[LLVMdev] struct passing on X86-64

[David A. Greene]

Duncan Sands <baldrick at free.fr> writes:

>> Yep.  There are lots of corner cases that the frontend MUST handle
>> because LLVM does not have the necessary infrastructure.
>
> I think it's more like: because LLVM doesn't have the necessary information.

True.

> Due to LLVM using structural equivalence, all kinds of types that are
> different in the original language end up being the same type in LLVM.
> Chris once explained to me, IIRC, that the ABI is defined in terms of
> the original language types, and unfortunately some ABI's require
> different handling for types that are structurally equivalent.

Just so I understand this better, for which ABIs is this the case?  It's
not for x86_64.  ARM, perhaps?

> See PR4246 for a plan to have generic helper codes for ABI lowering.

It seems a bit complicated to me.  Wouldn't it be simpler to just encode
the language type information in metadata, or, if metadata isn't
appropriate because it can be dropped, in some language information
piece within Type?  Then the target ABI stuff can know exactly what to
do and we won't have various other pieces all trying to figure out the
same stuff.

                             -Dave