Index: include/llvm/Bitcode/LLVMBitCodes.h
===================================================================
--- include/llvm/Bitcode/LLVMBitCodes.h
+++ include/llvm/Bitcode/LLVMBitCodes.h
@@ -34,7 +34,8 @@
     CONSTANTS_BLOCK_ID,
     FUNCTION_BLOCK_ID,
 
-    UNUSED_ID1,
+    // Valid inside vendor specific toolchains only, discarded by open-source
+    VENDOR_RESERVED_ID,
 
     VALUE_SYMTAB_BLOCK_ID,
     METADATA_BLOCK_ID,
Index: test/Bitcode/vendor_block.test
===================================================================
--- /dev/null
+++ test/Bitcode/vendor_block.test
@@ -0,0 +1,6 @@
+# Check that a global vendor block is correctly ignored 
+# and skipped by the vanilla bitcode reader
+
+; RUN: opt -S %p/Inputs/vendor_block.bc | FileCheck %s
+; CHECK: target triple = "x86_64-apple-macosx10.9"
+