-- 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
-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
- -- 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.
- return $ Let (Rec binds') expr
- where
- -- Turns a binding of a let into a multiple bindings, or any other binding
- -- 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, expr) = return [(b, expr)]
+letflat (Let (NonRec b (Let (NonRec b' expr') res')) res) =
+ change $ Let (NonRec b' expr') (Let (NonRec b res') res)
-- 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
-- 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 $ MkCore.mkCoreLets (map (uncurry NonRec) binds') res
where
domerge :: [(CoreBndr, CoreExpr)] -> TransformMonad [(CoreBndr, CoreExpr)]
domerge [] = return []
-- What transforms to run?
-transforms = [argproptop, funextracttop, etatop, betatop, castproptop, letremovetop, letderectop, letsimpltop, letflattop, scrutsimpltop, casesimpltop, caseremovetop, inlinenonreptop, appsimpltop, letmergetop, letremoveunusedtop, castsimpltop]
+transforms = [argproptop, funextracttop, etatop, betatop, castproptop, letremovesimpletop, letderectop, letremovetop, letsimpltop, letflattop, scrutsimpltop, casesimpltop, caseremovetop, inlinenonreptop, appsimpltop, letmergetop, letremoveunusedtop, castsimpltop]
-- | Returns the normalized version of the given function.
getNormalized ::
res = case resexpr of
(Var x) -> x
_ -> error $ "Normalize.splitNormalized: Not in normal form: " ++ pprString expr ++ "\n"
-
--- | Flattens nested lets into a single list of bindings. The expression
--- passed does not have to be a let expression, if it isn't an empty list of
--- bindings is returned.
-flattenLets ::
- CoreExpr -- ^ The expression to flatten.
- -> ([Binding], CoreExpr) -- ^ The bindings and resulting expression.
-flattenLets (Let binds expr) =
- (bindings ++ bindings', expr')
- where
- -- Recursively flatten the contained expression
- (bindings', expr') =flattenLets expr
- -- Flatten our own bindings to remove the Rec / NonRec constructors
- bindings = CoreSyn.flattenBinds [binds]
-flattenLets expr = ([], expr)
projects / matthijs / master-project / cλash.git / blobdiff