Return the registers and LLTs of the first three operands.
Declared in <llvm/CodeGen/MachineInstr.h>
<llvm/CodeGen/MachineInstr.h>
std::tuple<Register, LLT, Register, LLT, Register, LLT> getFirst3RegLLTs() const;
Tuple of (reg, LLT) pairs for the first three operands.