https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101718
--- Comment #1 from Iain Sandoe <iains at gcc dot gnu.org> ---
(In reply to Matt Jacobson from comment #0)
> When a method returns a type that the platform ABI says is returned in
> memory, the Objective-C frontend (for the NeXT runtime ABIs) emits a call to
> `objc_msgSend_stret`; the `_stret` variant of the message dispatcher knows
> to look at the *second* argument for `self`, and so on, since the first
> argument is the pointer to where the return value will go.
>
> On some platforms, `_Complex double` is too large to be returned through
> registers, so it's returned through memory.
can you give me some idea of the platform? it would help with testing at least
(assuming that there is a suitable machine on the cfarm).
Having said that, there could be some types for which this would fire even on
Darwin.
> But the Objective-C frontend still insists on using `objc_msgSend`, not
> `objc_msgSend_stret`.
>
> `objc_msgSend` is thoroughly confused when the first argument, which it
> expects to be `self`, is actually a pointer to garbage-filled stack.
>
> I believe this happens because this check:
>
> ```
> /* If we are returning a struct in memory, and the address
> of that memory location is passed as a hidden first
> argument, then change which messenger entry point this
> expr will call. NB: Note that sender_cast remains
> unchanged (it already has a struct return type). */
> if (!targetm.calls.struct_value_rtx (0, 0)
> && (TREE_CODE (ret_type) == RECORD_TYPE
> || TREE_CODE (ret_type) == UNION_TYPE)
> && targetm.calls.return_in_memory (ret_type, 0))
> {
> ```
>
> limits the use of `stret` to record/union types. Primitive types that are
> returned in memory should also be made to use `stret` (the name's meaning
> notwithstanding).
makes sense, but the fix might be interesting given the "NB: Note that
sender_cast remains unchanged (it already has a struct return type)." which
would no longer be true for a primitive type.
