[llvm] [X86] Combine `store + vselect` to `masked_store` (PR #145176)

[Phoebe Wang via llvm-commits]

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@@ -53403,6 +53404,76 @@ static SDValue combineMaskedStore(SDNode *N, SelectionDAG &DAG,
   return SDValue();
 }
 
+static SDValue foldToMaskedStore(StoreSDNode *Store, SelectionDAG &DAG,
+                                 const SDLoc &Dl,
+                                 const X86Subtarget &Subtarget) {
+  using namespace llvm::SDPatternMatch;
+
+  if (!Subtarget.hasAVX() && !Subtarget.hasAVX2() && !Subtarget.hasAVX512())
+    return SDValue();
+
+  if (!Store->isSimple() || Store->isTruncatingStore())
+    return SDValue();
+
+  SDValue StoredVal = Store->getValue();
+  SDValue StorePtr = Store->getBasePtr();
+  SDValue StoreOffset = Store->getOffset();
+  EVT VT = Store->getMemoryVT();
+  const TargetLowering &TLI = DAG.getTargetLoweringInfo();
+
+  if (!TLI.isTypeLegal(VT) || !TLI.isOperationLegalOrCustom(ISD::MSTORE, VT))
+    return SDValue();
+
+  SDValue Mask, TrueVec, LoadCh;
+  if (!sd_match(StoredVal,
+                m_VSelect(m_Value(Mask), m_Value(TrueVec),
+                          m_Load(m_Value(LoadCh), m_Specific(StorePtr),
+                                 m_Specific(StoreOffset)))))
+    return SDValue();
+
+  LoadSDNode *Load = cast<LoadSDNode>(StoredVal.getOperand(2));
+  if (!Load || !Load->isSimple())
+    return SDValue();
+
+  auto IsSafeToFold = [](StoreSDNode *Store, LoadSDNode *Load) {
+    std::queue<SDValue> Worklist;
+
+    Worklist.push(Store->getChain());
+
+    while (!Worklist.empty()) {
+      SDValue Chain = Worklist.front();
+      Worklist.pop();
+
+      SDNode *Node = Chain.getNode();
+      if (!Node)
+        return false;
+
+      if (Node == Load)
+        return true;
+
+      if (const auto *MemNode = dyn_cast<MemSDNode>(Node))
+        if (!MemNode->isSimple() || MemNode->writeMem())
+          return false;
+
+      if (Node->getOpcode() == ISD::TokenFactor) {
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phoebewang wrote:

Is there a test for it?

https://github.com/llvm/llvm-project/pull/145176