[llvm-dev] first class types

[Alexandre Isoard via llvm-dev]

Ah, that's why Clang is obsessively pushing them into return by reference?

On Thu, May 24, 2018 at 6:29 PM, whitequark <whitequark at whitequark.org>
wrote:

> On 2018-05-25 00:39, Alexandre Isoard via llvm-dev wrote:
>
>> Hello,
>>
>> I see here: https://llvm.org/docs/LangRef.html#ret-instruction
>>
>> That the return instruction must only return values of first class
>> types, which would exclude struct and arrays. But some llvm
>> instrinsics do return struct, and it does not seems to be enforced on
>> any function.
>>
>> Is that restriction lifted and the documentation not up to date? Can
>> we return arrays?
>> I see the same restriction for select. Can/should we lift it too?
>>
>
> In practice, you can return structs and arrays, and this while you stay
> within the optimizer, but how targets handle this is very variable.
> X86 internally lowers it to sret or something very similar to sret
> whereas lesser used targets (think MSP430) may outright assert.
>
> My understanding is that calling an intrinsic that returns a struct
> is defined (and never needs a ret instruction), but returning a struct
> from user code (which does need a ret instruction) is not, which is
> why LangRef is written like that.
>
> --
> whitequark
>



-- 
*Alexandre Isoard*
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