Add lambdasimpl normalization pass.

This pass puts the value of a lambda in a let binding, to make a lambda
always evaluate to either a let or a simple variable reference. This was
previously not needed, since there used to be a let always (even an empty
one), but this is no longer the case.

diff --git a/cλash/CLasH/Normalize.hs b/cλash/CLasH/Normalize.hs
index 984d739f830e0f11c2e45fb60d822a6d21a6a12c..85760bebd7e63026fc8f7ff815615c0123252a91 100644 (file)
--- a/cλash/CLasH/Normalize.hs
+++ b/cλash/CLasH/Normalize.hs
@@ -115,6 +115,36 @@ castsimpl expr = return expr
 -- 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 derecursification
 --------------------------------
@@ -566,7 +596,7 @@ funextracttop = everywhere ("funextract", funextract)
 
 
 -- What transforms to run?
-transforms = [argproptop, funextracttop, etatop, betatop, castproptop, letremovesimpletop, letderectop, letremovetop, 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, lambdasimpltop]
 
 -- | Returns the normalized version of the given function.
 getNormalized ::