llvm dev - Dec 2010 - [LLVMdev] stack alignment restriction

Hi
   Is there a way to enforce a different alignment on vales on stack
as compared to other basic types.  Particularly, i would like
characters to be stored at 2 byte boundary.

thanks
dz

On Dec 28, 2010, at 4:02 PM, drizzle drizzle wrote:
> Hi
>   Is there a way to enforce a different alignment on vales on stack
> as compared to other basic types.  Particularly, i would like
> characters to be stored at 2 byte boundary.
> 
Check out examples in the lib/Target/* directories. For instance in
X86CallingConv.td, we have things like this:

def CC_X86_64_C : CallingConv<[
...
  // __m64 vectors get 8-byte stack slots that are 8-byte aligned.
  CCIfType<[x86mmx,v1i64], CCAssignToStack<8, 8>>
}

The second parameter to CCAssigneToStack is the alignment for that type.

-bw

Thanks for the answer..
A followup question - Is this already taken into consideration when
generating address calculation offset etc or would this need to be
specially taken care?
I am assuming all load/stores also would need to be custom lowered.

thanks
dz

On Wed, Dec 29, 2010 at 5:45 AM, Bill Wendling <wendling at apple.com>
wrote:
> On Dec 28, 2010, at 4:02 PM, drizzle drizzle wrote:
>
>> Hi
>>   Is there a way to enforce a different alignment on vales on stack
>> as compared to other basic types.  Particularly, i would like
>> characters to be stored at 2 byte boundary.
>>
> Check out examples in the lib/Target/* directories. For instance in
X86CallingConv.td, we have things like this:
>
> def CC_X86_64_C : CallingConv<[
> ...
>  // __m64 vectors get 8-byte stack slots that are 8-byte aligned.
>  CCIfType<[x86mmx,v1i64], CCAssignToStack<8, 8>>
> }
>
> The second parameter to CCAssigneToStack is the alignment for that type.
>
> -bw
>
>