[NFC] Mark LI.getLoopsInPreorder and LI.getLoopsInReverseSiblingPreorder const.

[fodinabor]

Summary

They create a new vector with the list, so they can be const.

[fhahn]

LGTM, thanks!

llvm/include/llvm/Analysis/LoopInfo.h

public:
   reverse_iterator rend() const { return TopLevelLoops.rend(); }
   bool empty() const { return TopLevelLoops.empty(); }
 
   /// Return all of the loops in the function in preorder across the loop
   /// nests, with siblings in forward program order.
   ///
   /// Note that because loops form a forest of trees, preorder is equivalent to
   /// reverse postorder.
-  SmallVector<LoopT *, 4> getLoopsInPreorder();
+  SmallVector<LoopT *, 4> getLoopsInPreorder() const;
 
   /// Return all of the loops in the function in preorder across the loop
   /// nests, with siblings in *reverse* program order.
   ///
   /// Note that because loops form a forest of trees, preorder is equivalent to
   /// reverse postorder.
   ///
   /// Also note that this is *not* a reverse preorder. Only the siblings are in
   /// reverse program order.
-  SmallVector<LoopT *, 4> getLoopsInReverseSiblingPreorder();
+  SmallVector<LoopT *, 4> getLoopsInReverseSiblingPreorder() const;
 
   /// Return the inner most loop that BB lives in. If a basic block is in no
   /// loop (for example the entry node), null is returned.
   LoopT *getLoopFor(const BlockT *BB) const { return BBMap.lookup(BB); }
 
   /// Same as getLoopFor.
   const LoopT *operator[](const BlockT *BB) const { return getLoopFor(BB); }
 

llvm/include/llvm/Analysis/LoopInfoImpl.h

void LoopInfoBase<BlockT, LoopT>::analyze(const DomTreeBase<BlockT> &DomTree) {
   }
   // Perform a single forward CFG traversal to populate block and subloop
   // vectors for all loops.
   PopulateLoopsDFS<BlockT, LoopT> DFS(this);
   DFS.traverse(DomRoot->getBlock());
 }
 
 template <class BlockT, class LoopT>
-SmallVector<LoopT *, 4> LoopInfoBase<BlockT, LoopT>::getLoopsInPreorder() {
+SmallVector<LoopT *, 4> LoopInfoBase<BlockT, LoopT>::getLoopsInPreorder() const {
   SmallVector<LoopT *, 4> PreOrderLoops, PreOrderWorklist;
   // The outer-most loop actually goes into the result in the same relative
   // order as we walk it. But LoopInfo stores the top level loops in reverse
   // program order so for here we reverse it to get forward program order.
   // FIXME: If we change the order of LoopInfo we will want to remove the
   // reverse here.
   for (LoopT *RootL : reverse(*this)) {
     auto PreOrderLoopsInRootL = RootL->getLoopsInPreorder();
     PreOrderLoops.append(PreOrderLoopsInRootL.begin(),
                          PreOrderLoopsInRootL.end());
   }
 
   return PreOrderLoops;
 }
 
 template <class BlockT, class LoopT>
 SmallVector<LoopT *, 4>
-LoopInfoBase<BlockT, LoopT>::getLoopsInReverseSiblingPreorder() {
+LoopInfoBase<BlockT, LoopT>::getLoopsInReverseSiblingPreorder() const {
   SmallVector<LoopT *, 4> PreOrderLoops, PreOrderWorklist;
   // The outer-most loop actually goes into the result in the same relative
   // order as we walk it. LoopInfo stores the top level loops in reverse
   // program order so we walk in order here.
   // FIXME: If we change the order of LoopInfo we will want to add a reverse
   // here.
   for (LoopT *RootL : *this) {
     assert(PreOrderWorklist.empty() &&