECIALISE f :: Eq a => a -> a #-}
+It's true that this *is* a more specialised type, but the rule
+we get is something like this:
+ f_spec d = f
+ RULE: f = f_spec d
+Note that the rule is bogus, becuase it mentions a 'd' that is
+not bound on the LHS! But it's a silly specialisation anyway, becuase
+the constraint is unused. We could bind 'd' to (error "unused")
+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]
+~~~~~~~~~~~~~~~~~~~~~~~
+A SpecPrag has a field for "constant dicts" in the RULE, but I think
+it's pretty useless. See the place where it's generated in TcBinds.
+TcSimplify will discharge a constraint by binding it to, say,
+GHC.Base.$f2 :: Eq Int, withour putting anything in the LIE, so this
+dict won't show up in the const-dicts field. It probably doesn't matter,
+because the rule will end up being something like
+ f Int GHC.Base.$f2 = ...
+rather than
+ forall d. f Int d = ...
+The latter is more general, but in practice I think it won't make any
+difference.
+
%************************************************************************
%* *
%************************************************************************
\begin{code}
-decomposeRuleLhs :: [Var] -> CoreExpr -> Maybe ([Var], Id, [CoreExpr])
+decomposeRuleLhs :: CoreExpr -> Maybe (Id, [CoreExpr])
-- Returns Nothing if the LHS isn't of the expected shape
--- The argument 'all_bndrs' includes the "constant dicts" of the LHS,
--- and they may be GlobalIds, which we can't forall-ify.
--- So we substitute them out instead
-decomposeRuleLhs all_bndrs lhs
- = go init_env (occurAnalyseExpr lhs) -- Occurrence analysis sorts out the dict
- -- bindings so we know if they are recursive
+decomposeRuleLhs lhs
+ = go emptyVarEnv (occurAnalyseExpr lhs) -- Occurrence analysis sorts out the dict
+ -- bindings so we know if they are recursive
where
-
- -- all_bndrs may include top-level imported dicts,
- -- imported things with a for-all.
- -- So we localise them and subtitute them out
- bndr_prs = [ (id, Var (localise id)) | id <- all_bndrs, isGlobalId id ]
- localise d = mkLocalId (idName d) (idType d)
-
- init_env = mkVarEnv bndr_prs
- all_bndrs' = map subst_bndr all_bndrs
- subst_bndr bndr = case lookupVarEnv init_env bndr of
- Just (Var bndr') -> bndr'
- Just other -> panic "decomposeRuleLhs"
- Nothing -> bndr
-
-- 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
= go (extendVarEnv env dict (simpleSubst env rhs)) body
go env body
= case collectArgs (simpleSubst env body) of
- (Var fn, args) -> Just (all_bndrs', fn, args)
+ (Var fn, args) -> Just (fn, args)
other -> Nothing
simpleSubst :: IdEnv CoreExpr -> CoreExpr -> CoreExpr
-- (a) takes no account of capture; dictionary bindings use new names
-- (b) can have a GlobalId (imported) in its domain
-- (c) Ids only; no types are substituted
-
+--
+-- (b) is the reason we can't use CoreSubst... and it's no longer relevant
+-- so really we should replace simpleSubst
simpleSubst subst expr
= go expr
where
go (Case scrut bndr ty alts) = Case (go scrut) bndr ty
[(c,bs,go r) | (c,bs,r) <- alts]
-addInlinePrags :: [Prag] -> Id -> CoreExpr -> (Id,CoreExpr)
+addInlinePrags :: [LPrag] -> Id -> CoreExpr -> (Id,CoreExpr)
addInlinePrags prags bndr rhs
- = case [inl | InlinePrag inl <- prags] of
+ = case [inl | L _ (InlinePrag inl) <- prags] of
[] -> (bndr, rhs)
(inl:_) -> addInlineInfo inl bndr rhs
projects / ghc-hetmet.git / commitdiff