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

[Eli Friedman]

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.

-Eli