[llvm] [IA]: Construct (de)interleave4 out of (de)interleave2 (PR #89276)

[Paul Walker via llvm-commits]

================
@@ -531,14 +577,38 @@ bool InterleavedAccessImpl::lowerInterleaveIntrinsic(
     return false;
 
   LLVM_DEBUG(dbgs() << "IA: Found an interleave intrinsic: " << *II << "\n");
-
+  std::queue<IntrinsicInst *> IeinterleaveTreeQueue;
+  SmallVector<Value *> TempLeafNodes, LeafNodes;
+  SmallVector<Instruction *> TempDeadInsts;
+
+  IeinterleaveTreeQueue.push(II);
+  while (!IeinterleaveTreeQueue.empty()) {
+    auto node = IeinterleaveTreeQueue.front();
+    TempDeadInsts.push_back(node);
+    IeinterleaveTreeQueue.pop();
+    for (unsigned i = 0; i < 2; i++) {
+      auto op = node->getOperand(i);
+      if (auto CurrentII = dyn_cast<IntrinsicInst>(op)) {
+        if (CurrentII->getIntrinsicID() !=
+            Intrinsic::experimental_vector_interleave2)
+          continue;
+        IeinterleaveTreeQueue.push(CurrentII);
+        continue;
+      }
+      TempLeafNodes.push_back(op);
+    }
+  }
+  for (unsigned I = 0; I < TempLeafNodes.size(); I += 2)
+    LeafNodes.push_back(TempLeafNodes[I]);
+  for (unsigned I = 1; I < TempLeafNodes.size(); I += 2)
+    LeafNodes.push_back(TempLeafNodes[I]);
----------------
paulwalker-arm wrote:

This look rather more complex than I was expecting. I was hoping for something akin to:
```
match(II, interleave(interleave(Value(A), Value(C)), interleave(Value(B), Value(D)))
```
Have I got my logic wrong and thus the extra complexity is necessary?

https://github.com/llvm/llvm-project/pull/89276