diff --git a/lib/Target/X86/README.txt b/lib/Target/X86/README.txt
index 3e2eaef3e50..651d4729022 100644
--- a/lib/Target/X86/README.txt
+++ b/lib/Target/X86/README.txt
@@ -566,3 +566,21 @@ LBB_foo_3:      # no_exit
         jb LBB_foo_3    # no_exit
 
 //===---------------------------------------------------------------------===//
+
+Codegen:
+  if (copysign(1.0, x) == copysign(1.0, y))
+into:
+  if (x^y & mask)
+when using SSE.
+
+//===---------------------------------------------------------------------===//
+
+Optimize this into something reasonable:
+ x * copysign(1.0, y) * copysign(1.0, z)
+
+//===---------------------------------------------------------------------===//
+
+Optimize copysign(x, *y) to use an integer load from y.
+
+//===---------------------------------------------------------------------===//
+