llvm dev - Nov 2013 - [LLVMdev] DAGCompiler::MergeConsecutiveStores Question

In DAGCombiner::MergeConsecutiveStores, there is this check:

     if (Index->getAlignment() != St->getAlignment())
       break;

Apparently this check ensures that all of the stores have the same
alignment.  Why is that necessary?  This seems very overly restrictive
to me.

                            -David

Hi David, 

You are right. This check is overly restrictive. We can replace this check with
code that uses the alignment of the first store.

Thanks,
Nadav

On Nov 22, 2013, at 9:31 AM, dag at cray.com wrote:
> In DAGCombiner::MergeConsecutiveStores, there is this check:
> 
>     if (Index->getAlignment() != St->getAlignment())
>       break;
> 
> Apparently this check ensures that all of the stores have the same
> alignment.  Why is that necessary?  This seems very overly restrictive
> to me.
> 
>                            -David
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

On Nov 22, 2013, at 9:38 AM, Nadav Rotem <nrotem at apple.com> wrote:
> Hi David, 
> 
> You are right. This check is overly restrictive. We can replace this check
with code that uses the alignment of the first store.
Except for cases where the alignment is zero, which is the natural alignment of
the type.  :)

> 
> Thanks,
> Nadav
> 
> On Nov 22, 2013, at 9:31 AM, dag at cray.com wrote:
> 
>> In DAGCombiner::MergeConsecutiveStores, there is this check:
>> 
>>    if (Index->getAlignment() != St->getAlignment())
>>      break;
>> 
>> Apparently this check ensures that all of the stores have the same
>> alignment.  Why is that necessary?  This seems very overly restrictive
>> to me.
>> 
>>                           -David
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> 
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev