-
CorePrep already had a check to prevent it from eta-reducing Ids that respond true to hasNoBinding (foreign calls, constructors for unboxed sums and products, and Ids with compulsory unfoldings). It did not, however, consider join points as ids that 'must be saturated'. Checking whether the Id responds True to 'isJoinId' should prevent CorePrep from turning saturated jumps like the following (from #17429) into undersaturated ones: (\ eta_XP -> join { mapped_s1vo _ = lvl_s1vs } in jump mapped_s1vo eta_XP) (cherry picked from commit de6bbdf2)
61fe6c68