Desugaring exporessions.
\begin{code}
-{-# OPTIONS -w #-}
+{-# OPTIONS -fno-warn-incomplete-patterns #-}
-- 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
#include "HsVersions.h"
-
import Match
import MatchLit
import DsBinds
import Type
import CoreSyn
import CoreUtils
+import MkCore
+import DynFlags
import CostCentre
import Id
import PrelInfo
dsValBinds (ValBindsOut binds _) body = foldrM ds_val_bind body binds
-------------------------
+dsIPBinds :: HsIPBinds Id -> CoreExpr -> DsM CoreExpr
dsIPBinds (IPBinds ip_binds dict_binds) body
= do { prs <- dsLHsBinds dict_binds
; let inner = Let (Rec prs) body
; result <- matchEquations PatBindRhs [var] [eqn] (exprType body)
; return (scrungleMatch var rhs result) }
- other -> pprPanic "dsLet: unlifted" (pprLHsBinds hsbinds $$ ppr body)
+ _ -> pprPanic "dsLet: unlifted" (pprLHsBinds hsbinds $$ ppr body)
-- Ordinary case for bindings; none should be unlifted
-ds_val_bind (is_rec, binds) body
+ds_val_bind (_is_rec, binds) body
= do { prs <- dsLHsBinds binds
; ASSERT( not (any (isUnLiftedType . idType . fst) prs) )
case prs of
- [] -> return body
- other -> return (Let (Rec prs) body) }
+ [] -> return body
+ _ -> return (Let (Rec prs) body) }
-- Use a Rec regardless of is_rec.
-- Why? Because it allows the binds to be all
-- mixed up, which is what happens in one rare case
isUnboxedTupleBind :: HsBind Id -> Bool
isUnboxedTupleBind (PatBind { pat_rhs_ty = ty }) = isUnboxedTupleType ty
-isUnboxedTupleBind other = False
+isUnboxedTupleBind _ = False
scrungleMatch :: Id -> CoreExpr -> CoreExpr -> CoreExpr
-- Returns something like (let var = scrut in body)
dsExpr (NegApp expr neg_expr)
= App <$> dsExpr neg_expr <*> dsLExpr expr
-dsExpr expr@(HsLam a_Match)
+dsExpr (HsLam a_Match)
= uncurry mkLams <$> matchWrapper LambdaExpr a_Match
-dsExpr expr@(HsApp fun arg)
- = mkDsApp <$> dsLExpr fun <*> dsLExpr arg
+dsExpr (HsApp fun arg)
+ = mkCoreApp <$> dsLExpr fun <*> dsLExpr arg
\end{code}
Operator sections. At first it looks as if we can convert
\begin{code}
dsExpr (OpApp e1 op _ e2)
= -- for the type of y, we need the type of op's 2nd argument
- mkDsApps <$> dsLExpr op <*> mapM dsLExpr [e1, e2]
+ mkCoreApps <$> dsLExpr op <*> mapM dsLExpr [e1, e2]
dsExpr (SectionL expr op) -- Desugar (e !) to ((!) e)
- = mkDsApp <$> dsLExpr op <*> dsLExpr expr
+ = mkCoreApp <$> dsLExpr op <*> dsLExpr expr
-- dsLExpr (SectionR op expr) -- \ x -> op x expr
dsExpr (SectionR op expr) = do
x_id <- newSysLocalDs x_ty
y_id <- newSysLocalDs y_ty
return (bindNonRec y_id y_core $
- Lam x_id (mkDsApps core_op [Var x_id, Var y_id]))
+ Lam x_id (mkCoreApps core_op [Var x_id, Var y_id]))
dsExpr (HsSCC cc expr) = do
mod_name <- getModuleDs
dsExpr (HsCoreAnn fs expr)
= Note (CoreNote $ unpackFS fs) <$> dsLExpr expr
-dsExpr (HsCase discrim matches) = do
- core_discrim <- dsLExpr discrim
- ([discrim_var], matching_code) <- matchWrapper CaseAlt matches
- return (scrungleMatch discrim_var core_discrim matching_code)
+dsExpr (HsCase discrim matches@(MatchGroup _ rhs_ty))
+ | isEmptyMatchGroup matches -- A Core 'case' is always non-empty
+ = -- So desugar empty HsCase to error call
+ mkErrorAppDs pAT_ERROR_ID (funResultTy rhs_ty) "case"
+
+ | otherwise
+ = do { core_discrim <- dsLExpr discrim
+ ; ([discrim_var], matching_code) <- matchWrapper CaseAlt matches
+ ; return (scrungleMatch discrim_var core_discrim matching_code) }
-- Pepe: The binds are in scope in the body but NOT in the binding group
-- This is to avoid silliness in breakpoints
\underline{\bf Various data construction things}
% ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
\begin{code}
-dsExpr (ExplicitList ty xs)
- = go xs
- where
- go [] = return (mkNilExpr ty)
- go (x:xs) = mkConsExpr ty <$> dsLExpr x <*> go xs
+dsExpr (ExplicitList elt_ty xs)
+ = dsExplicitList elt_ty xs
-- we create a list from the array elements and convert them into a list using
-- `PrelPArr.toP'
dsExpr (PArrSeq expr (FromThenTo from thn to))
= mkApps <$> dsExpr expr <*> mapM dsLExpr [from, thn, to]
-dsExpr (PArrSeq expr _)
+dsExpr (PArrSeq _ _)
= panic "DsExpr.dsExpr: Infinite parallel array!"
-- the parser shouldn't have generated it and the renamer and typechecker
-- shouldn't have let it through
\begin{code}
-#ifdef DEBUG
-- HsSyn constructs that just shouldn't be here:
dsExpr (ExprWithTySig _ _) = panic "dsExpr:ExprWithTySig"
-#endif
findField :: [HsRecField Id arg] -> Name -> [arg]
%--------------------------------------------------------------------
+Note [Desugaring explicit lists]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Explicit lists are desugared in a cleverer way to prevent some
+fruitless allocations. Essentially, whenever we see a list literal
+[x_1, ..., x_n] we:
+
+1. Find the tail of the list that can be allocated statically (say
+ [x_k, ..., x_n]) by later stages and ensure we desugar that
+ normally: this makes sure that we don't cause a code size increase
+ by having the cons in that expression fused (see later) and hence
+ being unable to statically allocate any more
+
+2. For the prefix of the list which cannot be allocated statically,
+ say [x_1, ..., x_(k-1)], we turn it into an expression involving
+ build so that if we find any foldrs over it it will fuse away
+ entirely!
+
+ So in this example we will desugar to:
+ build (\c n -> x_1 `c` x_2 `c` .... `c` foldr c n [x_k, ..., x_n]
+
+ If fusion fails to occur then build will get inlined and (since we
+ defined a RULE for foldr (:) []) we will get back exactly the
+ normal desugaring for an explicit list.
+
+This optimisation can be worth a lot: up to 25% of the total
+allocation in some nofib programs. Specifically
+
+ Program Size Allocs Runtime CompTime
+ rewrite +0.0% -26.3% 0.02 -1.8%
+ ansi -0.3% -13.8% 0.00 +0.0%
+ lift +0.0% -8.7% 0.00 -2.3%
+
+Of course, if rules aren't turned on then there is pretty much no
+point doing this fancy stuff, and it may even be harmful.
+\begin{code}
+
+dsExplicitList :: PostTcType -> [LHsExpr Id] -> DsM CoreExpr
+-- See Note [Desugaring explicit lists]
+dsExplicitList elt_ty xs = do
+ dflags <- getDOptsDs
+ xs' <- mapM dsLExpr xs
+ if not (dopt Opt_RewriteRules dflags)
+ then return $ mkListExpr elt_ty xs'
+ else mkBuildExpr elt_ty (mkSplitExplicitList (thisPackage dflags) xs')
+ where
+ mkSplitExplicitList this_package xs' (c, _) (n, n_ty) = do
+ let (dynamic_prefix, static_suffix) = spanTail (rhsIsStatic this_package) xs'
+ static_suffix' = mkListExpr elt_ty static_suffix
+
+ folded_static_suffix <- mkFoldrExpr elt_ty n_ty (Var c) (Var n) static_suffix'
+ let build_body = foldr (App . App (Var c)) folded_static_suffix dynamic_prefix
+ return build_body
+
+spanTail :: (a -> Bool) -> [a] -> ([a], [a])
+spanTail f xs = (reverse rejected, reverse satisfying)
+ where (satisfying, rejected) = span f $ reverse xs
+\end{code}
+
Desugar 'do' and 'mdo' expressions (NOT list comprehensions, they're
handled in DsListComp). Basically does the translation given in the
Haskell 98 report:
-> Type -- Type of the whole expression
-> DsM CoreExpr
-dsDo stmts body result_ty
+dsDo stmts body _result_ty
= go (map unLoc stmts)
where
go [] = dsLExpr body
go (BindStmt pat rhs bind_op fail_op : stmts)
=
- do { body <- go stmts
+ do { body <- go stmts
+ ; rhs' <- dsLExpr rhs
+ ; bind_op' <- dsExpr bind_op
; var <- selectSimpleMatchVarL pat
+ ; let bind_ty = exprType bind_op' -- rhs -> (pat -> res1) -> res2
+ res1_ty = funResultTy (funArgTy (funResultTy bind_ty))
; match <- matchSinglePat (Var var) (StmtCtxt DoExpr) pat
- result_ty (cantFailMatchResult body)
+ res1_ty (cantFailMatchResult body)
; match_code <- handle_failure pat match fail_op
- ; rhs' <- dsLExpr rhs
- ; bind_op' <- dsExpr bind_op
; return (mkApps bind_op' [rhs', Lam var match_code]) }
-- In a do expression, pattern-match failure just calls
| otherwise
= extractMatchResult match (error "It can't fail")
+mk_fail_msg :: Located e -> String
mk_fail_msg pat = "Pattern match failure in do expression at " ++
showSDoc (ppr (getLoc pat))
\end{code}
projects / ghc-hetmet.git / blobdiff