[llvm] [VectorCombine] New folding pattern for extract/binop/shuffle chains (PR #145232)

[Yingwei Zheng via llvm-commits]

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@@ -2988,6 +2989,241 @@ bool VectorCombine::foldShuffleFromReductions(Instruction &I) {
   return foldSelectShuffle(*Shuffle, true);
 }
 
+bool VectorCombine::foldShuffleChainsToReduce(Instruction &I) {
+  auto *EEI = dyn_cast<ExtractElementInst>(&I);
+  if (!EEI)
+    return false;
+
+  std::queue<Value *> InstWorklist;
+  InstructionCost OrigCost = 0;
+
+  Value *InitEEV = nullptr;
+
+  unsigned int CommonCallOp = 0;
+  Instruction::BinaryOps CommonBinOp = Instruction::BinaryOpsEnd;
+
+  bool IsFirstCallOrBinInst = true;
+  bool ShouldBeCallOrBinInst = true;
+
+  SmallVector<Value *, 3> PrevVecV(3, nullptr);
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dtcxzyw wrote:

I cannot understand what this array is used for. You always access its elements with constant indices, so these elements seem to have different meanings. Can you add some comments to explain the meaning of each element?


https://github.com/llvm/llvm-project/pull/145232