Another useful monomorphisation rewrite

2 files changed, 17 insertions, 0 deletions

diff --git a/lib/mono_rewrites.sail b/lib/mono_rewrites.sail
index a72cdd79..144b7ae0 100644
--- a/lib/mono_rewrites.sail
+++ b/lib/mono_rewrites.sail
@@ -110,3 +110,11 @@ function sext_slice(xs,i,l) = {
   let xs = (xs & slice_mask(i,l)) >> i in
   extsv(xs)
 }
+
+val UInt_slice : forall 'n, 'n >= 0.
+  (bits('n), int, int) -> int effect pure
+
+function UInt_slice(xs,i,l) = {
+  let xs = (xs & slice_mask(i,l)) >> i in
+  UInt(xs)
+}
diff --git a/src/monomorphise.ml b/src/monomorphise.ml
index b77b49cf..9f67e93f 100644
--- a/src/monomorphise.ml
+++ b/src/monomorphise.ml
@@ -2778,6 +2778,15 @@ let rewrite_app env typ (id,args) =
 
     | _ -> E_app (id,args)
 
+  else if is_id env (Id "UInt") id then
+    let is_slice = is_id env (Id "slice") in
+    match args with
+    | [E_aux (E_app (slice1, [vector1; start1; length1]),_)]
+        when is_slice slice1 && not (is_constant length1) ->
+       E_app (mk_id "UInt_slice", [vector1; start1; length1])
+
+    | _ -> E_app (id,args)
+
   else E_app (id,args)
 
 let rewrite_aux = function