diff --git a/llvm/include/llvm/CodeGen/TargetRegisterInfo.h b/llvm/include/llvm/CodeGen/TargetRegisterInfo.h
--- a/llvm/include/llvm/CodeGen/TargetRegisterInfo.h
+++ b/llvm/include/llvm/CodeGen/TargetRegisterInfo.h
@@ -875,7 +875,8 @@
 
   /// Allow the target to override the cost of using a callee-saved register for
   /// the first time. Default value of 0 means we will use a callee-saved
-  /// register if it is available.
+  /// register if it is available. This value is set assuming entry block
+  /// frequency is 1<<14.
   virtual unsigned getCSRFirstUseCost() const { return 0; }
 
   /// Returns true if the target requires (and can make use of) the register