[VPlan] Add findComputeReductionResult helper. (NFC)

Move utility to helper for re-use in follow-up patches.

Author: fhahn

llvm/lib/Transforms/Vectorize/VPlanConstruction.cpp

@@ -796,6 +796,17 @@ void VPlanTransforms::addMinimumVectorEpilogueIterationCheck(
   Branch->addMetadata(LLVMContext::MD_prof, BranchWeights);
 }
 
+/// If \p RedPhiR is used by a ComputeReductionResult recipe, return it.
+/// Otherwise return nullptr.
+static VPInstruction *
+findComputeReductionResult(VPReductionPHIRecipe *RedPhiR) {
+  auto It = find_if(RedPhiR->users(), [](VPUser *U) {
+    auto *VPI = dyn_cast<VPInstruction>(U);
+    return VPI && VPI->getOpcode() == VPInstruction::ComputeReductionResult;
+  });
+  return It == RedPhiR->user_end() ? nullptr : cast<VPInstruction>(*It);
+}
+
 bool VPlanTransforms::handleMaxMinNumReductions(VPlan &Plan) {
   auto GetMinMaxCompareValue = [](VPReductionPHIRecipe *RedPhiR) -> VPValue * {
     auto *MinMaxR =
@@ -900,13 +911,7 @@ bool VPlanTransforms::handleMaxMinNumReductions(VPlan &Plan) {
 
     // If we exit early due to NaNs, compute the final reduction result based on
     // the reduction phi at the beginning of the last vector iteration.
-    auto *RdxResult = find_singleton<VPSingleDefRecipe>(
-        RedPhiR->users(), [](VPUser *U, bool) -> VPSingleDefRecipe * {
-          auto *VPI = dyn_cast<VPInstruction>(U);
-          if (VPI && VPI->getOpcode() == VPInstruction::ComputeReductionResult)
-            return VPI;
-          return nullptr;
-        });
+    auto *RdxResult = findComputeReductionResult(RedPhiR);
 
     auto *NewSel = MiddleBuilder.createSelect(AnyNaNLane, RedPhiR,
                                               RdxResult->getOperand(1));