From 481f492ecc3179f5ea8293dab45c3712871c219e Mon Sep 17 00:00:00 2001
From: Brian Campbell
Date: Fri, 26 Jan 2018 17:52:16 +0000
Subject: One more mono rewrite

---
 lib/mono_rewrites.sail | 7 +++++++
 src/monomorphise.ml    | 4 ++++
 2 files changed, 11 insertions(+)

diff --git a/lib/mono_rewrites.sail b/lib/mono_rewrites.sail
index fd1d1b23..a69dc379 100644
--- a/lib/mono_rewrites.sail
+++ b/lib/mono_rewrites.sail
@@ -122,3 +122,10 @@ function UInt_slice(xs,i,l) = {
   let xs = (xs & slice_mask(i,l)) >> i in
   UInt(xs)
 }
+
+val zext_ones : forall 'n, 'n >= 0. int -> bits('n) effect pure
+
+function zext_ones(m) = {
+  let v : bits('n) = extsv(0b1) in
+  v >> ('n - m)
+}
diff --git a/src/monomorphise.ml b/src/monomorphise.ml
index cd2c419f..745b40e4 100644
--- a/src/monomorphise.ml
+++ b/src/monomorphise.ml
@@ -3075,6 +3075,10 @@ let rewrite_app env typ (id,args) =
         when is_slice slice1 && not (is_constant length1) ->
        E_app (mk_id "zext_slice", [vector1; start1; length1])
 
+    | [E_aux (E_app (ones, [len1]),_);
+       _ (* unnecessary ZeroExtend length *)] ->
+       E_app (mk_id "zext_ones", [len1])
+
     | _ -> E_app (id,args)
 
   else if is_id env (Id "SignExtend") id then
-- 
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