add a nate note

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@30399 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/README.txt b/lib/Target/README.txt
index 86c231bf319609e3b9e7f20bc61cd556a15f4583..1f982b7f76a6a527b4660140331bdf9230acf8f8 100644 (file)
--- a/lib/Target/README.txt
+++ b/lib/Target/README.txt
@@ -240,4 +240,10 @@ _bar:   addic r3,r3,-1
         subfe r3,r3,r3
         blr
 
+//===---------------------------------------------------------------------===//
+
+Legalize should lower ctlz like this:
+  ctlz(x) = popcnt((x-1) & ~x)
+
+on targets that have popcnt but not ctlz.  itanium, what else?