[llvm] [SLP]Support revectorization of the previously vectorized scalars (PR #133091)

[Alexey Bataev via llvm-commits]

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@@ -9253,14 +9253,44 @@ void BoUpSLP::buildTree_rec(ArrayRef<Value *> VL, unsigned Depth,
   // We now know that this is a vector of instructions of the same type from
   // the same block.
 
-  // Check that none of the instructions in the bundle are already in the tree.
-  for (Value *V : VL) {
-    if ((!IsScatterVectorizeUserTE && !isa<Instruction>(V)) ||
-        doesNotNeedToBeScheduled(V))
-      continue;
-    if (isVectorized(V)) {
-      LLVM_DEBUG(dbgs() << "SLP: The instruction (" << *V
-                        << ") is already in tree.\n");
+  // Check that none of the instructions in the bundle are already in the tree
+  // and the node may be not profitable for the vectorization as the small
+  // alternate node.
+  if (S && S.isAltShuffle()) {
+    auto GetNumVectorizedExtracted = [&]() {
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alexey-bataev wrote:

Moving this check into a separate function is meaningless. Better to move the checks, resulting in gather/buildvector, into a separate function, but better to do it in a separate patch.

https://github.com/llvm/llvm-project/pull/133091