#include "HsVersions.h"
-import CmdLineOpts ( DynFlags, DynFlag(..), dopt, opt_LiberateCaseThreshold )
+import DynFlags ( DynFlags, DynFlag(..) )
+import StaticFlags ( opt_LiberateCaseThreshold )
import CoreLint ( showPass, endPass )
import CoreSyn
import CoreUnfold ( couldBeSmallEnoughToInline )
-import Var ( Id )
+import Id ( Id, setIdName, idName, setIdNotExported )
import VarEnv
-import Maybes
+import Name ( localiseName )
+import Outputable
+import Util ( notNull )
\end{code}
This module walks over @Core@, and looks for @case@ on free variables.
\end{verbatim}
(note the NEED for shadowing)
-=> Run Andr\'e's wonder pass ...
+=> Simplify
+
\begin{verbatim}
f = \ t -> case v of
V a b -> a : (letrec
f = \ t -> a : f t
in f t)
\begin{verbatim}
+
Better code, because 'a' is free inside the inner letrec, rather
than needing projection from v.
-- (top-level and imported things have
-- a level of zero)
- (IdEnv CoreBind)-- Binds *only* recursively defined
+ (IdEnv CoreBind) -- Binds *only* recursively defined
-- Ids, to their own binding group,
-- and *only* in their own RHSs
= do {
showPass dflags "Liberate case" ;
let { binds' = do_prog (initEnv opt_LiberateCaseThreshold) binds } ;
- endPass dflags "Liberate case"
- (dopt Opt_D_verbose_core2core dflags)
+ endPass dflags "Liberate case" Opt_D_verbose_core2core binds'
{- no specific flag for dumping -}
- binds'
}
where
do_prog env [] = []
-- We extend the rec-env by binding each Id to its rhs, first
-- processing the rhs with an *un-extended* environment, so
-- that the same process doesn't occur for ever!
-
- extended_env
- = addRecBinds env [ (binder, libCase env_body rhs)
- | (binder, rhs) <- pairs ]
-
- -- Why "localiseId" above? Because we're creating a new local
- -- copy of the original binding. In particular, the original
- -- binding might have been for a top-level, and this copy clearly
- -- will not be top-level!
-
- -- It is enough to change just the binder, because subsequent
- -- simplification will propagate the right info from the binder.
-
- -- Why does it matter? Because the codeGen keeps a separate
- -- environment for top-level Ids, and it is disastrous for it
- -- to think that something is top-level when it isn't.
--
- -- [May 98: all this is now handled by SimplCore.tidyCore]
+ extended_env = addRecBinds env [ (adjust binder, libCase env_body rhs)
+ | (binder, rhs) <- pairs ]
+
+ -- Two subtle things:
+ -- (a) Reset the export flags on the binders so
+ -- that we don't get name clashes on exported things if the
+ -- local binding floats out to top level. This is most unlikely
+ -- to happen, since the whole point concerns free variables.
+ -- But resetting the export flag is right regardless.
+ --
+ -- (b) Make the name an Internal one. External Names should never be
+ -- nested; if it were floated to the top level, we'd get a name
+ -- clash at code generation time.
+ adjust bndr = setIdNotExported (setIdName bndr (localiseName (idName bndr)))
rhs_small_enough rhs = couldBeSmallEnoughToInline lIBERATE_BOMB_SIZE rhs
-
- lIBERATE_BOMB_SIZE = bombOutSize env
+ lIBERATE_BOMB_SIZE = bombOutSize env
\end{code}
where
(env_body, bind') = libCaseBind env bind
-libCase env (Case scrut bndr alts)
- = Case (libCase env scrut) bndr (map (libCaseAlt env_alts) alts)
+libCase env (Case scrut bndr ty alts)
+ = Case (libCase env scrut) bndr ty (map (libCaseAlt env_alts) alts)
where
env_alts = addBinders env_with_scrut [bndr]
env_with_scrut = case scrut of
\begin{code}
libCaseId :: LibCaseEnv -> Id -> CoreExpr
libCaseId env v
- | maybeToBool maybe_rec_bind && -- It's a use of a recursive thing
- there_are_free_scruts -- with free vars scrutinised in RHS
+ | Just the_bind <- lookupRecId env v -- It's a use of a recursive thing
+ , notNull free_scruts -- with free vars scrutinised in RHS
= Let the_bind (Var v)
| otherwise
= Var v
where
- maybe_rec_bind :: Maybe CoreBind -- The binding of the recursive thingy
- maybe_rec_bind = lookupRecId env v
- Just the_bind = maybe_rec_bind
-
rec_id_level = lookupLevel env v
-
- there_are_free_scruts = freeScruts env rec_id_level
+ free_scruts = freeScruts env rec_id_level
\end{code}
lookupRecId :: LibCaseEnv -> Id -> Maybe CoreBind
lookupRecId (LibCaseEnv bomb lvl lvl_env rec_env scruts) id
-#ifndef DEBUG
= lookupVarEnv rec_env id
-#else
- = case (lookupVarEnv rec_env id) of
- xxx@(Just _) -> xxx
- xxx -> xxx
-#endif
lookupLevel :: LibCaseEnv -> Id -> LibCaseLevel
lookupLevel (LibCaseEnv bomb lvl lvl_env rec_env scruts) id
freeScruts :: LibCaseEnv
-> LibCaseLevel -- Level of the recursive Id
- -> Bool -- True <=> there is an enclosing case of a variable
- -- bound outside (ie level <=) the recursive Id.
+ -> [Id] -- Ids that are scrutinised between the binding
+ -- of the recursive Id and here
freeScruts (LibCaseEnv bomb lvl lvl_env rec_env scruts) rec_bind_lvl
- = not (null free_scruts)
- where
- free_scruts = [v | (v,lvl) <- scruts, lvl > rec_bind_lvl]
+ = [v | (v,scrut_lvl) <- scruts, scrut_lvl > rec_bind_lvl]
\end{code}
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