diff --git a/include/llvm/Bytecode/Format.h b/include/llvm/Bytecode/Format.h
index 466865e32db..ebcb3b84416 100644
--- a/include/llvm/Bytecode/Format.h
+++ b/include/llvm/Bytecode/Format.h
@@ -36,11 +36,17 @@ public:
     // Function subtypes:
     // Can also have ConstantPool block
     // Can also have SymbolTable block
-    BasicBlock = 0x31,        // May contain many basic blocks
+    BasicBlock = 0x31,// May contain many basic blocks (obsolete since LLVM 1.1)
 
     // InstructionList - The instructions in the body of a function.  This
-    // superceeds the old BasicBlock node.
+    // superceeds the old BasicBlock node used in LLVM 1.0.
     InstructionList = 0x32,
+
+    // CompactionTable - blocks with this id are used to define local remapping
+    // tables for a function, allowing the indices used within the function to
+    // be as small as possible.  This often allows the instructions to be
+    // encoded more efficiently.
+    CompactionTable = 0x33,
   };
 };