[SLP][NFC]Add some extra checks/reorganize the code to improve compile time, NFC.

Author: alexey-bataev

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -4104,6 +4104,8 @@ BoUpSLP::getReorderingData(const TreeEntry &TE, bool TopToBottom) {
   // No need to reorder if need to shuffle reuses, still need to shuffle the
   // node.
   if (!TE.ReuseShuffleIndices.empty()) {
+    if (isSplat(TE.Scalars))
+      return std::nullopt;
     // Check if reuse shuffle indices can be improved by reordering.
     // For this, check that reuse mask is "clustered", i.e. each scalar values
     // is used once in each submask of size <number_of_scalars>.
@@ -4283,11 +4285,13 @@ BoUpSLP::getReorderingData(const TreeEntry &TE, bool TopToBottom) {
           return std::move(Order);
       }
     }
-    if (std::optional<OrdersType> CurrentOrder = findReusedOrderedScalars(TE))
-      return CurrentOrder;
+    if (isSplat(TE.Scalars))
+      return std::nullopt;
     if (TE.Scalars.size() >= 4)
       if (std::optional<OrdersType> Order = findPartiallyOrderedLoads(TE))
         return Order;
+    if (std::optional<OrdersType> CurrentOrder = findReusedOrderedScalars(TE))
+      return CurrentOrder;
   }
   return std::nullopt;
 }
@@ -4743,7 +4747,7 @@ void BoUpSLP::reorderBottomToTop(bool IgnoreReorder) {
           continue;
         if (!OpTE->ReuseShuffleIndices.empty() && !GathersToOrders.count(OpTE))
           continue;
-        const auto &Order = [OpTE, &GathersToOrders]() -> const OrdersType & {
+        const auto Order = [&]() -> const OrdersType {
           if (OpTE->State == TreeEntry::NeedToGather ||
               !OpTE->ReuseShuffleIndices.empty())
             return GathersToOrders.find(OpTE)->second;
@@ -4775,8 +4779,7 @@ void BoUpSLP::reorderBottomToTop(bool IgnoreReorder) {
           OrdersUses.insert(std::make_pair(Order, 0)).first->second += NumOps;
         }
         auto Res = OrdersUses.insert(std::make_pair(OrdersType(), 0));
-        const auto &&AllowsReordering = [IgnoreReorder, &GathersToOrders](
-                                            const TreeEntry *TE) {
+        const auto AllowsReordering = [&](const TreeEntry *TE) {
           if (!TE->ReorderIndices.empty() || !TE->ReuseShuffleIndices.empty() ||
               (TE->State == TreeEntry::Vectorize && TE->isAltShuffle()) ||
               (IgnoreReorder && TE->Idx == 0))
@@ -9394,6 +9397,8 @@ BoUpSLP::isGatherShuffledSingleRegisterEntry(
   } else {
     TEInsertBlock = TEInsertPt->getParent();
   }
+  if (!DT->isReachableFromEntry(TEInsertBlock))
+    return std::nullopt;
   auto *NodeUI = DT->getNode(TEInsertBlock);
   assert(NodeUI && "Should only process reachable instructions");
   SmallPtrSet<Value *, 4> GatheredScalars(VL.begin(), VL.end());