Turn let recursification into its opposite.

Instead of making all lets recursive, it now makes all lets nonrecursive,
wherever possible. This breaks normalization, since most other passes work
with recursive lets exclusively.

diff --git a/cλash/CLasH/Normalize.hs b/cλash/CLasH/Normalize.hs
index 1d40f92d52f7b94989fc9215bcfd15723a9001e0..9828d5ceea96704f92b979766dd06be5bfcc7523 100644 (file)
--- a/cλash/CLasH/Normalize.hs
+++ b/cλash/CLasH/Normalize.hs
@@ -9,6 +9,7 @@ module CLasH.Normalize (getNormalized, normalizeExpr, splitNormalized) where
 -- 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
@@ -115,14 +116,31 @@ castsimpl expr = return expr
 castsimpltop = everywhere ("castsimpl", castsimpl)
 
 --------------------------------
--- 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 $ MkCore.mkCoreLets newbinds 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
+    -- Create nonrec bindings for each liftable binding and a single recursive
+    -- binding for all others
+    newbinds = (map (uncurry NonRec) liftable) ++ [Rec nonliftable]
+    -- 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
@@ -545,7 +563,7 @@ funextracttop = everywhere ("funextract", funextract)
 
 
 -- What transforms to run?
-transforms = [argproptop, funextracttop, etatop, betatop, castproptop, letremovetop, letrectop, letsimpltop, letflattop, scrutsimpltop, casesimpltop, caseremovetop, inlinenonreptop, appsimpltop, letmergetop, letremoveunusedtop, castsimpltop]
+transforms = [argproptop, funextracttop, etatop, betatop, castproptop, letremovetop, letderectop, letsimpltop, letflattop, scrutsimpltop, casesimpltop, caseremovetop, inlinenonreptop, appsimpltop, letmergetop, letremoveunusedtop, castsimpltop]
 
 -- | Returns the normalized version of the given function.
 getNormalized ::