diff --git a/wip-duuqnd/user-side-compiler/middle/data.lisp b/wip-duuqnd/user-side-compiler/middle/data.lisp
index 6ba6496..a9e6841 100644
--- a/wip-duuqnd/user-side-compiler/middle/data.lisp
+++ b/wip-duuqnd/user-side-compiler/middle/data.lisp
@@ -1,7 +1,8 @@
 (in-package #:user-side-compiler)
 
 (defclass ir-data ()
-  ((%definition :accessor definition :initarg :definition)))
+  ((%definition :accessor definition :initarg :definition)
+   (%last-use :accessor last-use)))
 
 (defclass ir-result (ir-data)
   ((%user :accessor user :initarg :user :initform nil)))
diff --git a/wip-duuqnd/user-side-compiler/middle/optimizations.lisp b/wip-duuqnd/user-side-compiler/middle/optimizations.lisp
index 2755b81..f33ca09 100644
--- a/wip-duuqnd/user-side-compiler/middle/optimizations.lisp
+++ b/wip-duuqnd/user-side-compiler/middle/optimizations.lisp
@@ -168,3 +168,10 @@ though I'm pretty sure it can't anyway.")
                   (push input arguments))))
           (loop :for (new . old) :in replacements
                 :do (setf (inputs call) (substitute new old (inputs call)))))))))
+
+(defun compute-lifetime-knowledge (start-iblock)
+  (do-iblocks (iblock start-iblock)
+    (do-instructions (inst iblock)
+      (loop :for data :in (inputs inst)
+            :when (typep data 'ir-data)
+              :do (setf (last-use data) inst)))))