大般涅槃經義記 3.262

3.262

就初句中，「非苦為苦名曰顛倒」總以標舉，下釋其相非苦，如來解其所迷。生倒想者謂佛無常，彰其所立，無常故苦。

In the first clause, 'taking non-suffering as suffering is called inversion' generally designates it; below, it explains its characteristics. 'Non-suffering' is the Tathāgata, explaining what they are deluded about. 'Those who generate inverted notions' refers to [taking] the Buddha as impermanent, revealing what they assert: impermanent, therefore suffering.