[llvm] [RISCV] Make InitUndef handle undef operand (PR #65755)

[Piyou Chen via llvm-commits]

================
@@ -134,53 +134,32 @@ static bool isEarlyClobberMI(MachineInstr &MI) {
   });
 }
 
-bool RISCVInitUndef::handleImplicitDef(MachineBasicBlock &MBB,
-                                       MachineBasicBlock::iterator &Inst) {
-  assert(Inst->getOpcode() == TargetOpcode::IMPLICIT_DEF);
-
-  Register Reg = Inst->getOperand(0).getReg();
-  if (!Reg.isVirtual())
-    return false;
-
-  bool HasOtherUse = false;
-  SmallVector<MachineOperand *, 1> UseMOs;
-  for (MachineOperand &MO : MRI->use_nodbg_operands(Reg)) {
-    if (isEarlyClobberMI(*MO.getParent())) {
-      if (MO.isUse() && !MO.isTied())
-        UseMOs.push_back(&MO);
-      else
-        HasOtherUse = true;
-    }
-  }
-
-  if (UseMOs.empty())
-    return false;
-
-  LLVM_DEBUG(
-      dbgs() << "Emitting PseudoRVVInitUndef for implicit vector register "
-             << Reg << '\n');
-
-  const TargetRegisterClass *TargetRegClass =
-    getVRLargestSuperClass(MRI->getRegClass(Reg));
-  unsigned Opcode = getUndefInitOpcode(TargetRegClass->getID());
-
-  Register NewDest = Reg;
-  if (HasOtherUse) {
-    NewDest = MRI->createVirtualRegister(TargetRegClass);
-    // We don't have a way to update dead lanes, so keep track of the
-    // new register so that we avoid querying it later.
-    NewRegs.insert(NewDest);
+static bool findImplictDefMIFromReg(Register Reg, MachineRegisterInfo *MRI) {
+  for (auto &DefMI : MRI->def_instructions(Reg)) {
+    if (DefMI.getOpcode() == TargetOpcode::IMPLICIT_DEF)
+      return true;
   }
-  BuildMI(MBB, Inst, Inst->getDebugLoc(), TII->get(Opcode), NewDest);
+  return false;
+}
 
-  if (!HasOtherUse)
-    Inst = MBB.erase(Inst);
+bool RISCVInitUndef::handleReg(MachineInstr *MI) {
+  bool Changed = false;
+  for (auto &UseMO : MI->uses()) {
+    if (!UseMO.isReg())
+      continue;
+    if (UseMO.isTied())
+      continue;
+    if (!UseMO.getReg().isVirtual())
+      continue;
+    if (!isVectorRegClass(UseMO.getReg()))
+      continue;
+    if (UseMO.getReg() == 0)
----------------
BeMg wrote:

You're right. `$noreg` is not belong to virtual register. 

Remove the `reg == 0` . 

https://github.com/llvm/llvm-project/pull/65755