[llvm] [RISCV][GISel] Support select vector load intrinsics (PR #160720)

[Craig Topper via llvm-commits]

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@@ -675,6 +681,109 @@ static void getOperandsForBranch(Register CondReg, RISCVCC::CondCode &CC,
   CC = getRISCVCCFromICmp(Pred);
 }
 
+bool RISCVInstructionSelector::selectIntrinsicWithSideEffects(
+    MachineInstr &I, MachineIRBuilder &MIB) const {
+  // Find the intrinsic ID.
+  unsigned IntrinID = cast<GIntrinsic>(I).getIntrinsicID();
+  // Select the instruction.
+  switch (IntrinID) {
+  default:
+    return false;
+  case Intrinsic::riscv_vlm:
+  case Intrinsic::riscv_vle:
+  case Intrinsic::riscv_vle_mask:
+  case Intrinsic::riscv_vlse:
+  case Intrinsic::riscv_vlse_mask: {
+    bool IsMasked = IntrinID == Intrinsic::riscv_vle_mask ||
+                    IntrinID == Intrinsic::riscv_vlse_mask;
+    bool IsStrided = IntrinID == Intrinsic::riscv_vlse ||
+                     IntrinID == Intrinsic::riscv_vlse_mask;
+    LLT VT = MRI->getType(I.getOperand(0).getReg());
+    unsigned Log2SEW = Log2_32(VT.getScalarSizeInBits());
+
+    // Result vector
+    const Register DstReg = I.getOperand(0).getReg();
+    const TargetRegisterClass *DstRC = getRegClassForTypeOnBank(
+        MRI->getType(DstReg), *RBI.getRegBank(DstReg, *MRI, TRI));
+    if (IsMasked)
+      DstRC = TRI.getNoV0RegClass(DstRC);
+    RBI.constrainGenericRegister(DstReg, *DstRC, *MRI);
+
+    // Sources
+    bool HasPassthruOperand = IntrinID != Intrinsic::riscv_vlm;
+    unsigned CurOp = 2;
+    SmallVector<SrcOp, 4> SrcOps; // Source registers.
+
+    // Passthru
+    if (HasPassthruOperand) {
+      auto PassthruReg = I.getOperand(CurOp++).getReg();
+      SrcOps.push_back(PassthruReg);
+      RBI.constrainGenericRegister(PassthruReg, *DstRC, *MRI);
+    } else {
+      auto UndefReg = MRI->createVirtualRegister(DstRC);
+      MIB.buildInstr(TargetOpcode::IMPLICIT_DEF).addDef(UndefReg);
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topperc wrote:

I think we're supposed to use NoRegister when there is no passthru. See `RISCVDAGToDAGISel::doPeepholeNoRegPassThru`

https://github.com/llvm/llvm-project/pull/160720