[llvm] [SLP]Represent SLP graph as a tree (PR #126771)

[Simon Pilgrim via llvm-commits]

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@@ -5951,6 +5985,67 @@ static void combineOrders(MutableArrayRef<unsigned> Order,
   }
 }
 
+bool BoUpSLP::isProfitableToReorder() const {
+  constexpr unsigned TinyVF = 2;
+  constexpr unsigned TinyTree = 10;
+  if (VectorizableTree.size() <= TinyTree)
+    return true;
+  if (VectorizableTree.front()->hasState() &&
+      !VectorizableTree.front()->isGather() &&
+      (VectorizableTree.front()->getOpcode() == Instruction::Store ||
+       VectorizableTree.front()->getOpcode() == Instruction::PHI ||
+       (VectorizableTree.front()->getVectorFactor() == TinyVF &&
+        (VectorizableTree.front()->getOpcode() == Instruction::PtrToInt ||
+         VectorizableTree.front()->getOpcode() == Instruction::ICmp))) &&
+      VectorizableTree.front()->ReorderIndices.empty()) {
+    constexpr unsigned PhiOpsLimit = 12;
+    // Check if the tree has only single store and single (unordered) load node,
+    // other nodes are phis or geps/binops, combined with phis, and/orsingle
+    // gather load node
+    bool HasPhis = false;
+    if (VectorizableTree.front()->getOpcode() == Instruction::PHI &&
+        VectorizableTree.front()->Scalars.size() == TinyVF &&
+        VectorizableTree.front()->getNumOperands() > PhiOpsLimit)
+      return false;
+    bool HasLoad = true;
+    unsigned GatherLoads = 0;
+    for (const std::unique_ptr<TreeEntry> &TE :
+         ArrayRef(VectorizableTree).drop_front()) {
+      if (!TE->hasState()) {
+        if (all_of(TE->Scalars, IsaPred<Constant, PHINode>) ||
+            all_of(TE->Scalars, IsaPred<BinaryOperator, PHINode>))
+          continue;
+        if (VectorizableTree.front()->Scalars.size() == TinyVF &&
+            any_of(TE->Scalars, IsaPred<PHINode, GEPOperator>))
+          continue;
+        return true;
+      }
+      if (TE->getOpcode() == Instruction::Load && TE->ReorderIndices.empty()) {
+        if (!TE->isGather()) {
+          HasLoad = false;
+          continue;
+        }
+        if (HasLoad)
+          return true;
+        ++GatherLoads;
+        if (GatherLoads >= 2)
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RKSimon wrote:

Pull out the magic number?

https://github.com/llvm/llvm-project/pull/126771