[llvm] [Support] Store dominator tree nodes in a vector (PR #101705)

[Nikita Popov via llvm-commits]

================
@@ -786,17 +837,54 @@ class DominatorTreeBase {
     DFSInfoValid = true;
   }
 
+private:
+  template <class T_ = NodeT>
+  std::enable_if_t<is_detected<has_number_t, T_>::value, void>
+  updateBlockNumberEpoch() {
+    BlockNumberEpoch = GraphTraits<ParentPtr>::getNumberEpoch(Parent);
+  }
+
+  template <class T_ = NodeT>
+  std::enable_if_t<!is_detected<has_number_t, T_>::value, void>
+  updateBlockNumberEpoch() {
+    // Nothing to do for graphs that don't number their blocks.
+  }
+
+public:
   /// recalculate - compute a dominator tree for the given function
   void recalculate(ParentType &Func) {
     Parent = &Func;
+    updateBlockNumberEpoch();
     DomTreeBuilder::Calculate(*this);
   }
 
   void recalculate(ParentType &Func, ArrayRef<UpdateType> Updates) {
     Parent = &Func;
+    updateBlockNumberEpoch();
     DomTreeBuilder::CalculateWithUpdates(*this, Updates);
   }
 
+  /// Update dominator tree after renumbering blocks
+  template <class T_ = NodeT>
+  std::enable_if_t<is_detected<has_number_t, T_>::value, void>
+  updateBlockNumbers() {
+    updateBlockNumberEpoch();
+
+    unsigned MaxNumber = GraphTraits<ParentPtr>::getMaxNumber(Parent);
+    DomTreeNodeStorageTy NewVector;
+    NewVector.resize(MaxNumber + 1); // +1, because index 0 is for nullptr
+    for (auto &Node : DomTreeNodes) {
+      if (!Node)
+        continue;
+      unsigned Idx = *getNodeIndex(Node->getBlock());
+      // getMaxNumber is not necssarily supported
----------------
nikic wrote:

```suggestion
      // getMaxNumber is not necessarily supported
```

https://github.com/llvm/llvm-project/pull/101705