[llvm] [SelectionDAG] Add support to dump DAGs with sorted nodes (PR #161097)

[Craig Topper via llvm-commits]

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@@ -1061,13 +1061,23 @@ static void DumpNodes(const SDNode *N, unsigned indent, const SelectionDAG *G) {
   N->dump(G);
 }
 
-LLVM_DUMP_METHOD void SelectionDAG::dump() const {
+LLVM_DUMP_METHOD void SelectionDAG::dump(bool Sorted) const {
   dbgs() << "SelectionDAG has " << AllNodes.size() << " nodes:\n";
 
-  for (const SDNode &N : allnodes()) {
+  auto dumpEachNode = [this](const SDNode &N) {
     if (!N.hasOneUse() && &N != getRoot().getNode() &&
         (!shouldPrintInline(N, this) || N.use_empty()))
       DumpNodes(&N, 2, this);
+  };
+
+  if (Sorted) {
+    SmallVector<const SDNode *> SortedNodes(AllNodes.size());
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topperc wrote:

This is initializing AllNodes.size() elements in the vector so it will perform a memset. `getTopologicallyOrderedNodes` will clear the vector which will change the size, but not the capacity back to 0. Should we use `reserve` instead to avoid the memset?

https://github.com/llvm/llvm-project/pull/161097