[llvm] Fix crash when complex deinterleaving operates on an unrolled loop (#129735)

When attempting to perform complex deinterleaving on an unrolled loop
containing a reduction, the complex deinterleaving pass would fail to
accommodate the wider types when accumulating the unrolled paths.
Instead of trying to alter the incoming IR to fit expectations, the pass
should instead decide against processing any reduction that results in a
non-complex or non-vector value.

Author: NickGuy-Arm

llvm/lib/CodeGen/ComplexDeinterleavingPass.cpp

@@ -1741,6 +1741,17 @@ void ComplexDeinterleavingGraph::identifyReductionNodes() {
       LLVM_DEBUG(
           dbgs() << "Identified single reduction starting from instruction: "
                  << *Real << "/" << *ReductionInfo[Real].second << "\n");
+
+      // Reducing to a single vector is not supported, only permit reducing down
+      // to scalar values.
+      // Doing this here will leave the prior node in the graph,
+      // however with no uses the node will be unreachable by the replacement
+      // process. That along with the usage outside the graph should prevent the
+      // replacement process from kicking off at all for this graph.
+      // TODO Add support for reducing to a single vector value
+      if (ReductionInfo[Real].second->getType()->isVectorTy())
+        continue;
+
       Processed[i] = true;
       auto RootNode = prepareCompositeNode(
           ComplexDeinterleavingOperation::ReductionSingle, Real, nullptr);