This module exports some utility functions of no great interest.
\begin{code}
-
-- | Utility functions for constructing Core syntax, principally for desugaring
module DsUtils (
EquationInfo(..),
mkCoPrimCaseMatchResult, mkCoAlgCaseMatchResult,
wrapBind, wrapBinds,
- mkErrorAppDs,
+ mkErrorAppDs, mkCoreAppDs, mkCoreAppsDs,
seqVar,
-- LHs tuples
- mkLHsVarTup, mkLHsTup, mkLHsVarPatTup, mkLHsPatTup,
+ mkLHsVarPatTup, mkLHsPatTup, mkVanillaTuplePat,
mkBigLHsVarTup, mkBigLHsTup, mkBigLHsVarPatTup, mkBigLHsPatTup,
mkSelectorBinds,
import ListSetOps
import FastString
import StaticFlags
-
-import Data.Char
\end{code}
selectMatchVars ps = mapM selectMatchVar ps
selectMatchVar :: Pat Id -> DsM Id
-selectMatchVar (BangPat pat) = selectMatchVar (unLoc pat)
-selectMatchVar (LazyPat pat) = selectMatchVar (unLoc pat)
-selectMatchVar (ParPat pat) = selectMatchVar (unLoc pat)
-selectMatchVar (VarPat var) = return var
+selectMatchVar (BangPat pat) = selectMatchVar (unLoc pat)
+selectMatchVar (LazyPat pat) = selectMatchVar (unLoc pat)
+selectMatchVar (ParPat pat) = selectMatchVar (unLoc pat)
+selectMatchVar (VarPat var) = return (localiseId var) -- Note [Localise pattern binders]
selectMatchVar (AsPat var _) = return (unLoc var)
-selectMatchVar other_pat = newSysLocalDs (hsPatType other_pat)
+selectMatchVar other_pat = newSysLocalDs (hsPatType other_pat)
-- OK, better make up one...
\end{code}
+Note [Localise pattern binders]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Consider module M where
+ [Just a] = e
+After renaming it looks like
+ module M where
+ [Just M.a] = e
+
+We don't generalise, since it's a pattern binding, monomorphic, etc,
+so after desugaring we may get something like
+ M.a = case e of (v:_) ->
+ case v of Just M.a -> M.a
+Notice the "M.a" in the pattern; after all, it was in the original
+pattern. However, after optimisation those pattern binders can become
+let-binders, and then end up floated to top level. They have a
+different *unique* by then (the simplifier is good about maintaining
+proper scoping), but it's BAD to have two top-level bindings with the
+External Name M.a, because that turns into two linker symbols for M.a.
+It's quite rare for this to actually *happen* -- the only case I know
+of is tc003 compiled with the 'hpc' way -- but that only makes it
+all the more annoying.
+
+To avoid this, we craftily call 'localiseId' in the desugarer, which
+simply turns the External Name for the Id into an Internal one, but
+doesn't change the unique. So the desugarer produces this:
+ M.a{r8} = case e of (v:_) ->
+ case v of Just a{r8} -> M.a{r8}
+The unique is still 'r8', but the binding site in the pattern
+is now an Internal Name. Now the simplifier's usual mechanisms
+will propagate that Name to all the occurrence sites, as well as
+un-shadowing it, so we'll get
+ M.a{r8} = case e of (v:_) ->
+ case v of Just a{s77} -> a{s77}
+In fact, even CoreSubst.simplOptExpr will do this, and simpleOptExpr
+runs on the output of the desugarer, so all is well by the end of
+the desugaring pass.
+
%************************************************************************
%* *
wrapBind :: Var -> Var -> CoreExpr -> CoreExpr
wrapBind new old body -- Can deal with term variables *or* type variables
| new==old = body
- | isTyVar new = Let (mkTyBind new (mkTyVarTy old)) body
+ | isTyCoVar new = Let (mkTyBind new (mkTyVarTy old)) body
| otherwise = Let (NonRec new (Var old)) body
seqVar :: Var -> CoreExpr -> CoreExpr
-- let var' = viewExpr var in mr
mkViewMatchResult :: Id -> CoreExpr -> Id -> MatchResult -> MatchResult
mkViewMatchResult var' viewExpr var =
- adjustMatchResult (mkCoreLet (NonRec var' (mkCoreApp viewExpr (Var var))))
+ adjustMatchResult (mkCoreLet (NonRec var' (mkCoreAppDs viewExpr (Var var))))
mkEvalMatchResult :: Id -> Type -> MatchResult -> MatchResult
mkEvalMatchResult var ty
| otherwise
= CanFail
- wild_var = mkWildId (idType var)
sorted_alts = sortWith get_tag match_alts
get_tag (con, _, _) = dataConTag con
mk_case fail = do alts <- mapM (mk_alt fail) sorted_alts
- return (Case (Var var) wild_var ty (mk_default fail ++ alts))
+ return (mkWildCase (Var var) (idType var) ty (mk_default fail ++ alts))
mk_alt fail (con, args, MatchResult _ body_fn) = do
body <- body_fn fail
isPArrFakeAlts [] = panic "DsUtils: unexpectedly found an empty list of PArr fake alternatives"
--
mk_parrCase fail = do
- lengthP <- dsLookupGlobalId lengthPName
+ lengthP <- dsLookupDPHId lengthPName
alt <- unboxAlt
- return (Case (len lengthP) (mkWildId intTy) ty [alt])
+ return (mkWildCase (len lengthP) intTy ty [alt])
where
elemTy = case splitTyConApp (idType var) of
(_, [elemTy]) -> elemTy
--
unboxAlt = do
l <- newSysLocalDs intPrimTy
- indexP <- dsLookupGlobalId indexPName
+ indexP <- dsLookupDPHId indexPName
alts <- mapM (mkAlt indexP) sorted_alts
- return (DataAlt intDataCon, [l], (Case (Var l) wild ty (dft : alts)))
+ return (DataAlt intDataCon, [l], mkWildCase (Var l) intPrimTy ty (dft : alts))
where
- wild = mkWildId intPrimTy
dft = (DEFAULT, [], fail)
--
-- each alternative matches one array length (corresponding to one
\begin{code}
mkErrorAppDs :: Id -- The error function
-> Type -- Type to which it should be applied
- -> String -- The error message string to pass
+ -> SDoc -- The error message string to pass
-> DsM CoreExpr
mkErrorAppDs err_id ty msg = do
src_loc <- getSrcSpanDs
let
- full_msg = showSDoc (hcat [ppr src_loc, text "|", text msg])
+ full_msg = showSDoc (hcat [ppr src_loc, text "|", msg])
core_msg = Lit (mkMachString full_msg)
-- mkMachString returns a result of type String#
return (mkApps (Var err_id) [Type ty, core_msg])
\end{code}
+'mkCoreAppDs' and 'mkCoreAppsDs' hand the special-case desugaring of 'seq'.
+
+Note [Desugaring seq (1)] cf Trac #1031
+~~~~~~~~~~~~~~~~~~~~~~~~~
+ f x y = x `seq` (y `seq` (# x,y #))
+
+The [CoreSyn let/app invariant] means that, other things being equal, because
+the argument to the outer 'seq' has an unlifted type, we'll use call-by-value thus:
+
+ f x y = case (y `seq` (# x,y #)) of v -> x `seq` v
+
+But that is bad for two reasons:
+ (a) we now evaluate y before x, and
+ (b) we can't bind v to an unboxed pair
+
+Seq is very, very special! So we recognise it right here, and desugar to
+ case x of _ -> case y of _ -> (# x,y #)
+
+Note [Desugaring seq (2)] cf Trac #2273
+~~~~~~~~~~~~~~~~~~~~~~~~~
+Consider
+ let chp = case b of { True -> fst x; False -> 0 }
+ in chp `seq` ...chp...
+Here the seq is designed to plug the space leak of retaining (snd x)
+for too long.
+
+If we rely on the ordinary inlining of seq, we'll get
+ let chp = case b of { True -> fst x; False -> 0 }
+ case chp of _ { I# -> ...chp... }
+
+But since chp is cheap, and the case is an alluring contet, we'll
+inline chp into the case scrutinee. Now there is only one use of chp,
+so we'll inline a second copy. Alas, we've now ruined the purpose of
+the seq, by re-introducing the space leak:
+ case (case b of {True -> fst x; False -> 0}) of
+ I# _ -> ...case b of {True -> fst x; False -> 0}...
+
+We can try to avoid doing this by ensuring that the binder-swap in the
+case happens, so we get his at an early stage:
+ case chp of chp2 { I# -> ...chp2... }
+But this is fragile. The real culprit is the source program. Perhaps we
+should have said explicitly
+ let !chp2 = chp in ...chp2...
+
+But that's painful. So the code here does a little hack to make seq
+more robust: a saturated application of 'seq' is turned *directly* into
+the case expression, thus:
+ x `seq` e2 ==> case x of x -> e2 -- Note shadowing!
+ e1 `seq` e2 ==> case x of _ -> e2
+
+So we desugar our example to:
+ let chp = case b of { True -> fst x; False -> 0 }
+ case chp of chp { I# -> ...chp... }
+And now all is well.
+
+The reason it's a hack is because if you define mySeq=seq, the hack
+won't work on mySeq.
+
+Note [Desugaring seq (3)] cf Trac #2409
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The isLocalId ensures that we don't turn
+ True `seq` e
+into
+ case True of True { ... }
+which stupidly tries to bind the datacon 'True'.
+
+\begin{code}
+mkCoreAppDs :: CoreExpr -> CoreExpr -> CoreExpr
+mkCoreAppDs (Var f `App` Type ty1 `App` Type ty2 `App` arg1) arg2
+ | f `hasKey` seqIdKey -- Note [Desugaring seq (1), (2)]
+ = Case arg1 case_bndr ty2 [(DEFAULT,[],arg2)]
+ where
+ case_bndr = case arg1 of
+ Var v1 | isLocalId v1 -> v1 -- Note [Desugaring seq (2) and (3)]
+ _ -> mkWildValBinder ty1
+
+mkCoreAppDs fun arg = mkCoreApp fun arg -- The rest is done in MkCore
+
+mkCoreAppsDs :: CoreExpr -> [CoreExpr] -> CoreExpr
+mkCoreAppsDs fun args = foldl mkCoreAppDs fun args
+\end{code}
+
+
%************************************************************************
%* *
\subsection[mkSelectorBind]{Make a selector bind}
-- For the error message we make one error-app, to avoid duplication.
-- But we need it at different types... so we use coerce for that
- err_expr <- mkErrorAppDs iRREFUT_PAT_ERROR_ID unitTy (showSDoc (ppr pat))
+ err_expr <- mkErrorAppDs iRREFUT_PAT_ERROR_ID unitTy (ppr pat)
err_var <- newSysLocalDs unitTy
binds <- mapM (mk_bind val_var err_var) binders
return ( (val_var, val_expr) :
| otherwise = do
- error_expr <- mkErrorAppDs iRREFUT_PAT_ERROR_ID tuple_ty (showSDoc (ppr pat))
+ error_expr <- mkErrorAppDs iRREFUT_PAT_ERROR_ID tuple_ty (ppr pat)
tuple_expr <- matchSimply val_expr PatBindRhs pat local_tuple error_expr
tuple_var <- newSysLocalDs tuple_ty
- let
- mk_tup_bind binder
- = (binder, mkTupleSelector binders binder tuple_var (Var tuple_var))
+ let mk_tup_bind binder
+ = (binder, mkTupleSelector local_binders binder tuple_var (Var tuple_var))
return ( (tuple_var, tuple_expr) : map mk_tup_bind binders )
where
- binders = collectPatBinders pat
- local_tuple = mkBigCoreVarTup binders
- tuple_ty = exprType local_tuple
+ binders = collectPatBinders pat
+ local_binders = map localiseId binders -- See Note [Localise pattern binders]
+ local_tuple = mkBigCoreVarTup binders
+ tuple_ty = exprType local_tuple
mk_bind scrut_var err_var bndr_var = do
-- (mk_bind sv err_var) generates
\end{code}
-Creating tuples and their types for full Haskell expressions
+Creating big tuples and their types for full Haskell expressions.
+They work over *Ids*, and create tuples replete with their types,
+which is whey they are not in HsUtils.
\begin{code}
-
--- Smart constructors for source tuple expressions
-mkLHsVarTup :: [Id] -> LHsExpr Id
-mkLHsVarTup ids = mkLHsTup (map nlHsVar ids)
-
-mkLHsTup :: [LHsExpr Id] -> LHsExpr Id
-mkLHsTup [] = nlHsVar unitDataConId
-mkLHsTup [lexp] = lexp
-mkLHsTup lexps = L (getLoc (head lexps)) $
- ExplicitTuple lexps Boxed
-
--- Smart constructors for source tuple patterns
-mkLHsVarPatTup :: [Id] -> LPat Id
-mkLHsVarPatTup bs = mkLHsPatTup (map nlVarPat bs)
-
mkLHsPatTup :: [LPat Id] -> LPat Id
mkLHsPatTup [] = noLoc $ mkVanillaTuplePat [] Boxed
mkLHsPatTup [lpat] = lpat
mkLHsPatTup lpats = L (getLoc (head lpats)) $
mkVanillaTuplePat lpats Boxed
+mkLHsVarPatTup :: [Id] -> LPat Id
+mkLHsVarPatTup bs = mkLHsPatTup (map nlVarPat bs)
+
+mkVanillaTuplePat :: [OutPat Id] -> Boxity -> Pat Id
+-- A vanilla tuple pattern simply gets its type from its sub-patterns
+mkVanillaTuplePat pats box
+ = TuplePat pats box (mkTupleTy box (map hsLPatType pats))
+
-- The Big equivalents for the source tuple expressions
mkBigLHsVarTup :: [Id] -> LHsExpr Id
mkBigLHsVarTup ids = mkBigLHsTup (map nlHsVar ids)
mkBigLHsTup :: [LHsExpr Id] -> LHsExpr Id
-mkBigLHsTup = mkChunkified mkLHsTup
-
+mkBigLHsTup = mkChunkified mkLHsTupleExpr
-- The Big equivalents for the source tuple patterns
mkBigLHsVarPatTup :: [Id] -> LPat Id
\begin{code}
mkFailurePair :: CoreExpr -- Result type of the whole case expression
-> DsM (CoreBind, -- Binds the newly-created fail variable
- -- to either the expression or \ _ -> expression
- CoreExpr) -- Either the fail variable, or fail variable
- -- applied to unit tuple
+ -- to \ _ -> expression
+ CoreExpr) -- Fail variable applied to realWorld#
+-- See Note [Failure thunks and CPR]
mkFailurePair expr
- | isUnLiftedType ty = do
- fail_fun_var <- newFailLocalDs (unitTy `mkFunTy` ty)
- fail_fun_arg <- newSysLocalDs unitTy
- return (NonRec fail_fun_var (Lam fail_fun_arg expr),
- App (Var fail_fun_var) (Var unitDataConId))
-
- | otherwise = do
- fail_var <- newFailLocalDs ty
- return (NonRec fail_var expr, Var fail_var)
+ = do { fail_fun_var <- newFailLocalDs (realWorldStatePrimTy `mkFunTy` ty)
+ ; fail_fun_arg <- newSysLocalDs realWorldStatePrimTy
+ ; return (NonRec fail_fun_var (Lam fail_fun_arg expr),
+ App (Var fail_fun_var) (Var realWorldPrimId)) }
where
ty = exprType expr
\end{code}
+Note [Failure thunks and CPR]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+When we make a failure point we ensure that it
+does not look like a thunk. Example:
+
+ let fail = \rw -> error "urk"
+ in case x of
+ [] -> fail realWorld#
+ (y:ys) -> case ys of
+ [] -> fail realWorld#
+ (z:zs) -> (y,z)
+
+Reason: we know that a failure point is always a "join point" and is
+entered at most once. Adding a dummy 'realWorld' token argument makes
+it clear that sharing is not an issue. And that in turn makes it more
+CPR-friendly. This matters a lot: if you don't get it right, you lose
+the tail call property. For example, see Trac #3403.
+
\begin{code}
mkOptTickBox :: Maybe (Int,[Id]) -> CoreExpr -> DsM CoreExpr
mkOptTickBox Nothing e = return e
projects / ghc-hetmet.git / blobdiff