[SLP]Do not reorder top nodes if they do not require reordering.

No need to reorder the top nodes, if they are not stores or
insertelement instructions and each node should be analized only
once, when the bottom-to-top analysis is performed.
We still endup with extractelements for the top node scalars and
the final shuffle just adds an extra cost and currently
crashes the compiler for PHI nodes.

Differential Revision: https://reviews.llvm.org/D116760

Author: alexey-bataev

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -3307,9 +3307,14 @@ void BoUpSLP::reorderBottomToTop(bool IgnoreReorder) {
       MapVector<OrdersType, unsigned,
                 DenseMap<OrdersType, unsigned, OrdersTypeDenseMapInfo>>
           OrdersUses;
+      // Do the analysis for each tree entry only once, otherwise the order of
+      // the same node my be considered several times, though might be not
+      // profitable.
       SmallPtrSet<const TreeEntry *, 4> VisitedOps;
       for (const auto &Op : Data.second) {
         TreeEntry *OpTE = Op.second;
+        if (!VisitedOps.insert(OpTE).second)
+          continue;
         if (!OpTE->ReuseShuffleIndices.empty() ||
             (IgnoreReorder && OpTE == VectorizableTree.front().get()))
           continue;
@@ -3333,9 +3338,8 @@ void BoUpSLP::reorderBottomToTop(bool IgnoreReorder) {
         } else {
           ++OrdersUses.insert(std::make_pair(Order, 0)).first->second;
         }
-        if (VisitedOps.insert(OpTE).second)
-          OrdersUses.insert(std::make_pair(OrdersType(), 0)).first->second +=
-              OpTE->UserTreeIndices.size();
+        OrdersUses.insert(std::make_pair(OrdersType(), 0)).first->second +=
+            OpTE->UserTreeIndices.size();
         assert(OrdersUses[{}] > 0 && "Counter cannot be less than 0.");
         --OrdersUses[{}];
       }
@@ -8444,7 +8448,7 @@ bool SLPVectorizerPass::tryToVectorizeList(ArrayRef<Value *> VL, BoUpSLP &R,
       if (R.isTreeTinyAndNotFullyVectorizable())
         continue;
       R.reorderTopToBottom();
-      R.reorderBottomToTop();
+      R.reorderBottomToTop(!isa<InsertElementInst>(Ops.front()));
       R.buildExternalUses();
 
       R.computeMinimumValueSizes();

llvm/test/Transforms/SLPVectorizer/X86/reordered-top-scalars.ll

@@ -0,0 +1,43 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S --slp-vectorizer -mtriple=x86_64-unknown %s -slp-threshold=-5 | FileCheck %s
+
+define i32 @test(i32* %isec) {
+; CHECK-LABEL: @test(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[ARRAYIDX10:%.*]] = getelementptr inbounds i32, i32* [[ISEC:%.*]], i32 0
+; CHECK-NEXT:    [[TMP0:%.*]] = bitcast i32* [[ARRAYIDX10]] to <2 x i32>*
+; CHECK-NEXT:    [[TMP1:%.*]] = load <2 x i32>, <2 x i32>* [[TMP0]], align 8
+; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <2 x i32> [[TMP1]], <2 x i32> poison, <2 x i32> <i32 1, i32 0>
+; CHECK-NEXT:    [[TMP2:%.*]] = extractelement <2 x i32> [[TMP1]], i32 0
+; CHECK-NEXT:    [[TMP3:%.*]] = insertelement <2 x i32> poison, i32 [[TMP2]], i32 0
+; CHECK-NEXT:    [[TMP4:%.*]] = extractelement <2 x i32> [[TMP1]], i32 1
+; CHECK-NEXT:    [[TMP5:%.*]] = insertelement <2 x i32> [[TMP3]], i32 [[TMP4]], i32 1
+; CHECK-NEXT:    br i1 false, label [[BLOCK1:%.*]], label [[BLOCK3:%.*]]
+; CHECK:       block1:
+; CHECK-NEXT:    br i1 false, label [[BLOCK2:%.*]], label [[BLOCK3]]
+; CHECK:       block2:
+; CHECK-NEXT:    br label [[BLOCK3]]
+; CHECK:       block3:
+; CHECK-NEXT:    [[TMP6:%.*]] = phi <2 x i32> [ [[SHUFFLE]], [[BLOCK1]] ], [ [[SHUFFLE]], [[BLOCK2]] ], [ [[TMP5]], [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[TMP7:%.*]] = extractelement <2 x i32> [[TMP6]], i32 0
+; CHECK-NEXT:    [[TMP8:%.*]] = extractelement <2 x i32> [[TMP6]], i32 1
+; CHECK-NEXT:    [[TMP9:%.*]] = mul i32 [[TMP7]], [[TMP8]]
+; CHECK-NEXT:    ret i32 [[TMP9]]
+;
+entry:
+  %arrayidx10 = getelementptr inbounds i32, i32* %isec, i32 0
+  %0 = bitcast i32* %arrayidx10 to <2 x i32>*
+  %1 = load <2 x i32>, <2 x i32>* %0, align 8
+  %2 = extractelement <2 x i32> %1, i32 1
+  %3 = extractelement <2 x i32> %1, i32 0
+  br i1 false, label %block1, label %block3
+block1:
+  br i1 false, label %block2, label %block3
+block2:
+  br label %block3
+block3:
+  %4 = phi i32 [ %2, %block1 ], [ %2, %block2 ], [ %3, %entry ]
+  %5 = phi i32 [ %3, %block1 ], [ %3, %block2 ], [ %2, %entry ]
+  %6 = mul i32 %4, %5
+  ret i32 %6
+}