[llvm] [NVPTX] fold movs into loads and stores (PR #144581)

[Princeton Ferro via llvm-commits]

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@@ -5047,26 +5043,229 @@ PerformFADDCombineWithOperands(SDNode *N, SDValue N0, SDValue N1,
   return SDValue();
 }
 
-static SDValue PerformStoreCombineHelper(SDNode *N, std::size_t Front,
-                                         std::size_t Back) {
+/// Combine extractelts into a load by increasing the number of return values.
+static SDValue
+combineUnpackingMovIntoLoad(SDNode *N, TargetLowering::DAGCombinerInfo &DCI) {
+  // Don't run this optimization before the legalizer
+  if (DCI.isBeforeLegalize())
+    return SDValue();
+
+  EVT ElemVT = N->getValueType(0);
+  if (!Isv2x16VT(ElemVT))
+    return SDValue();
+
+  // Check whether all outputs are either used by an extractelt or are
+  // glue/chain nodes
+  if (!all_of(N->uses(), [&](SDUse &U) {
+        return U.getValueType() != ElemVT ||
+               (U.getUser()->getOpcode() == ISD::EXTRACT_VECTOR_ELT &&
+                // also check that the extractelt is used if this is an
+                // ISD::LOAD, otherwise it may be optimized by something else
+                (N->getOpcode() != ISD::LOAD || !U.getUser()->use_empty()));
+      }))
+    return SDValue();
+
+  auto *LD = cast<MemSDNode>(N);
+  EVT MemVT = LD->getMemoryVT();
+  SDLoc DL(LD);
+
+  // the new opcode after we double the number of operands
+  NVPTXISD::NodeType Opcode;
+  SmallVector<SDValue> Operands(LD->ops());
+  switch (LD->getOpcode()) {
+  // Any packed type is legal, so the legalizer will not have lowered ISD::LOAD
+  // -> NVPTXISD::Load. We have to do it here.
+  case ISD::LOAD:
+    Opcode = NVPTXISD::LoadV2;
+    {
+      Operands.push_back(DCI.DAG.getIntPtrConstant(
+          cast<LoadSDNode>(LD)->getExtensionType(), DL));
+      Align Alignment = LD->getAlign();
+      const auto &TD = DCI.DAG.getDataLayout();
+      Align PrefAlign =
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Prince781 wrote:

Good catch.

https://github.com/llvm/llvm-project/pull/144581