[llvm] [MachineInstr] add insert method for variadic instructions (PR #67699)

[Matthias Braun via llvm-commits]

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@@ -2475,3 +2475,45 @@ MachineInstr::getFirst5RegLLTs() const {
       Reg2, getRegInfo()->getType(Reg2), Reg3, getRegInfo()->getType(Reg3),
       Reg4, getRegInfo()->getType(Reg4));
 }
+
+void MachineInstr::insert(mop_iterator It, ArrayRef<MachineOperand> Ops) {
+  if (!It || Ops.empty())
+    return;
+
+  // Do one pass to untie operands.
+  DenseMap<unsigned, unsigned> TiedOpIndices;
+  for (const MachineOperand &MO : operands()) {
+    if (MO.isReg() && MO.isTied()) {
+      unsigned OpNo = getOperandNo(&MO);
+      unsigned TiedTo = findTiedOperandIdx(OpNo);
+      TiedOpIndices[OpNo] = TiedTo;
+      untieRegOperand(OpNo);
+    }
+  }
+
+  assert(It->getParent() == this && "iterator points to operand of other inst");
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MatzeB wrote:

Maybe move earlier so it is checked even if `Ops.empty()` ? (though no strong opinion on this one)

https://github.com/llvm/llvm-project/pull/67699