Add an addition operator to TableGen

This adds an !add(a, b) operator to tablegen; this will be used
to cleanup the PPC register definitions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173445 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/TableGen/LangRef.rst b/docs/TableGen/LangRef.rst
index 92fdb4a..53fbe2d 100644
--- a/docs/TableGen/LangRef.rst
+++ b/docs/TableGen/LangRef.rst
@@ -91,7 +91,7 @@
 .. productionlist::
    BangOperator: one of
                :!eq     !if      !head    !tail      !con
-               :!shl    !sra     !srl
+               :!add    !shl     !sra     !srl
                :!cast   !empty   !subst   !foreach   !strconcat
 
 Syntax