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

[via llvm-commits]

================
@@ -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 = [&]() {
----------------
hiraditya wrote:

Should we outline this to a separate function? This function is already getting bigger.

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