I found one of the problems with #11444, but I don't know how to fix it. The problem is that the desugarer is generating this function: ptrEq [InlPrag=NOINLINE] :: forall a_a1wc. a_a1wc -> a_a1wc -> Bool [LclIdX, Str=DmdType] ptrEq = \ (@ a_a1Ts) (x_a1we :: a_a1Ts) (y_a1wf :: a_a1Ts) -> case x_a1we of x_X1wq { __DEFAULT -> case y_a1wf of y_X1ws { __DEFAULT -> == @ Int GHC.Classes.$fEqInt (case reallyUnsafePtrEquality# @ a_a1Ts x_X1wq y_X1ws of wild_00 { __DEFAULT -> GHC.Types.I# wild_00 }) (GHC.Types.I# 1#) } } Which is lint-safe. Then, the optimizer is transforming this into: ptrEq [InlPrag=NOINLINE] :: forall a_a1wc. a_a1wc -> a_a1wc -> Bool [LclIdX, Arity=2, Str=DmdType, Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True, WorkFree=True, Expandable=True, Guidance=IF_ARGS [20 20] 71 0}] ptrEq = \ (@ a_a1Ts) (x_a1we :: a_a1Ts) (y_a1wf :: a_a1Ts) -> case x_a1we of x_X1wq { __DEFAULT -> case y_a1wf of y_X1ws { __DEFAULT -> eqInt (I# (reallyUnsafePtrEquality# @ a_a1Ts x_X1wq y_X1ws)) (I# 1#) } } The problem with this, according to the linter, is the argument of I# is not OK-for-speculation (the expression `reallyUnsafePtrEquality# @ a_a1Ts x_X1wq y_X1ws`). The reason is because arguments of `reallyUnsafePtrEquality#` are not OK-for-speculation, because their types are polymorphic, and variables with polymorphic types are not OK for speculation. However, I think this expression should be OK-for-speculation, because it can't fail, the primop is not out-of-line etc. I think all the requirements for being OK for speculation hold here. So my questions are: - Does that look like a correct optimization transformation? (it looked OK to me, but wanted to make sure) - Am I right that this expression should be OK for speculation? - What's a good way to make this code lint-safe? Thanks..