[CASDB] OnDiskCAS should not create LeafNode when node has refs

Fix a bug that OnDiskCAS drops all the references when the data is
large and a leaf node is created. Leaf node should only be used when
there are no refs.

Author: cachemeifyoucan

llvm/lib/CAS/OnDiskCAS.cpp

@@ -1903,7 +1903,7 @@ Expected<NodeHandle> OnDiskCAS::storeNodeImpl(ArrayRef<uint8_t> ComputedHash,
   }
 
   // Big leaf nodes.
-  if (Data.size() > TrieRecord::MaxEmbeddedSize)
+  if (Refs.empty() && Data.size() > TrieRecord::MaxEmbeddedSize)
     return createStandaloneLeaf(I, Data);
 
   // TODO: Check whether it's worth checking the index for an already existing

llvm/unittests/CAS/CASDBTest.cpp

@@ -400,15 +400,21 @@ TEST_P(CASDBTest, NodesBig) {
   if (Storage.size() < SizeE)
     Storage.resize(SizeE, '\01');
 
+  SmallVector<CASID, 4> CreatedNodes;
   // Avoid checking every size because this is an expensive test. Just check
-  // for data that is 8B-word-aligned, and one less.
+  // for data that is 8B-word-aligned, and one less. Also appending the created
+  // nodes as the references in the next block to check references are created
+  // correctly.
   for (size_t Size = SizeB; Size < SizeE; Size += WordSize) {
     for (bool IsAligned : {false, true}) {
       StringRef Data(Storage.data(), Size - (IsAligned ? 0 : 1));
       Optional<NodeProxy> Node;
-      ASSERT_THAT_ERROR(CAS->createNode(None, Data).moveInto(Node), Succeeded());
+      ASSERT_THAT_ERROR(CAS->createNode(CreatedNodes, Data).moveInto(Node),
+                        Succeeded());
       ASSERT_EQ(Data, Node->getData());
       ASSERT_EQ(0, Node->getData().end()[0]);
+      ASSERT_EQ(Node->getNumReferences(), CreatedNodes.size());
+      CreatedNodes.emplace_back(Node->getID());
     }
   }
 }