> I can't see how this can work with LTO. We need a middle-end way > to represent the alias relation of those types. At least I can't see how > your simple patch covers all cases here?
It covers what I think is the most prominent case (unconstrained array types), the other cases are far less annoying in practice. > With LTO we preserve TYPE_ALIAS_SET == 0, so another way to > fix this (and which I'd like more) is to do your patch in the Ada frontend, > that is, use alias-set zero for all types you relate if flag_lto. Really Big Hammer if you ask me. > Another way is to make LTO canonical type merging handle the > case of type_contains_placeholder_p "better", that is by treating > two types with those equivalent more easily. For arrays this simply > means hashing and comparing non-constant TYPE_DOMAIN the > same / as equal. There is already some code handling PLACEHODER_EXPR > special, but it doesn't seem to be enough (why in this case)? Yes, gimple_canonical_types_compatible_p will return true for a couple of unconstrained (i.e. type_contains_placeholder_p) array types with the same component type. The problem here is for an unconstrained array type and a constrained (regular) array type with the same component type. Can I modify gimple_canonical_types_compatible_p to return true in that case as well? -- Eric Botcazou
