Make .bc en/decoding of AttrKind stable

The bitcode representation attribute kinds are encoded into / decoded from
should be independent of the current set of LLVM attributes and their position
in the AttrKind enum. This patch explicitly encodes attributes to fixed bitcode
values.

With this patch applied, LLVM does not silently misread attributes written by
LLVM 3.3. We also enhance the decoding slightly such that an error message is
printed if an unknown AttrKind encoding was dected.

Bonus: Dropping bitcode attributes from AttrKind is now easy, as old AttrKinds
       do not need to be kept to support the Bitcode reader.
llvm-svn: 187186

1 files changed, 1 insertions, 0 deletions

diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.h b/llvm/lib/Bitcode/Reader/BitcodeReader.h
index e4de4ab7c7c..b095447675a 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.h
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.h
@@ -321,6 +321,7 @@ private:
     return getFnValueByID(ValNo, Ty);
   }
 
+  bool ParseAttrKind(uint64_t Code, Attribute::AttrKind *Kind);
   bool ParseModule(bool Resume);
   bool ParseAttributeBlock();
   bool ParseAttributeGroupBlock();