5 files changed, 43 insertions, 9 deletions

diff --git a/llvm/include/llvm/ADT/ilist.h b/llvm/include/llvm/ADT/ilist.h
index 62e434010dd..06c7abff965 100644
--- a/llvm/include/llvm/ADT/ilist.h
+++ b/llvm/include/llvm/ADT/ilist.h
@@ -65,9 +65,8 @@ template <typename NodeTy> struct ilist_callback_traits {
   void addNodeToList(NodeTy *) {}
   void removeNodeFromList(NodeTy *) {}
 
-  /// Callback before transferring nodes to this list.
-  ///
-  /// \pre \c this!=&OldList
+  /// Callback before transferring nodes to this list. The nodes may already be
+  /// in this same list.
   template <class Iterator>
   void transferNodesFromList(ilist_callback_traits &OldList, Iterator /*first*/,
                              Iterator /*last*/) {
@@ -286,8 +285,8 @@ private:
     if (position == last)
       return;
 
-    if (this != &L2) // Notify traits we moved the nodes...
-      this->transferNodesFromList(L2, first, last);
+    // Notify traits we moved the nodes...
+    this->transferNodesFromList(L2, first, last);
 
     base_list_type::splice(position, L2, first, last);
   }
diff --git a/llvm/include/llvm/CodeGen/MachineFunction.h b/llvm/include/llvm/CodeGen/MachineFunction.h
index a3b13fb2438..670b2d501af 100644
--- a/llvm/include/llvm/CodeGen/MachineFunction.h
+++ b/llvm/include/llvm/CodeGen/MachineFunction.h
@@ -85,7 +85,7 @@ template <> struct ilist_callback_traits<MachineBasicBlock> {
 
   template <class Iterator>
   void transferNodesFromList(ilist_callback_traits &OldList, Iterator, Iterator) {
-    llvm_unreachable("Never transfer between lists");
+    assert(this == &OldList && "never transfer MBBs between functions");
   }
 };
 
diff --git a/llvm/lib/CodeGen/MachineBasicBlock.cpp b/llvm/lib/CodeGen/MachineBasicBlock.cpp
index df4762088c1..c3e9c185be9 100644
--- a/llvm/lib/CodeGen/MachineBasicBlock.cpp
+++ b/llvm/lib/CodeGen/MachineBasicBlock.cpp
@@ -132,8 +132,12 @@ void ilist_traits<MachineInstr>::transferNodesFromList(ilist_traits &FromList,
                                                        instr_iterator First,
                                                        instr_iterator Last) {
   assert(Parent->getParent() == FromList.Parent->getParent() &&
-        "MachineInstr parent mismatch!");
-  assert(this != &FromList && "Called without a real transfer...");
+         "cannot transfer MachineInstrs between MachineFunctions");
+
+  // If it's within the same BB, there's nothing to do.
+  if (this == &FromList)
+    return;
+
   assert(Parent != FromList.Parent && "Two lists have the same parent?");
 
   // If splicing between two blocks within the same function, just update the
diff --git a/llvm/lib/IR/SymbolTableListTraitsImpl.h b/llvm/lib/IR/SymbolTableListTraitsImpl.h
index a74ac8a960f..f399c823d6f 100644
--- a/llvm/lib/IR/SymbolTableListTraitsImpl.h
+++ b/llvm/lib/IR/SymbolTableListTraitsImpl.h
@@ -83,7 +83,8 @@ void SymbolTableListTraits<ValueSubClass>::transferNodesFromList(
     SymbolTableListTraits &L2, iterator first, iterator last) {
   // We only have to do work here if transferring instructions between BBs
   ItemParentClass *NewIP = getListOwner(), *OldIP = L2.getListOwner();
-  assert(NewIP != OldIP && "Expected different list owners");
+  if (NewIP == OldIP)
+    return;
 
   // We only have to update symbol table entries if we are transferring the
   // instructions to a different symtab object...
diff --git a/llvm/unittests/ADT/IListTest.cpp b/llvm/unittests/ADT/IListTest.cpp
index 3992a235403..18f6c41a648 100644
--- a/llvm/unittests/ADT/IListTest.cpp
+++ b/llvm/unittests/ADT/IListTest.cpp
@@ -207,6 +207,12 @@ struct NodeWithCallback : ilist_node<NodeWithCallback> {
 } // end namespace
 
 namespace llvm {
+// These nodes are stack-allocated for testing purposes, so don't let the ilist
+// own or delete them.
+template <> struct ilist_alloc_traits<NodeWithCallback> {
+  static void deleteNode(NodeWithCallback *) {}
+};
+
 template <> struct ilist_callback_traits<NodeWithCallback> {
   void addNodeToList(NodeWithCallback *N) { N->IsInList = true; }
   void removeNodeFromList(NodeWithCallback *N) { N->IsInList = false; }
@@ -247,6 +253,30 @@ TEST(IListTest, addNodeToList) {
   ASSERT_TRUE(N.WasTransferred);
 }
 
+TEST(IListTest, sameListSplice) {
+  NodeWithCallback N1(1);
+  NodeWithCallback N2(2);
+  ASSERT_FALSE(N1.WasTransferred);
+  ASSERT_FALSE(N2.WasTransferred);
+
+  ilist<NodeWithCallback> L1;
+  L1.insert(L1.end(), &N1);
+  L1.insert(L1.end(), &N2);
+  ASSERT_EQ(2u, L1.size());
+  ASSERT_EQ(&N1, &L1.front());
+  ASSERT_FALSE(N1.WasTransferred);
+  ASSERT_FALSE(N2.WasTransferred);
+
+  // Swap the nodes with splice inside the same list. Check that we get the
+  // transfer callback.
+  L1.splice(L1.begin(), L1, std::next(L1.begin()), L1.end());
+  ASSERT_EQ(2u, L1.size());
+  ASSERT_EQ(&N1, &L1.back());
+  ASSERT_EQ(&N2, &L1.front());
+  ASSERT_FALSE(N1.WasTransferred);
+  ASSERT_TRUE(N2.WasTransferred);
+}
+
 struct PrivateNode : private ilist_node<PrivateNode> {
   friend struct llvm::ilist_detail::NodeAccess;