[llvm] Add NCD search on Array of basic blocks

Author: enoskova-sc

llvm/include/llvm/CodeGen/MachineDominators.h

@@ -185,6 +185,11 @@ class MachineDominatorTree : public DomTreeBase<MachineBasicBlock> {
     return Base::findNearestCommonDominator(A, B);
   }
 
+  /// Returns the nearest common dominator of the given blocks.
+  /// If that tree node is a virtual root, a nullptr will be returned.
+  MachineBasicBlock *
+  findNearestCommonDominator(ArrayRef<MachineBasicBlock *> Blocks) const;
+
   MachineDomTreeNode *operator[](MachineBasicBlock *BB) const {
     applySplitCriticalEdges();
     return Base::getNode(BB);

llvm/lib/CodeGen/MachineDominators.cpp

@@ -189,3 +189,19 @@ void MachineDominatorTree::applySplitCriticalEdges() const {
   NewBBs.clear();
   CriticalEdgesToSplit.clear();
 }
+
+MachineBasicBlock *MachineDominatorTree::findNearestCommonDominator(
+    ArrayRef<MachineBasicBlock *> Blocks) const {
+  assert(!Blocks.empty());
+
+  MachineBasicBlock *NCD = Blocks.front();
+  for (MachineBasicBlock *BB : Blocks.drop_front()) {
+    NCD = Base::findNearestCommonDominator(NCD, BB);
+
+    // Stop when the root is reached.
+    if (Base::isVirtualRoot(Base::getNode(NCD)))
+      return nullptr;
+  }
+
+  return NCD;
+}