-- Standard modules
import Debug.Trace
import qualified Maybe
+import qualified List
import qualified "transformers" Control.Monad.Trans as Trans
import qualified Control.Monad as Monad
import qualified Control.Monad.Trans.Writer as Writer
import qualified CoreUtils
import qualified Type
import qualified TcType
+import qualified Name
import qualified Id
import qualified Var
import qualified VarSet
-- Generate a binder for the expression
id <- Trans.lift $ mkBinderFor val "castval"
-- Extract the expression
- change $ Let (Rec [(id, val)]) (Cast (Var id) ty)
+ change $ Let (NonRec id val) (Cast (Var id) ty)
else
return expr
-- Leave all other expressions unchanged
-- Perform this transform everywhere
castsimpltop = everywhere ("castsimpl", castsimpl)
+
+--------------------------------
+-- Lambda simplication
+--------------------------------
+-- Ensure that a lambda always evaluates to a let expressions or a simple
+-- variable reference.
+lambdasimpl, lambdasimpltop :: Transform
+-- Don't simplify a lambda that evaluates to let, since this is already
+-- normal form (and would cause infinite loops).
+lambdasimpl expr@(Lam _ (Let _ _)) = return expr
+-- Put the of a lambda in its own binding, but not when the expression is
+-- already a local variable, or not representable (to prevent loops with
+-- inlinenonrep).
+lambdasimpl expr@(Lam bndr res) = do
+ repr <- isRepr res
+ local_var <- Trans.lift $ is_local_var res
+ if not local_var && repr
+ then do
+ id <- Trans.lift $ mkBinderFor res "res"
+ change $ Lam bndr (Let (NonRec id res) (Var id))
+ else
+ -- If the result is already a local var or not representable, don't
+ -- extract it.
+ return expr
+
+-- Leave all other expressions unchanged
+lambdasimpl expr = return expr
+-- Perform this transform everywhere
+lambdasimpltop = everywhere ("lambdasimpl", lambdasimpl)
+
--------------------------------
--- let recursification
+-- let derecursification
--------------------------------
-letrec, letrectop :: Transform
-letrec (Let (NonRec b expr) res) = change $ Let (Rec [(b, expr)]) res
+letderec, letderectop :: Transform
+letderec expr@(Let (Rec binds) res) = case liftable of
+ -- Nothing is liftable, just return
+ [] -> return expr
+ -- Something can be lifted, generate a new let expression
+ _ -> change $ mkNonRecLets liftable (Let (Rec nonliftable) res)
+ where
+ -- Make a list of all the binders bound in this recursive let
+ bndrs = map fst binds
+ -- See which bindings are liftable
+ (liftable, nonliftable) = List.partition canlift binds
+ -- Any expression that does not use any of the binders in this recursive let
+ -- can be lifted into a nonrec let. It can't use its own binder either,
+ -- since that would mean the binding is self-recursive and should be in a
+ -- single bind recursive let.
+ canlift (bndr, e) = not $ expr_uses_binders bndrs e
-- Leave all other expressions unchanged
-letrec expr = return expr
+letderec expr = return expr
-- Perform this transform everywhere
-letrectop = everywhere ("letrec", letrec)
+letderectop = everywhere ("letderec", letderec)
--------------------------------
-- let simplification
--------------------------------
letsimpl, letsimpltop :: Transform
+-- Don't simplify a let that evaluates to another let, since this is already
+-- normal form (and would cause infinite loops with letflat below).
+letsimpl expr@(Let _ (Let _ _)) = return expr
-- Put the "in ..." value of a let in its own binding, but not when the
-- expression is already a local variable, or not representable (to prevent loops with inlinenonrep).
-letsimpl expr@(Let (Rec binds) res) = do
+letsimpl expr@(Let binds res) = do
repr <- isRepr res
local_var <- Trans.lift $ is_local_var res
if not local_var && repr
-- If the result is not a local var already (to prevent loops with
-- ourselves), extract it.
id <- Trans.lift $ mkBinderFor res "foo"
- let bind = (id, res)
- change $ Let (Rec (bind:binds)) (Var id)
+ change $ Let binds (Let (NonRec id res) (Var id))
else
-- If the result is already a local var, don't extract it.
return expr
--------------------------------
-- let flattening
--------------------------------
+-- Takes a let that binds another let, and turns that into two nested lets.
+-- e.g., from:
+-- let b = (let b' = expr' in res') in res
+-- to:
+-- let b' = expr' in (let b = res' in res)
letflat, letflattop :: Transform
+-- Turn a nonrec let that binds a let into two nested lets.
+letflat (Let (NonRec b (Let binds res')) res) =
+ change $ Let binds (Let (NonRec b res') res)
letflat (Let (Rec binds) expr) = do
- -- Turn each binding into a list of bindings (possibly containing just one
- -- element, of course)
- bindss <- Monad.mapM flatbind binds
- -- Concat all the bindings
- let binds' = concat bindss
+ -- Flatten each binding.
+ binds' <- Utils.concatM $ Monad.mapM flatbind binds
-- Return the new let. We don't use change here, since possibly nothing has
-- changed. If anything has changed, flatbind has already flagged that
-- change.
-- into a list with just that binding
flatbind :: (CoreBndr, CoreExpr) -> TransformMonad [(CoreBndr, CoreExpr)]
flatbind (b, Let (Rec binds) expr) = change ((b, expr):binds)
+ flatbind (b, Let (NonRec b' expr') expr) = change [(b, expr), (b', expr')]
flatbind (b, expr) = return [(b, expr)]
-- Leave all other expressions unchanged
letflat expr = return expr
-- Perform this transform everywhere
letflattop = everywhere ("letflat", letflat)
+--------------------------------
+-- empty let removal
+--------------------------------
+-- Remove empty (recursive) lets
+letremove, letremovetop :: Transform
+letremove (Let (Rec []) res) = change $ res
+-- Leave all other expressions unchanged
+letremove expr = return expr
+-- Perform this transform everywhere
+letremovetop = everywhere ("letremove", letremove)
+
--------------------------------
-- Simple let binding removal
--------------------------------
-- Remove a = b bindings from let expressions everywhere
-letremovetop :: Transform
-letremovetop = everywhere ("letremove", inlinebind (\(b, e) -> Trans.lift $ is_local_var e))
+letremovesimpletop :: Transform
+letremovesimpletop = everywhere ("letremovesimple", inlinebind (\(b, e) -> Trans.lift $ is_local_var e))
--------------------------------
-- Unused let binding removal
--------------------------------
letremoveunused, letremoveunusedtop :: Transform
+letremoveunused expr@(Let (NonRec b bound) res) = do
+ let used = expr_uses_binders [b] res
+ if used
+ then return expr
+ else change res
letremoveunused expr@(Let (Rec binds) res) = do
-- Filter out all unused binds.
let binds' = filter dobind binds
letremoveunused expr = return expr
letremoveunusedtop = everywhere ("letremoveunused", letremoveunused)
+{-
--------------------------------
-- Identical let binding merging
--------------------------------
-- TODO: We would very much like to use GHC's CSE module for this, but that
-- doesn't track if something changed or not, so we can't use it properly.
letmerge, letmergetop :: Transform
-letmerge expr@(Let (Rec binds) res) = do
+letmerge expr@(Let _ _) = do
+ let (binds, res) = flattenLets expr
binds' <- domerge binds
- return (Let (Rec binds') res)
+ return $ mkNonRecLets binds' res
where
domerge :: [(CoreBndr, CoreExpr)] -> TransformMonad [(CoreBndr, CoreExpr)]
domerge [] = return []
-- Leave all other expressions unchanged
letmerge expr = return expr
letmergetop = everywhere ("letmerge", letmerge)
-
+-}
+
--------------------------------
-- Function inlining
--------------------------------
inlinenonreptop :: Transform
inlinenonreptop = everywhere ("inlinenonrep", inlinebind ((Monad.liftM not) . isRepr . snd))
+inlinetoplevel, inlinetopleveltop :: Transform
+-- Any system name is candidate for inlining. Never inline user-defined
+-- functions, to preserver structure.
+inlinetoplevel expr@(Var f) | not $ isUserDefined f = do
+ norm <- isNormalizeable f
+ -- See if this is a top level binding for which we have a body
+ body_maybe <- Trans.lift $ getGlobalBind f
+ if norm && Maybe.isJust body_maybe
+ then do
+ -- Get the normalized version
+ norm <- Trans.lift $ getNormalized f
+ if needsInline norm
+ then do
+ -- Regenerate all uniques in the to-be-inlined expression
+ norm_uniqued <- Trans.lift $ genUniques norm
+ change norm_uniqued
+ else
+ return expr
+ else
+ -- No body or not normalizeable.
+ return expr
+-- Leave all other expressions unchanged
+inlinetoplevel expr = return expr
+inlinetopleveltop = everywhere ("inlinetoplevel", inlinetoplevel)
+
+needsInline :: CoreExpr -> Bool
+needsInline expr = case splitNormalized expr of
+ -- Inline any function that only has a single definition, it is probably
+ -- simple enough. This might inline some stuff that it shouldn't though it
+ -- will never inline user-defined functions (inlinetoplevel only tries
+ -- system names) and inlining should never break things.
+ (args, [bind], res) -> True
+ _ -> False
+
--------------------------------
-- Scrutinee simplification
--------------------------------
if repr
then do
id <- Trans.lift $ mkBinderFor scrut "scrut"
- change $ Let (Rec [(id, scrut)]) (Case (Var id) b ty alts)
+ change $ Let (NonRec id scrut) (Case (Var id) b ty alts)
else
return expr
-- Leave all other expressions unchanged
(bindingss, alts') <- (Monad.liftM unzip) $ mapM doalt alts
let bindings = concat bindingss
-- Replace the case with a let with bindings and a case
- let newlet = (Let (Rec bindings) (Case scrut b ty alts'))
+ let newlet = mkNonRecLets bindings (Case scrut b ty alts')
-- If there are no non-wild binders, or this case is already a simple
-- selector (i.e., a single alt with exactly one binding), already a simple
-- selector altan no bindings (i.e., no wild binders in the original case),
(exprbinding_maybe, expr') <- doexpr expr uses_bndrs
-- Create a new alternative
let newalt = (con, newbndrs, expr')
- let bindings = Maybe.catMaybes (exprbinding_maybe : bindings_maybe)
+ let bindings = Maybe.catMaybes (bindings_maybe ++ [exprbinding_maybe])
return (bindings, newalt)
where
-- Make wild alternatives for each binder
-- binding containing a case expression.
dobndr :: CoreBndr -> Int -> TransformMonad (CoreBndr, Maybe (CoreBndr, CoreExpr))
dobndr b i = do
- repr <- isRepr (Var b)
+ repr <- isRepr b
-- Is b wild (e.g., not a free var of expr. Since b is only in scope
-- in expr, this means that b is unused if expr does not use it.)
let wild = not (VarSet.elemVarSet b free_vars)
if repr && not local_var
then do -- Extract representable arguments
id <- Trans.lift $ mkBinderFor arg "arg"
- change $ Let (Rec [(id, arg)]) (App f (Var id))
+ change $ Let (NonRec id arg) (App f (Var id))
else -- Leave non-representable arguments unchanged
return expr
-- Leave all other expressions unchanged
-- Perform this transform everywhere
funextracttop = everywhere ("funextract", funextract)
+--------------------------------
+-- Ensure that a function that just returns another function (or rather,
+-- another top-level binder) is still properly normalized. This is a temporary
+-- solution, we should probably integrate this pass with lambdasimpl and
+-- letsimpl instead.
+--------------------------------
+simplrestop expr@(Lam _ _) = return expr
+simplrestop expr@(Let _ _) = return expr
+simplrestop expr = do
+ local_var <- Trans.lift $ is_local_var expr
+ -- Don't extract values that are not representable, to prevent loops with
+ -- inlinenonrep
+ repr <- isRepr expr
+ if local_var || not repr
+ then
+ return expr
+ else do
+ id <- Trans.lift $ mkBinderFor expr "res"
+ change $ Let (NonRec id expr) (Var id)
--------------------------------
-- End of transformations
--------------------------------
-- What transforms to run?
-transforms = [argproptop, funextracttop, etatop, betatop, castproptop, letremovetop, letrectop, letsimpltop, letflattop, scrutsimpltop, casesimpltop, caseremovetop, inlinenonreptop, appsimpltop, letmergetop, letremoveunusedtop, castsimpltop]
+transforms = [inlinetopleveltop, argproptop, funextracttop, etatop, betatop, castproptop, letremovesimpletop, letderectop, letremovetop, letsimpltop, letflattop, scrutsimpltop, casesimpltop, caseremovetop, inlinenonreptop, appsimpltop, letremoveunusedtop, castsimpltop, lambdasimpltop, simplrestop]
-- | Returns the normalized version of the given function.
getNormalized ::
-> TranslatorSession CoreSyn.CoreExpr -- ^ The normalized expression
normalizeExpr what expr = do
- -- Introduce an empty Let at the top level, so there will always be
- -- a let in the expression (none of the transformations will remove
- -- the last let).
- let expr' = Let (Rec []) expr
+ expr_uniqued <- genUniques expr
-- Normalize this expression
- trace (what ++ " before normalization:\n\n" ++ showSDoc ( ppr expr' ) ++ "\n") $ return ()
- expr'' <- dotransforms transforms expr'
- trace ("\n" ++ what ++ " after normalization:\n\n" ++ showSDoc ( ppr expr'')) $ return ()
- return expr''
+ trace (what ++ " before normalization:\n\n" ++ showSDoc ( ppr expr_uniqued ) ++ "\n") $ return ()
+ expr' <- dotransforms transforms expr_uniqued
+ trace ("\n" ++ what ++ " after normalization:\n\n" ++ showSDoc ( ppr expr')) $ return ()
+ return expr'
-- | Get the value that is bound to the given binder at top level. Fails when
-- there is no such binding.
splitNormalized ::
CoreExpr -- ^ The normalized expression
-> ([CoreBndr], [Binding], CoreBndr)
-splitNormalized expr =
- case letexpr of
- (Let (Rec binds) (Var res)) -> (args, binds, res)
- _ -> error $ "Normalize.splitNormalized: Not in normal form: " ++ pprString expr ++ "\n"
+splitNormalized expr = (args, binds, res)
where
(args, letexpr) = CoreSyn.collectBinders expr
+ (binds, resexpr) = flattenLets letexpr
+ res = case resexpr of
+ (Var x) -> x
+ _ -> error $ "Normalize.splitNormalized: Not in normal form: " ++ pprString expr ++ "\n"
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