[llvm-dev] How to implement lowerReturn for poring GlobalISel to RISCV?

[Leslie Zhai via llvm-dev]

Hi Alex,

Sorry to bother you for the holidays!

I am stuck at CC_RISCV[1] you removed RetCC_RISCV32 and CC_RISCV32 from 
RISCVCallingConv.td and implemented a custom calling convention[2] 
function owing to TableGen-based calling convention definitions to lack 
flexibility and require substantial boilerplate when you reach their 
limitations.

I asked the similar question[3] in the mailing list before, and Diana 
suggested that having a CCAssignFn available would make it easier to use 
the existing infrastructure. Because ValueHandler needs a CCAssignFn 
varaible for handling return not void value in lowerReturn.

Please lead me to give me some direction, thanks a lot!

[1] https://reviews.llvm.org/D39898

[2] 
https://github.com/riscv/riscv-elf-psabi-doc/blob/master/riscv-elf.md#procedure-calling-convention

[3] http://lists.llvm.org/pipermail/llvm-dev/2017-November/119357.html


在 2017年12月21日 18:11, Alex Bradbury 写道:
> On 21 December 2017 at 09:05, Leslie Zhai <lesliezhai at llvm.org.cn> wrote:
>> Hi Alex,
>>
>> Thanks for your teaching!
>>
>> I only implemented GlobalISel skeleton for RISCV target, built with no
>> errors, is it suitable to review code now as Initial porting or wait for
>> more APIs (for example: lowerReturn, getStackAddress) implemented?
>  From my perspective, I think it would be useful to get a little more
> confidence about what you've implemented by at least adding support
> for lowering simple ALU operations. That would make it easier for
> someone who isn't an expert in GlobalISel (such as me) to review.
>
>> I use `a return from a void function` testcase:
>> <snip>
> Based on your follow-up message, it seems you got this working.
> Although comparing to gcc can be useful, I'd suggest that comparing to
> RISC-V SelectionDAGISel may be more useful. e.g. just using llc and
> -print-after-all or -debug-only=isel to see how the current codegen
> works. The existing tests in test/Codegen/RISCV should also be useful.
>
> Best,
>
> Alex

-- 
Regards,
Leslie Zhai - https://reviews.llvm.org/p/xiangzhai/