add a nate note

llvm-svn: 30399
2006-09-15 20:31:36 +00:00 · 2006-09-15 20:31:36 +00:00 · c9dc375d3e
parent 1bcb3d16cc
commit c9dc375d3e
1 changed files with 6 additions and 0 deletions
--- a/llvm/lib/Target/README.txt
+++ b/llvm/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?