[llvm] [RISCV] Fix incorrect fixed vector lowering for VECTOR_DEINTERLEAVE (PR #207254)

[Min-Yih Hsu via llvm-commits]

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@@ -13284,27 +13271,62 @@ SDValue RISCVTargetLowering::lowerVECTOR_DEINTERLEAVE(SDValue Op,
   }
 
   // Store with unit-stride store and load it back with segmented load.
+  SDValue Mask, VL;
   MVT XLenVT = Subtarget.getXLenVT();
-  auto [Mask, VL] = getDefaultScalableVLOps(VecVT, DL, DAG, Subtarget);
-  SDValue Passthru = DAG.getUNDEF(ConcatVT);
-
-  // Allocate a stack slot.
-  Align Alignment = DAG.getReducedAlign(VecVT, /*UseABI=*/false);
-  SDValue StackPtr =
-      DAG.CreateStackTemporary(ConcatVT.getStoreSize(), Alignment);
   auto &MF = DAG.getMachineFunction();
-  auto FrameIndex = cast<FrameIndexSDNode>(StackPtr.getNode())->getIndex();
-  auto PtrInfo = MachinePointerInfo::getFixedStack(MF, FrameIndex);
+  SDValue Chain = DAG.getEntryNode();
+  Align Alignment = DAG.getReducedAlign(VecVT, /*UseABI=*/false);
+  SDValue StackPtr;
+  MachinePointerInfo PtrInfo;
+  if (IsFixedVector) {
+    // Calculating the stack size.
+    ElementCount ActualConcatEC =
+        VecVT.getVectorElementCount().multiplyCoefficientBy(Factor);
+    EVT ConcatEVT = EVT::getVectorVT(
+        *DAG.getContext(), VecVT.getVectorElementType(), ActualConcatEC);
+    StackPtr = DAG.CreateStackTemporary(ConcatEVT.getStoreSize(), Alignment);
+    auto FrameIndex = cast<FrameIndexSDNode>(StackPtr.getNode())->getIndex();
+    PtrInfo = MachinePointerInfo::getFixedStack(MF, FrameIndex);
+
+    // If this is a fixed vector, instead of using the concat vector, we simply
+    // store each fixed vector operand directly onto the stack, individually.
+    // The reason being that if the fixed vector is (much) small than the
+    // container vector, we will be wasting space on stack.
+    TypeSize VecSize = VecVT.getStoreSize();
+    SDValue BasePtr = StackPtr;
+    MachinePointerInfo PI = PtrInfo;
+    for (auto [Idx, FieldOp] : enumerate(Op->op_values())) {
+      if (Idx) {
+        // Advance the pointer.
+        BasePtr = DAG.getObjectPtrOffset(DL, BasePtr, VecSize);
+        PI = PI.getWithOffset(VecSize);
+      }
+      Chain = DAG.getStore(Chain, DL, FieldOp, BasePtr, PI, Alignment);
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mshockwave wrote:

Done.

https://github.com/llvm/llvm-project/pull/207254