diff --git a/llvm/include/llvm/CodeGen/ISDOpcodes.h b/llvm/include/llvm/CodeGen/ISDOpcodes.h
--- a/llvm/include/llvm/CodeGen/ISDOpcodes.h
+++ b/llvm/include/llvm/CodeGen/ISDOpcodes.h
@@ -284,9 +284,12 @@
   /// rhs to the add or sub, and the third is a boolean indicating if there
   /// is an incoming carry. These nodes produce two results: the normal
   /// result of the add or sub, and the output carry so they can be chained
-  /// together. The use of this opcode is preferable to adde/sube if the
-  /// target supports it, as the carry is a regular value rather than a
-  /// glue, which allows further optimisation.
+  /// together. Both the incoming and outgoing carries are active high with 1
+  /// indicating the presence of a carry/borrow. Care should be taken on those
+  /// hardware architectures where some instructions use the active-low logic
+  /// for the carry/borrow flag. The use of this opcode is preferable to
+  /// adde/sube if the target supports it, as the carry is a regular value
+  /// rather than a glue, which allows further optimisation.
   ADDCARRY,
   SUBCARRY,