Added special treatment of serializing NULL pointers.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@43357 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Bitcode/Writer/Serialize.cpp b/lib/Bitcode/Writer/Serialize.cpp
index fbe1d10..a1d7320 100644
--- a/lib/Bitcode/Writer/Serialize.cpp
+++ b/lib/Bitcode/Writer/Serialize.cpp
@@ -58,10 +58,13 @@
 }
 
 unsigned Serializer::getPtrId(void* ptr) {
+  if (!ptr)
+    return 0;
+  
   MapTy::iterator I = PtrMap.find(ptr);
   
   if (I == PtrMap.end()) {
-    unsigned id = PtrMap.size();
+    unsigned id = PtrMap.size()+1;
     PtrMap[ptr] = id;
     return id;
   }