[cfe-commits] [llvm-commits] [PATCH] ARM ABI: handle varargs with vector types.

[Manman Ren]

On Oct 16, 2012, at 11:32 AM, Eli Friedman wrote:

> On Tue, Oct 16, 2012 at 11:10 AM, manman ren <mren at apple.com> wrote:
>> 
>> On Oct 15, 2012, at 5:59 PM, Eli Friedman <eli.friedman at gmail.com> wrote:
>> 
>>> On Mon, Oct 15, 2012 at 5:38 PM, Manman Ren <mren at apple.com> wrote:
>>>> 
>>>> On Oct 15, 2012, at 5:34 PM, Eli Friedman wrote:
>>>> 
>>>>> On Mon, Oct 15, 2012 at 5:26 PM, Manman Ren <mren at apple.com> wrote:
>>>>>> 
>>>>>> On Oct 15, 2012, at 5:11 PM, Eli Friedman wrote:
>>>>>> 
>>>>>>> On Mon, Oct 15, 2012 at 4:46 PM, manman ren <mren at apple.com> wrote:
>>>>>>>> 
>>>>>>>> The initial patch was updated and separated to two patches (attached).
>>>>>>>> 
>>>>>>>> The first patch will fix passing legal vector types as varargs:
>>>>>>>> We make sure the vector is correctly aligned before casting it to the vector type.
>>>>>>> 
>>>>>>> +  uint64_t Size = CGF.getContext().getTypeSize(Ty) / 8;
>>>>>>> +  uint64_t TyAlign = CGF.getContext().getTypeAlign(Ty) / 8;
>>>>>>> +
>>>>>>> +  // The ABI alignment for vectors is 8 for AAPCS and 4 for APCS.
>>>>>>> +  if (Ty->getAs<VectorType>() && Size >= 8) {
>>>>>>> +    if (getABIKind() == ARMABIInfo::AAPCS_VFP ||
>>>>>>> +        getABIKind() == ARMABIInfo::AAPCS)
>>>>>>> +      TyAlign = 8;
>>>>>>> +    else
>>>>>>> +      TyAlign = 4;
>>>>>>> +  }
>>>>>>> 
>>>>>>> We should be using the same rules here we do for argument passing.  In
>>>>>>> particular, for APCS, the argument-passing type alignment is
>>>>>>> unconditionally 4.  (This can have effects for structs marked with
>>>>>>> "__attribute__((aligned(16)))", etc.)
>>>>>> Is there an interface to query the argument-passing alignment?
>>>>> 
>>>>> Nothing cares about it other than the calling convention code, so
>>>>> there isn't a general API.  It's basically just "match whatever
>>>>> ARMABIInfo::classifyArgumentType does".
>>>> 
>>>> I don't see code in ARMABIInfo::classifyArgumentType that checks the argument-passing alignment.
>>>> The code in the patch is trying to match what the calling convention does in the backend:
>>> 
>>> Yes, it's a bit tricky because of the implicit contract between clang
>>> and the ARM backend... you basically have to combine the frontend and
>>> backend rules to figure out how the result is actually represented on
>>> the stack.  When you do that, it comes out to always 4 for APCS, and I
>>> think it comes out to min(max(naturalAlign, 4), 8) for AAPCS.
>> 
>> I think you are right, the patch is updated, please review again :]
> 
> +  if (Ty->getAs<VectorType>()) {
> 
> Why restrict the check to vector types?  (This check can have effects
> for other types, e.g. structs containing vectors.)
I want to make sure this patch only touches varargs with vector types.
For other types, we can handle those in a separate patch with additional testing cases.

Thanks,
Manman

> 
> +  if (Ty->getAs<VectorType>() &&
> 
> Same here.
> 
> -Eli