This patch implements two related changes, both inspired by the discussion on Trac #13027, comment:23: * exprOkForSpeculation (op# a1 .. an), where op# is a primop, now skips over arguments ai of lifted type. See the comments at Note [Primops with lifted arguments] in CoreUtils. There is no need to treat dataToTag# specially any more. * dataToTag# is now treated as a can-fail primop. See Note [dataToTag#] in primops.txt.pp I don't expect this to have a visible effect on anything, but it's much more solid than before.
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