[RFC] An ABI lowering library for LLVM

[nikic]

@efriedma-quic

If you’re suggesting that we only need to look at canonical types, the answer is no, we can’t do that. Non-canonical types are, unfortunately, relevant in weird ways due to the way we handle certain attributes. Maybe we can distill out some lowered representation, but what happens if the representation needs to change for some future target?

Could you please share an example where non-canonical types matters for the call ABI?

@rjmccall

it is not true that const in other positions never affects the ABI (e.g. MSVC returns struct { int x; } in registers but struct { const int x; } indirectly).

Interesting case. Is this handled as part of RecordArgPassingKind / RecordArgABI or a separate rule? If the former, we still wouldn’t need this in the ABI type system, if we approach C++ as described in my previous comment (making it an additional input).