llvm dev - Dec 2009 - [LLVMdev] Win64 Calling Convention problem

Hello
> I don't know. I feel reluctant to generate different IRs for Win32 and
> for Win64.
Unfortunately, you should. Think about differences and between
_Complex type and struct {double, double}.
>From LLVM's point of view these are same types, however many ABIs have
special rules for passing / returning _Complex,
this is possible to handle in frontend only.
> Since the C calling convention is the default for LLVM functions, I
> thought that it would map to *the* Win64 calling convention (since
> cdecl, fastcall and stdcall are all the same) when a 64-bit build was
> used. This is quite confusing ...
Yes, default calling convention is C. But you're not using an
ABI-compliant C compiler to generate the IR.

-- 
With best regards, Anton Korobeynikov
Faculty of Mathematics and Mechanics, Saint Petersburg State University

Hello, Stephan
> I didn't know about exceptions like _Complex that you mentioned. The
> only way to support them is to place the burden of correct parameter
> passing on the front-end, I understand that now.
Right. Especially when ABI dictates quite "weird" rules (read e.g.
x86-64 ABI or ARM EABI).
We do support one "exception" though for win64 - __m128 vectors. This
was done since they are
native types and thus do not get changed by type legalizer. I have no
idea why MS decided not to
pass then in registers... This is silly...
> So, today I created a new transformation pass that makes sure that
> LLVM IR, which works alright with the default Win32 calling
> conventions, also plays nice with Win64 code within the limited scope
> of my language (that requires packing of aggregates of sizes 8, 16,
> 32, and 64-bits into an integer argument, and passing of larger
> aggregates by reference).
Sounds like pretty sane approach :)

-- 
With best regards, Anton Korobeynikov
Faculty of Mathematics and Mechanics, Saint Petersburg State University