[llvm] r266256 - [IR] Optimize memory usage of Metadata on MSVC

[Reid Kleckner via llvm-commits]

Author: rnk
Date: Wed Apr 13 17:46:06 2016
New Revision: 266256

URL: http://llvm.org/viewvc/llvm-project?rev=266256&view=rev
Log:
[IR] Optimize memory usage of Metadata on MSVC

An unsigned 2 bit bitfield takes 4 bytes in MSVC. Instead of a bitfield,
just use an unsigned char. We can go back to a bitfield when someone
implements the TODO of exposing and reusing the remaining 6 bits.

Modified:
    llvm/trunk/include/llvm/IR/Metadata.h

Modified: llvm/trunk/include/llvm/IR/Metadata.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/IR/Metadata.h?rev=266256&r1=266255&r2=266256&view=diff
==============================================================================
--- llvm/trunk/include/llvm/IR/Metadata.h (original)
+++ llvm/trunk/include/llvm/IR/Metadata.h Wed Apr 13 17:46:06 2016
@@ -52,7 +52,7 @@ protected:
   enum StorageType { Uniqued, Distinct, Temporary };
 
   /// \brief Storage flag for non-uniqued, otherwise unowned, metadata.
-  unsigned Storage : 2;
+  unsigned char Storage;
   // TODO: expose remaining bits to subclasses.
 
   unsigned short SubclassData16;
@@ -93,6 +93,7 @@ public:
 protected:
   Metadata(unsigned ID, StorageType Storage)
       : SubclassID(ID), Storage(Storage), SubclassData16(0), SubclassData32(0) {
+    static_assert(sizeof(*this) == 8, "Metdata fields poorly packed");
   }
   ~Metadata() = default;