[llvm] [CodeLayout] Faster basic block reordering, ext-tsp (PR #68617)

[David Li via llvm-commits]

================
@@ -475,14 +478,14 @@ void ChainT::mergeEdges(ChainT *Other) {
   }
 }
 
-using NodeIter = std::vector<NodeT *>::const_iterator;
+/// A wrapper around three concatenated vectors (chains) of objects; it is used
+/// to avoid extra instantiation of the vectors.
+template <typename ObjType> struct MergedVector {
+  using ObjIter = typename std::vector<ObjType *>::const_iterator;
 
-/// A wrapper around three chains of nodes; it is used to avoid extra
-/// instantiation of the vectors.
-struct MergedChain {
-  MergedChain(NodeIter Begin1, NodeIter End1, NodeIter Begin2 = NodeIter(),
-              NodeIter End2 = NodeIter(), NodeIter Begin3 = NodeIter(),
-              NodeIter End3 = NodeIter())
+  MergedVector(ObjIter Begin1, ObjIter End1, ObjIter Begin2 = ObjIter(),
----------------
david-xl wrote:

perhaps a separate PR?

https://github.com/llvm/llvm-project/pull/68617