Implement blocklength reduction

compiler/src/l3/CPSOptimizer.scala

@@ -142,14 +142,21 @@ abstract class CPSOptimizer[T <: CPSTreeModule { type Name = Symbol }]
           // Right Absorbing
           case Seq(a1, AtomL(l2)) if rightAbsorbing((prim, l2)) =>
             shrink(body, s.withASubst(name, l2))
-          case Seq(a1) if prim == blockTag && s.eEnv.isDefinedAt(a1) =>
-            val maybeBlockAlloc = s.eEnv(a1)._1
+          case Seq(a1) if s.eEnv.isDefinedAt(a1) =>
+            val (maybeBlockAlloc, maybeLengthAtom) = s.eEnv(a1)
             blockAllocTag.lift(maybeBlockAlloc) match {
               case Some(tag) =>
+                if (prim == blockTag) {
                   shrink(body, s.withASubst(name, AtomL(tag)))
+                } else if (prim == blockLength) {
+                  shrink(body, s.withASubst(name, maybeLengthAtom(0)))
+                } else {
+                  noOp
+                }
               case None =>
                 noOp
             }
+
           case _ => noOp
         }
       }