[llvm] [SLP]Improve/fix subvectors in gather/buildvector nodes handling (PR #104144)

[Simon Pilgrim via llvm-commits]

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@@ -8361,8 +8367,49 @@ getGEPCosts(const TargetTransformInfo &TTI, ArrayRef<Value *> Ptrs,
 
 void BoUpSLP::transformNodes() {
   constexpr TTI::TargetCostKind CostKind = TTI::TCK_RecipThroughput;
-  for (std::unique_ptr<TreeEntry> &TE : VectorizableTree) {
-    TreeEntry &E = *TE;
+  // The tree may grow here, so iterate over nodes, built before.
+  for (unsigned Idx : seq<unsigned>(VectorizableTree.size())) {
+    TreeEntry &E = *VectorizableTree[Idx];
+    if (E.isGather()) {
+      ArrayRef<Value *> VL = E.Scalars;
+      const unsigned Sz = getVectorElementSize(VL.front());
+      unsigned MinVF = getMinVF(2 * Sz);
+      if (VL.size() <= 2 ||
+          (E.getOpcode() &&
+           (E.isAltShuffle() || E.getOpcode() != Instruction::Load)))
+        continue;
+      // Try to find vectorizable sequences and transform them into a serie of
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RKSimon wrote:

serie -> series

https://github.com/llvm/llvm-project/pull/104144