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

[Rajveer Singh Bharadwaj via llvm-commits]

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@@ -2988,6 +2989,240 @@ 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;
+  Value *InitEEV = nullptr;
+
+  unsigned int CommonCallOp = 0, CommonBinOp = 0;
+
+  bool IsFirstCallOrBinInst = true;
+  bool ShouldBeCallOrBinInst = true;
+
+  SmallVector<Value *, 3> PrevVecV(3, nullptr);
+  int64_t ShuffleMaskHalf = -1, ExpectedShuffleMaskHalf = 1;
+  int64_t VecSize = -1;
+
+  Value *VecOp;
+  if (!match(&I, m_ExtractElt(m_Value(VecOp), m_Zero())))
+    return false;
+
+  auto *FVT = dyn_cast<FixedVectorType>(VecOp->getType());
+  if (!FVT)
+    return false;
+
+  VecSize = FVT->getNumElements();
+  if (VecSize < 2 || (VecSize % 2) != 0)
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Rajveer100 wrote:

At the moment it works for even integers (not limited to powers of 2). For odd, I will need to check again for a suitable pattern and resolve the parity.

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