[X86][NFC] Add documentation for methods in X86InstrInfo.h

                            const MachineInstr &OI, bool *IsSwapped,

                            int64_t *ImmDelta) const;

  /// Commute operands of \p MI for memory fold.

  ///

  /// \param Idx1 the index of operand to be commuted.

  ///

  /// \returns the index of operand that is commuted with \p Idx1. If the method

  /// fails to commute the operands, it will return \p Idx1.

  unsigned commuteOperandsForFold(MachineInstr &MI, unsigned Idx1) const;

  /// Undo the commute of operands of \p MI at index \p Idx1 and index \p Idx2.

  void UndoCommuteForFold(MachineInstr &MI, unsigned Idx1, unsigned Idx2) const;

};

} // namespace llvm